Figure 1

Threshold for temperature dependent increase in ser¹⁶-HSP20 phosphorylation and force suppression. Swine carotid artery tissues were exposed to various temperatures between 2°C and 47.5°C (shown on abscissa) for 4 hours, then returned to 37°C for 1 hour, and stimulated with 10 μM histamine for 10 min before freezing. Histamine induced ser¹⁶-HSP20 phosphorylation (mol P_i at ser 16 / mol HSP20) is shown in the top panel, putative PKC-HSP20 phosphorylation (mol P_i at the PKC site / mol HSP20) in the second panel, ser¹⁹-MRLC phosphorylation (mol P_i at ser 19 / mol MRLC) in the third panel, and force in the bottom panel (n = 4–8, except n = 3 at 14 & 20°C and n = 2 at 8°C, data presented as mean ± 1 SEM). Ser¹⁹-MRLC phosphorylation measurements were limited to tissues treated at 37°C, 44.5°C, and 47.5°C. Force was significantly reduced in tissues treated at 44.5°C or higher compared to 41.5°C or lower. Ser¹⁶-HSP20 phosphorylation was significantly higher in tissues treated between 43 and 46°C compared to tissues treated at less than 43°C or at 47.5°C. PKC-HSP20 phosphorylation did not significantly change. At temperatures between 43 and 46°C, low force was associated with elevated ser¹⁶-HSP20 phosphorylation levels despite elevated ser¹⁹-MRLC phosphorylation levels. At 47.5°C, reduced force was associated with significantly reduced ser¹⁹-MRLC phosphorylation (compared to tissues treated at 37°C or 44.5°C, i.e. there was deactivation).