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Figure 6 | BMC Physiology

Figure 6

From: Atypical properties of a conventional calcium channel β subunit from the platyhelminth Schistosoma mansoni

Figure 6

The N-terminal domain of SmCa v β is the molecular substrate for Na+ and Mg2+-ATP mediated block of Ca v 2.3 currents. A. Diagram showing the portion of the N-terminal domain, including a domain rich in aspartic acid and glutamic acid (DE-rich domain), that is removed by the truncation. Acidic residues are in red. B. Current-voltage relationships from HEK cells expressing Cav2.3 alone (filled circles) and in combination with SmCavβ (open circles) or N-terminally truncated SmCavβ (filled triangles). Peak currents generated by voltage steps from -20 mV to +75 mV in 5 mV steps from a holding potential of -80 mV were measured. Data points represent mean ± s.e.m. N = 6–7. C. Voltage-dependence of inactivation (steady-state inactivation) for Cav2.3 alone co-expressed with SmCavβ (filled circles) or with its N-terminally truncated version (open circles). Lines represent fits to the Boltzmann function. D. Relative peak current amplitude of currents produced by Cav2.3 channels in the presence of internal 5 mM Mg2+-ATP co-expressed with the wild type SmCavβ subunit (filled circles) or with the N-terminally truncated SmCavβ subunit (open circles) plotted as a function of time. Currents were normalized with respect to those measured immediately after rupturing the patch membrane (t = 0). Data points represent mean ± s.e.m. N = 5. E. Relative current amplitude of currents produced by Cav2.3 channels in the presence of internal 5 mM NaCl co-expressed with the wild type SmCavβ subunit (filled circles) or with the N-terminally truncated SmCavβ subunit (open circles) plotted as a function of time. Currents were normalized with respect to those measured immediately after rupturing the patch membrane (t = 0). Data points represent mean ± s.e.m. N = 10–13. F. Comparison between the relative current amplitudes produced by Cav2.3 channels co-expressed with SmCavβ (in black) or with its N-terminally truncated version (in grey), in the presence of intracellular 5 mM Mg2+-ATP (left), or in the presence of 5 mM NaCl (right), after 2.5 minutes of establishing the whole-cell configuration. Asterisks denote statistical difference with respect to current amplitude for Cav2.3 co-expressed with wild type SmCavβ (Student t test, p < 0.05).

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