Sinoatrial tissue of crucian carp heart has only negative contractile responses to autonomic agonists
© Vornanen et al; licensee BioMed Central Ltd. 2010
Received: 9 December 2009
Accepted: 11 June 2010
Published: 11 June 2010
In the anoxia-tolerant crucian carp (Carassius carassius) cardiac activity varies according to the seasons. To clarify the role of autonomic nervous control in modulation of cardiac activity, responses of atrial contraction and heart rate (HR) to carbacholine (CCh) and isoprenaline (Iso) were determined in fish acclimatized to winter (4°C, cold-acclimated, CA) and summer (18°C, warm-acclimated, WA) temperatures.
Inhibitory action of CCh was much stronger on atrial contractility than HR. CCh reduced force of atrial contraction at an order of magnitude lower concentrations (EC50 2.75-3.5·10-8 M) in comparison to its depressive effect on HR (EC50 1.23-2.02·10-7 M) (P < 0.05) without differences between winter and summer acclimatized fish. Inhibition of nitric oxide synthase with 100 μM L-NMMA did not change the response of the sinoatrial tissue to CCh. Reduction of atrial force was associated with a strong shortening of action potential (AP) duration to ~50% (48 ± 10 and 50 ± 6% for CA and WA fish, respectively) and 11% (11 ± 3 and 11 ± 2% for CA and WA fish, respectively) of the control value at 3·10-8 M and 10-7 M CCh, respectively (P < 0.05). In atrial myocytes, CCh induced an inwardly rectifying K+ current, IK,CCh, with an EC50 value of 3-4.5·10-7 M and inhibited Ca2+ current (ICa) by 28 ± 8% and 51 ± 6% at 10-7 M and 10-6 M, respectively. These currents can explain the shortening of AP. Iso did not elicit any responses in crucian carp sinoatrial preparations nor did it have any effect on atrial ICa, probably due to the saturation of the β-adrenergic cascade in the basal state.
In the crucian carp, HR and force of atrial contraction show cardio-depressive responses to the cholinergic agonist, but do not have any responses to the β-adrenergic agonist. The scope of inhibitory regulation by CCh is increased by the high basal tone of the adenylate cyclase-cAMP cascade. Higher concentrations of CCh were required to induce IK,CCh and inhibit ICa than was needed for CCh's negative inotropic effect on atrial muscle suggesting that neither IK,CCh nor ICa alone can mediate CCh's actions but they might synergistically reduce AP duration and atrial force production. Autonomic responses were similar in CA winter fish and WA summer fish indicating that cardiac sensitivity to external modulation by the autonomic nervous system is not involved in seasonal acclimatization of the crucian carp heart to cold and anoxic winter conditions.
Crucian carp (Carassius carassius L.) is one of the most anoxia tolerant vertebrates and the only fish species in North temperate latitudes tolerates prolonged and total oxygen shortage. Therefore crucian carp thrive as dense single-species populations in seasonally anoxic ponds and lakes [1–3]. The success of crucian carp in inhabiting oxygen deprived environments is based on unsurpassed physiological adaptations to anoxia which involve huge carbohydrate stores throughout the body, anoxic metabolic depression, production of ethanol as an anaerobic end product, molecular mechanisms to allow anoxic brain survival, modification of gill structure to reduce ion loss in anoxia and inverse thermal compensation of heart function to minimize cardiac energy consumption in the anoxic and cold winter waters [4–8]. These adaptations are probably crucial for survival under severe hypoxia/anoxia up to 6 months in the ice covered lakes .
The vertebrate heart serves body homeostasis by distributing oxygen, metabolite substrates and hormonal messages throughout the body. In severely hypoxic or anoxic conditions, demands for oxygen convection diminish or completely disappear in the body of crucian carp, and due to a low metabolic rate in the cold, circulatory requirements for integrative functions are expected to reduce. Indeed, the heart of crucian carp shows clear seasonality in having larger glycogen reserves and fewer sarcolemmal (SL) L-type Ca2+ channels and expressing lower myosin ATPase activity in winter than summer [3, 9]. Furthermore, winter acclimatized fish show depressed SL Na+ currents and increased K+ currents in the heart [10–12]. These findings indicate that several intrinsic mechanisms of crucian carp cardiac myocytes are acclimatized to changing circulatory demands in seasonally varying habitat conditions and suggest that cardiac contractility is reduced in winter anoxia. However, the significance of extrinsic modulators of the heart, in particular the autonomic nervous regulation, is less well understood in the physiology of crucian carp and other anoxia-tolerant vertebrates.
In various physiological situations, contractility of the vertebrate heart is adjusted to circulatory demands by intrinsic length-dependent changes in individual myocytes [13, 14] and by extrinsic modulators, mainly by the autonomic nervous system . Vertebrate hearts usually have dual autonomic innervation through inhibitory cholinergic nerves and stimulatory adrenergic nerves, which modulate heart rate (HR), impulse conduction and force of contraction via specific membrane receptors and intracellular signaling cascades [16, 17].
Noradrenaline and adrenaline of the sympathetic nervous system increase heart rate and force of contraction mainly by binding to beta-adrenergic receptors which use the cAMP-dependent pathway to increase SL Ca2+ current (ICa) and sarcoplasmic reticulum (SR) Ca2+ uptake and release [17–19].
Acetylcholine (ACh) of the parasympathetic nervous system exerts a direct negative chronotropic effect on the sinoatrial nodal tissue, a negative dromotropic effect on atrio-ventricular conduction and a direct negative inotropic effect on the atria. Furthermore ACh has an indirect negative inotropic effect which is observed both in atrial and ventricular muscle in the presence of sympathetic tone. In isolated cardiac myocytes, muscarinic cholinergic agonists reduce and/or eliminate beta-adrenergic stimulation of the Ca2+ current (ICa), possibly by G-protein dependent inhibition of the adenylate cyclase. In the absence of beta-adrenergic stimulation, i.e. under basal conditions, ACh depresses ICa if the adenylate cyclase is under a tonic activation [20, 21].
Considering the drastic seasonal changes in abiotic conditions (temperature, oxygen content) of crucian carp habitat and associated alterations in functional demands on cardiac function, it could be anticipated that the extrinsic control mechanisms of the crucian crap heart might change according to the seasons. Therefore, the aim of the present study is to elucidate responses of the crucian carp sinoatrial preparations to sympathetic and parasympathetic agonists in fish acclimatized to winter and summer conditions. Specifically, it was hypothesized that negative parasympathetic responses are enhanced in winter and excitatory adrenergic effects are up-regulated in summer.
Responses of the sinoatrial tissue to carbacholine (CCh)
Heart rate and variables of atrial contraction in sinoatrial preparations of thermally acclimated crucian carp
4°C acclimated fish
18°C acclimated fish
Heart rate (beats/min)
11.2 ± 0.5*
52.1 ± 1.7
1.2 ± 0.4*
3.4 ± 0.6
Time to peak force (ms)
774.3 ± 47.5*
237.4 ± 4.5
Time to half of relaxation (ms)
914.0 ± 45.2*
278.5 ± 8.2
Maximal rate of rise (mN/mg/ms)
0.04 ± 0.2*
0.21 ± 0.3
Maximal rate of fall (mN/mg/ms)
0.03 ± 0.1*
0.14 ± 0.2
Size of atrial tissues (mg)
6.71 ± 0.4
6.90 ± 0.6
EC50-values (concentration for half-maximal effect) of CCh for contractile and electrophysiological parameters of the crucian carp sinoatrial tissue and atrial cardiomyocytes
4°C acclimated fish EC50
18°C acclimated fish EC50
Statistically significant differences (p < 0.05) between mean EC50 values with the listed parameters
2.02e-7 ± 0.2
1.23e-7 ± 0.03
3.50e-8 ± 0.03
2.75e-8 ± 0.1
HR, DC, IK
1.11e-7 ± 0.1
1.46e-7 ± 0.1
IK, CCh at 4°C/18°C
4.47e-6 ± 0.2
3.47e-6 ± 0.7
HR, Fmax, DC
Taken together, these findings demonstrate a strong inhibitory effect of muscarinic cholinergic receptors on crucian carp heart and a large difference in sensitivity between chronotropic and inotropic responses to CCh.
Effect of nitric oxidase synthase (NOS) inhibitor on CCh response
100 μM L-NMMA did not modify CCh's influence on HR and atrial contraction thus suggesting that NO generation by endocardial endothelial cells (or myocytes) is not involved CCh's negative chronotropic and inotropic effects in crucian carp sinoatrial tissue (Figure 1, inset).
Responses of sinoatrial preparations to isoprenaline (Iso)
Collectively, these findings indicate negligible inotropic and chronotropic effects of beta-adrenergic stimulation in the crucian carp heart possibly due to the saturation of the signal transduction cascade under basal conditions (see Effects of CCh on L-type Ca 2+ current of atrial myocytes).
Effects of CCh on action potential (AP) and K+ currents of atrial myocytes
Effect of CCh on L-type Ca2+ current in atrial myocytes
The autonomic nervous system represents a major regulatory mechanism for short-term and long-term adjustments of cardiac function via muscarinic cholinergic and beta-adrenergic receptors [16, 17]. Seasonal changes in autonomic nervous regulation and neurotransmitter content of the heart has been demonstrated in ectothermic vertebrates [22, 23]. Therefore, we hypothesized that autonomic regulation is involved in seasonal acclimatization of the crucian carp heart so that negative cholinergic responses would prevail in winter to down-regulate cardiac function in the cold and anoxic winter waters, while stimulatory adrenergic responses could be stronger in summer to allow enhancement of cardiac activity in warm and oxygen rich waters. The main result in this regard is that little differences in autonomic responses exist between summer and winter fish hearts and therefore the above hypothesis must be abandoned. Obviously, seasonal acclimatization of the crucian carp heart is mainly dependent on intrinsic molecular adjustments within individual cardiac myocytes [3, 9, 24, 25], while sensitivity to extrinsic modulation of cardiac function by the autonomic nervous system remain unaltered throughout the year. Nevertheless, the sinoatrial tissue of crucian carp heart is under a strong inhibitory cholinergic control in summer and in winter.
The present experiments indicate two major findings on autonomic nervous regulation of the crucian carp heart. First, the crucian carp sinoatrial tissue lacks the ability for up-regulation of cardiac activity above the basal level, i.e. there are no stimulatory responses to the beta-adrenergic agonist Iso. Second, atrial force generation is much more sensitive to muscarinic cholinergic inhibition than is firing rate of the sinoatrial pacemaker. CCh concentrations (3·10-8 M - 7·10-8 M) that significantly inhibit atrial force have practically no effect on HR. These characteristics raise questions about the physiological significance of autonomic regulation in the function of crucian carp heart and their molecular mechanisms.
Cholinergic regulation of the crucian carp heart
Major mechanisms for down-regulation of atrial contractility by the cholinergic system are induction of the IK,CCh and inhibition of the ICa . Both mechanisms curtail the duration of AP which therefore indirectly reduce SL Ca2+ influx via Ca2+ channels and the reverse mode of Na+-Ca2+ exchange (NCX). Furthermore CCh reduces phosphorylation of the L-type Ca2+ channels and thereby the density of the ICa independently from changes in AP duration [20, 21] (see Figure 8). The present experiments on isolated atrial cardiomyocyte show that IK,CCh is induced and ICa inhibited by CCh. Hence both mechanisms could potentially contribute to CCh-dependent shortening of AP and consequently to the negative inotropic effect of CCh in the crucian carp heart. However, activation of the currents in isolated myocytes required higher concentrations of CCh than were necessary to induce negative inotropic effects in intact sinoatrial preparations. Therefore changes in IK,CCh and ICa do not entirely explain the observed contractile response. This discrepancy might be due to different preparations used for force (intact tissue) and current (isolated myocytes) measurements, in particular due to the presence of endocardial endothelium in the intact tissue which is known to modify cholinergic responses via activation of the endothelial NOS (see Figure 8). However, L-NMMA, an inhibitor of NOS, did not affect CCh responses of the intact sinoatrial tissue, strongly suggesting that NOS activity is not required for the full sensitivity of the atrial tissue to cholinergic agonists in the crucian carp heart. Nitric oxide generation seems to be an obligatory process in cholinergic inhibition of ICa in mammalian pacemaker tissue  and endocardial endothelium is found to be necessary for the negative inotropic effect of ACh in the frog (R. pipiens) heart . On the other hand, ACh inhibits ICa independent from protein phosphatases or NOS in human atrial tissue . Collectively these findings indicate that contribution of the endocardial NOS to cholinergic responses of the vertebrate heart is species and tissue dependent, and suggest that crucian carp belong to the group which is independent of NOS signaling. However, the presence and activity of NOS and neuropeptides which may modulate autonomic nervous transmission in fish  need to be examined with more direct methods in the heart of crucian carp.
The plateau of the cardiac AP is maintained by a balance between small outward K+ currents and a small inward Ca2+ current, and due to the high membrane resistance, fairly small changes in ion conductance can alter AP duration. Hence, only small variations in IK,CCh and ICa, which synergistically contribute to the shortening of AP duration during cholinergic activation, are needed to produce a strong shortening of AP duration. A maximally effective concentration of CCh (10-7 M) produces ~30% inhibition of atrial ICa which depresses atrial force with 34-41%. This indirect experimental analysis indicates that CCh-dependent inhibition of ICa alone is capable for almost one third of the CCh's negative inotropic action. Although the same concentration of CCh (10-7 M) activates only a small portion (about 2% of the maximum) of the IK,CCh,, the outward IK,CCh at 0 mV is 2-3 times larger than the background inward rectifier (IK1) and therefore strongly repolarizing. This is because of the weak inward rectification of the IK,CCh which makes this current a very effective regulator of AP duration. Thus, full activation of the IK,CCh and complete inhibition of the ICa are not needed to produce strong AP shortening and a negative inotropic response. Due to the synergistic action of IK,CCh and ICa, it is impossible to provide exact quantitative estimates on the relative importance of IK,CCh and ICa in the negative inotropic effect of CCh, even though IK,CCh seems to be more important.
An interesting finding is that depression of atrial contraction force occurs prior to the bradycardic response. Almost 80% of the atrial force can be inhibited before CCh's effect on HR starts to appear, i.e. under weak and moderate cholinergic tone atrial contraction is strongly depressed without changes in HR. Similar dichotomy between inotropic and chronotropic effects of cholinergic activation has been noted in the tilapia (Orechormis nilotica/aureus) heart . The dissociation of inotropic and chronotropic responses to muscarinic activation probably provides a finely tuned mechanism to regulate cardiac output first by reducing end-diastolic filling of the ventricle via weakened atrial contraction and then via depression of contraction frequency.
The absence of beta-adrenergic stimulation
The sinoatrial tissue of the crucian carp heart is totally insensitive to beta-adrenergic stimulation lacking both inotropic and chronotropic effects. The absence of these effects is unlikely to result from the research methods or experimental conditions as far as we can routinely measure chronotropic and/or inotropic responses in rainbow trout heart and ventricular muscle of the crucian carp under the same conditions [37, 38]. Although cholinergic effects are commonly much stronger than adrenergic effects in teleost hearts, total insensitivity of the fish heart to beta-agonists is, however, rare [15, 26]. Ventricular muscle of the crucian carp heart is also fairly insensitive to beta-adrenergic activation, as adrenaline and Iso cause about a modest 10% and 40% increase in the force of contraction, respectively . The absence of beta-adrenergic response in sinoatrial tissue of the crucian carp heart is probably due to maximal or near maximal activation of the molecular machinery involved in beta-adrenergic signaling pathway, in particular the L-type Ca2+ channels, under basal conditions. Phosphorylation of L-type Ca2+ channels due to tonic activation of adenylate cyclase is not uncommon for the vertebrate atrial tissue and may hold true also for the crucian carp atrium. Thus, the present findings suggest that CCh-mediated antagonism of the cAMP-dependent signaling pathway results in dephosphorylation of L-type Ca2+ channels and thereby contribute to the decreased force production (see Figure 8).
Contractility of the crucian carp atrium seems to be tuned high by tonic activation of the adenylate cyclase-cAMP pathway, arguably to increase the scope of cholinergic regulation through the accentuated antagonism of adrenergic and cholinergic mechanisms . In their natural habitat crucian carp are exposed to prolonged winter anoxia. Anoxia has been shown to cause depletion of catecholamine stores of the head kidney in crucian carp , possibly due to oxygen requirement of catecholamine synthesis and short half-life of the catecholamine stores . In fish, oxygen deficiency is usually associated with a surge of catecholamines from the chromaffin tissue into the blood for modulation of cardiorespiratory functions and mobilization of the hepatic glycogen reserves . Cardiac stimulation by adrenergic cascade may be useful in hypoxia to optimize oxygen extraction from water, but probably inappropriate in the complete absence of oxygen. In anoxia it would increase cardiac energy consumption in situation where oxygen is not available and when the needs for oxygen convection in the body are abolished. Hence, the unresponsiveness of the crucian carp sinoatrial tissue to adrenergic agonists might serve to prevent unnecessary cardiostimulation upon exposure to complete and prolonged oxygen deficiency.
Autonomic regulation of HR
Depression of HR required higher CCh concentrations than inhibition of atrial force, suggesting a different mechanism of action. Pacemaker mechanism of the vertebrate heart is an outcome of intricate interactions between several sarcolemmal ion channels, Na+-Ca2+ exchange and sarcoplasmic reticulum Ca2+ release [42, 43]. Autonomic regulation of the pacemaker rate partly involves the same ionic mechanisms that are needed for regulation of atrial AP, but also additional ion channels like the pacemaker current, Ih . Muscarinic agonists can cause bradycardia by multiple mechanisms among others through the inhibition of Ih and ICa or activation of the IK,CCh [42, 43, 45]. The lower sensitivity of the crucian carp pacemaker to CCh in comparison to atrial myocytes may be related to the presence of additional ionic mechanisms of HR regulation, which are absent in atrial myocytes. Alternatively, there may be a lower number of cholinergic receptors in the atrial tissue. These issues cannot be resolved by the current results. Absence of the accelerating effect of Iso on HR suggests that a high constitutive activity of the adenylate-cyclase-cAMP signaling is also present in the pacemaker tissue. However, Stecyk et al.  noticed a moderate inhibition of heart rate by a beta-blocker propranolol when applied in vivo crucian carp. Whether this discrepancy between the two studies is due to different research methods (tissues and cells versus intact organism) or a genuine difference between larger lake form and smaller-sized pond form of the crucian carp is not known .
Sinoatrial tissue of the crucian carp heart lacks positive chronotropic and inotropic responses to autonomic nervous agonists and contractility can be only down-regulated through activation of the muscarinic cholinergic receptors. In resting conditions, the heart of crucian carp is under vagal tone [46, 47], and hence contractility of the sinoatrial tissue can be improved by relief of cholinergic control, even though the stimulatory adrenergic responses are completely absent. The stimulatory signaling pathway of the beta-adrenergic system may exist, but it does not elicit any significant responses in sinoatrial preparations due to the high basal activity of the adenylate cyclase-cAMP signaling. Basal activation of the cAMP pathway provides large scope for up- and down-regulation of contractility by cholinergic mechanisms even in the absence of beta-adrenergic stimulation. The insensitivity of the crucian carp heart to catecholamines prevents unnecessary activation of the heart under oxygen shortage, if hypoxia/anoxia causes a surge of catecholamines into the blood for activation of stress responses, e.g. glycogenolysis in the liver . The high sensitivity of atrial force to CCh suggests that cholinergic activation can cause reduced cardiac output (via reduced ventricular filling) without invoking bradycardia.
Collectively the present findings indicate that responsiveness of the crucian carp heart to extrinsic autonomic modulation is similar in summer and winter acclimatized fish. This is in sharp contrast to the many intrinsic properties of the crucian carp cardiac myocyte which are seasonally primed by environmental cues, in particular by temperature , to adjust cardiac function to seasonal changes in oxygen availability and temperature. It remains to be shown, however, whether the cholinergic tone itself is altered by seasons.
Crucian carp (49.2 ± 12.6 g, n = 83) were caught in June and November from a small local lake. In the laboratory, the fish caught in June and November were maintained at 18°C (warm-acclimated, WA) and 4°C (cold-acclimated, CA), respectively, which are close to the habitat temperatures of those seasons. Therefore throughout the text the terms winter-acclimatized and summer-acclimatized are used synonymous to CA and WA, respectively. Prior to the experiments, the fish were maintained at least four weeks at constant temperature and under a 15 h: 9 h light:dark photoperiod. During that time WA crucian carp were fed three times a week aquarium fish food (Tetra), while no food was provided to CA crucian carp as the winter acclimatized fish fast and deny from food. All experiments were conducted with the consent of the national committee for animal experimentation (permission STH252A).
Experiments on sinoatrial preparations
where Vmin is the value of the variable at the highest CCh concentration, Vmax the value of the variable before CCh addition, Kd the CCh concentration which causes half-maximal effect, [CCh] the CCh concentration, and H the Hill slope of the line. Atropine (3·10-6 M) and timolol (3·10-6 M) were used as the blockers of muscarinic cholinergic and beta-adrenergic receptors, respectively. Contractility of crucian carp sinoatrial preparation is stable for at least 3 hours and no corrections for time-dependent deterioration of force and heart rate were made.
Recording of atrial action potentials
For AP measurements sinoatrial preparations were gently fixed with insect pins on Sylgard-coated bottom of the 10-ml recording chamber filled with oxygenated (100% O2) physiological saline. The preparation was allowed to equilibrate for about 1 h to reach a stable beating rate before APs were recorded with sharp microelectrodes. Pipettes were fabricated from borosilicate glass with an internal filament using a Sutter P-97 puller and had a resistance of about 22 MΩs when filled with 3 M KCl. Analog signals were amplified by a high-impedance amplifier (KS-700, WPI, UK) and digitized (Digidata-1200 AD/DA board, Axon Instruments) with sampling rate of 2 kHz before storing on the computer with the aid of Axotape acquisition software . Because of difficulties in getting stable impalements of the cells with microelectrode on moving preparation, AP durations were measured only at three CCh concentrations. Recordings were taken when resting membrane potential was more negative than -60 mV. AP characteristics were analyzed with Clampfit software.
Measurement of sarcolemmal ion currents using the whole cell patch-clamp method
The whole-cell voltage clamp recording of Ca2+ and K+ currents was performed using an Axopatch 1-D (Axon) and an EPC-9 (HEKA Instruments, Germany) amplifier. A small aliquot of myocyte suspension was transferred to a recording chamber (RC-26; Warner Instrument Corp, Brunswick, CT, USA; volume 150 μl) and superfused with normal K+-based saline (containing in mmol l-1): 150 NaCl, 5.4 KCl, 1.8 CaCl2, 1.2 MgCl2, 10 glucose, 10 HEPES, with pH adjusted to 7.6 with NaOH). Temperature of the saline was adjusted to the desired value (4°C or 18°C) with Peltier devices (TC-10 or TC-100, Dagan Corporation, USA) and was continuously monitored with thermocouples positioned closed to the myocytes. Internal perfusion of the myocytes with K+-based electrode solution (containing in mmol l-1): 140 KCl, 1 MgCl2, 5 EGTA, 4 MgATP, and 10 HEPES with pH adjusted to 7.2 with KOH) giving a mean (± SE) pipette resistance of 3.17 ± 0.12 MΩ (n = 62). After gaining access to the cell, pipette capacitance (8.25 ± 0.22 pF) and series resistance (8.49 ± 0.48 MΩ) were compensated. When recording of CCh activated inward rectifier K+ currents (IK,CCh), tetrodotoxin (0.5 μM, Tocris Cookson, UK), nifedipine (10 μM, Sigma), E-4031 (1 μM, Alomone labs, Jerusalem, Israel) and glibenclamide (10 μM, Sigma) were always included in the external saline solution to prevent Na+, Ca2+ and ATP-sensitive K+ currents, respectively. When recording Ca2+ currents (ICa), KCl was replaced with equimolar CsCl in the bath and pipette solutions. TTX and E-4031 were added to the external saline to prevent Na+ current and Cs+ flux through the delayed rectifier K+ channels, respectively. When measuring ICa, CCh was applied with a fast solution changer (RSC-200, Biologic, Claix, France). Concentration-response curves were fitted with the Hill equation (see Experiments on sinoatrial preparations).
This study was supported by a grant (#127192) from the Academy of Finland to MV. We thank Anita Kervinen for skilful technical assistance.
- Holopainen IJ, Tonn WM, Paszkowski CA: Tales of two fish: the dichotomous biology of crucian carp (Carassius carassius (L.)) in northern Europe. Ann Zool Fenn. 1997, 28: 1-22.Google Scholar
- Piironen J, Holopainen IJ: A note on seasonality in anoxia tolerance of crucian carp (Carassius carassius L.) in the laboratory. Ann Zool Fenn. 1986, 23: 335-338.Google Scholar
- Vornanen M, Paajanen V: Seasonality of dihydropyridine receptor binding in the heart of an anoxia-tolerant vertebrate, the crucian carp (Carassius carassius L.). Am J Physiol. 2004, 287: R1263-R1269.Google Scholar
- Johnston IA, Bernard LM: Utilization of the ethanol pathway in carp following exposure to anoxia. J Exp Biol. 1983, 104: 73-78.Google Scholar
- Holopainen IJ, Hyvärinen H: Ecology and physiology of crucian carp (Carassius carassius (L.)) in small Finnish ponds with anoxic conditions in winter. Verh Internat Verein Limnol. 1985, 22: 2566-2570.Google Scholar
- Vornanen M, Paajanen V: Seasonal changes in glycogen content and Na+-K+-ATPase activity in the brain of crucian carp. Am J Physiol. 2006, 291: R1482-R1489.Google Scholar
- Nilsson GE: Surviving anoxia with the brain turned on. News in Physiological Sciences. 2001, 16: 217-221.PubMedGoogle Scholar
- Sollid J, Weber RE, Nilsson GE: Temperature alters the respiratory surface area of crucian carp Carassius carassius and goldfish Carassius auratus. J Exp Biol. 2005, 208: 1109-1116. 10.1242/jeb.01505.View ArticlePubMedGoogle Scholar
- Vornanen M: Seasonal adaptation of crucian carp (Carassius carassius L.) heart: glycogen stores and lactate dehydrogenase activity. Can J Zool. 1994, 72: 433-442. 10.1139/z94-061.View ArticleGoogle Scholar
- Haverinen J, Vornanen M: Temperature acclimation modifies Na+ current in fish cardiac myocytes. J Exp Biol. 2004, 207: 2823-2833. 10.1242/jeb.01103.View ArticlePubMedGoogle Scholar
- Haverinen J, Vornanen M: Responses of action potential and K+ currents to chronic thermal stress in fish hearts. Phylogeny or thermal preferences?. Physiol Biochem Zool. 2009, 82: 468-482. 10.1086/590223.View ArticlePubMedGoogle Scholar
- Hassinen M, Paajanen V, Vornanen M: A novel inwardly rectifying K+ channel, Kir2.5, is upregulated under chronic cold stress in fish cardiac myocytes. J Exp Biol. 2008, 211: 2162-2171. 10.1242/jeb.016121.View ArticlePubMedGoogle Scholar
- Allen DG, Kentish JC: The cellular basis of the length-tension relation in cardiac muscle. J Mol Cell Cardiol. 1985, 17: 821-840. 10.1016/S0022-2828(85)80097-3.View ArticlePubMedGoogle Scholar
- Shiels HA, Calaghan SC, White E: The cellular basis for enhanced volume-modulated cardiac output in fish hearts. J Gen Physiol. 2006, 128: 37-44. 10.1085/jgp.200609543.PubMed CentralView ArticlePubMedGoogle Scholar
- von Skramlik E: Über den Kreislauf bei den Fischen. Ergebnisse der Biologie. 1935, 11: 1-130.View ArticleGoogle Scholar
- Laurent P, Holmgren S, Nilsson S: Nervous and humoral control of the fish heart: structure and function. Comp Biochem Physiol. 1983, 76A: 525-542. 10.1016/0300-9629(83)90455-3.View ArticleGoogle Scholar
- Levy MN: Sympathetic-parasympathetic interactions in the heart. Circ Res. 1971, 29: 437-445.View ArticlePubMedGoogle Scholar
- Vornanen M: L-type Ca current in fish cardiac myocytes: effects of thermal acclimation and β-adrenergic stimulation. J Exp Biol. 1998, 201: 533-547.PubMedGoogle Scholar
- Llach A, Huang J, Sederat F, Tort L, Tibbits G, Hove-Madsen L: Effect of beta-adrenergic stimulation on the relationship between membrane potential, intracellular [Ca2+] and sarcoplasmic reticulum Ca2+ uptake in rainbow trout atrial myocytes. J Exp Biol. 2004, 207: 1369-1377. 10.1242/jeb.00884.View ArticlePubMedGoogle Scholar
- Harvey RD, Belevych AE: Muscarinic regulation of cardiac ion channels. Br J Pharmacol. 2001, 139: 1074-1084. 10.1038/sj.bjp.0705338.View ArticleGoogle Scholar
- Mery PF, Abi-Gerges N, Vandecasteele G, Jurevicius JA, Eschenhagen T, Fischmeister R: Muscarinic regulation of the L-type calcium current in isolated cardiac myocytes. Life Sci. 1997, 60: 1113-1120. 10.1016/S0024-3205(97)00055-6.View ArticlePubMedGoogle Scholar
- Temma K, Iwata M, Kondo H, Ohta T: Seasonal variations in the content of catecholamines in carp heart (Cyprinus carpio). Comp Biochem Physiol. 1990, 97C: 107-110.Google Scholar
- Harri MNE, Talo A: Effect of season and temperature acclimation on the heart rate-temperature relationship in the isolated frog's heart (Rana temporaria). Comp Biochem Physiol. 1975, 52A: 409-412. 10.1016/S0300-9629(75)80110-1.View ArticleGoogle Scholar
- Vornanen M: Seasonal and temperature-induced changes in myosin heavy chain composition of the crucian carp hearts. Am J Physiol. 1994, 267: R1567-R1573.PubMedGoogle Scholar
- Matikainen N, Vornanen M: Effect of season and temperature acclimation on the function of crucian carp (Carassius carassius) heart. J Exp Biol. 1992, 167: 203-220.Google Scholar
- Santer RM: Morphology and innervation of the fish heart. Adv Anat Embryol Cell Biol. 1985, 89: 1-102.View ArticlePubMedGoogle Scholar
- Cameron JS: Autonomic nervous tone and regulation of heart rate in the goldfish, Carassius auratus. Comp Biochem Physiol. 1979, 63C: 341-349.Google Scholar
- Fischmeister R, Castro L, Abi-Gerges A, Rochais F, Vandecasteele G: Species- and tissue-dependent effects of NO and cyclic GMP on cardiac ion channels. Comp Biochem Physiol. 2005, 142: 136-143. 10.1016/j.cbpb.2005.04.012.View ArticleGoogle Scholar
- Sartori C, Lepori M, Scherrer U: Interaction between nitric oxide and the cholinergic and sympathetic nervous system in cardiovascular control in humans. Pharmacol Ther. 2005, 106 (2): 209-220. 10.1016/j.pharmthera.2004.11.009.View ArticlePubMedGoogle Scholar
- Herring N, Danson EJF, Paterson DJ: Cholinergic control of heart rate by nitric oxide is site specific. News in Physiological Sciences. 2002, 17: 202-206.PubMedGoogle Scholar
- Hibino H, Inanobe A, Furutani K, Murakami S, Findlay I, Kurachi Y: Inwardly Rectifying Potassium Channels: Their Structure, Function, and Physiological Roles. Physiol Rev. 2010, 90: 291-366. 10.1152/physrev.00021.2009.View ArticlePubMedGoogle Scholar
- Han X, Shimoni Y, Giles WR: An obligatory role for nitric oxide in autonomic control of mammalian heart rate. J Physiol. 1994, 476 (2): 309-314.PubMed CentralView ArticlePubMedGoogle Scholar
- Amelio D, Garofalo F, Pellegrino D, Giordano F, Tota B, Cerra MC: Cardiac expression and distribution of nitric oxide synthases in the ventricle of the cold-adapted Antarctic teleosts, the hemoglobinless Chionodraco hamatus and the red-blooded Trematomus bernacchii. Nitric Oxide. 2006, 15: 190-198. 10.1016/j.niox.2005.12.007.View ArticlePubMedGoogle Scholar
- Jurevicius JA, Fischmeister R: Acetylcholine inhibits Ca2+ current by acting exclusively at a site proximal to adenylyl cyclase in frog cardiac myocytes. J Physiol. 1996, 491 (3): 669-675.PubMed CentralView ArticlePubMedGoogle Scholar
- Zaccone G, Mauceri A, Maisano M, Giannetto A, Parrino V, Fasulo S: Postganglionic nerve cell bodies and neurotransmitter localization in the teleost heart. Acta Histochem. 2009, 112: 328-336. 10.1016/j.acthis.2009.02.004.View ArticlePubMedGoogle Scholar
- Lin TC, Hsieh JC, Lin CI: Electromechanical effects of acetylcholine on the atrial tissues of the cultured tilapia (Oreochromis nilotica × O-aureus). Fish PhysiolBiochem. 1995, 14: 449-457. 10.1007/BF00004345.Google Scholar
- Vornanen M: Regulation of contractility of the fish (Carassius carassius L.) heart ventricle. Comp Biochem Physiol. 1989, 94C: 477-483.Google Scholar
- Aho E, Vornanen M: Cold-acclimation increases basal heart rate but decreases its thermal tolerance in rainbow trout (Oncorhynchus mykiss). J Comp Physiol B. 2001, 171: 173-179. 10.1007/s003600000171.View ArticlePubMedGoogle Scholar
- Nilsson GE: Long-term anoxia in crucian carp: changes in the levels of amino acid and monoamine neurotransmitters in the brain, catecholamines in chromaffin tissue, and liver glycogen. J Exp Biol. 1990, 150: 295-320.PubMedGoogle Scholar
- Iversen LL, Golowinski J: Regional differences in the rate of turnover of norepinephrine in the rat brain. Nature. 1966, 210: 1006-1008. 10.1038/2101006a0.View ArticlePubMedGoogle Scholar
- Keiver KM, Hochachka PW: Catecholamine stimulation of hepatic glycogenolysis during anoxia in the turtle Chrysemys picta. Am J Physiol. 1991, 261: R1341-R1345.PubMedGoogle Scholar
- Irisawa H: Comparative physiology of the cardiac pacemaker mechanism. Physiol Rev. 1978, 58: 461-498.PubMedGoogle Scholar
- Maltsev VA, Lakatta EG: Normal heart rhythm is initiated and regulated by an intracellular calcium clock within pacemaker cells. Am J Physiol. 2007, 16: 335-348.Google Scholar
- Warren KS, Baker K, Fishman MC: The slow mo mutation reduces pacemaker current and heart rate in adult zebrafish. Am J Physiol. 2001, 281: H1711-H1719.Google Scholar
- DiFrancesco D: Funny channels in the control of cardiac rhythm and mode of action of selective blockers. Pharmacol Res. 2006, 53: 399-406. 10.1016/j.phrs.2006.03.006.View ArticlePubMedGoogle Scholar
- Stecyk JAW, Stenslokken KO, Farrell AP, Nilsson GE: Maintained Cardiac Pumping in Anoxic Crucian Carp. Science. 2004, 306 (5693): 77-10.1126/science.1100763.View ArticlePubMedGoogle Scholar
- Vornanen M, Tuomennoro J: Effects of acute anoxia on heart function in crucian carp (Carassius carassius L.) heart: importance of cholinergic and purinergic control. Am J Physiol. 1999, 277: R465-R475.PubMedGoogle Scholar
- Tiitu V, Vornanen M: Cold adaptation suppresses the contractility of both atrial and ventricular muscle of the crucian carp (Carassius carassius L.) heart. J Fish Biol. 2001, 59: 141-156. 10.1111/j.1095-8649.2001.tb02344.x.View ArticleGoogle Scholar
- Haverinen J, Vornanen M: Temperature acclimation modifies sinoatrial pacemaker mechanism of the rainbow trout heart. Am J Physiol. 2007, 292: R1023-R1032.Google Scholar
- Vornanen M: Sarcolemmal Ca influx through L-type Ca channels in ventricular myocytes of a teleost fish. Am J Physiol. 1997, 272: R1432-R1440.PubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.