Heat induced HSP20 phosphorylation without increased cyclic nucleotide levels in swine carotid media

BACKGROUND: Heat pretreatment of swine carotid artery has been shown to increase ser(16)-heat shock protein 20 (HSP20) phosphorylation and suppress force, i.e., reduce force with only minimal reduction in ser(19)-myosin regulatory light chain (MRLC) phosphorylation. RESULTS: We further investigated this response in intact histamine stimulated swine carotid artery rings. There was a heat threshold such that increased ser(16)-HSP20 phosphorylation and force suppression were observed between 43°C and 46°C. The increased ser(16)-HSP20 phosphorylation persisted up to 16 hours after 44.5°C heat treatment. Pretreatment of swine carotid media at 44.5°C increased ser(16)-HSP20 phosphorylation without increases in [cAMP] or [cGMP], suggesting an alternate mechanism, perhaps phosphatase inhibition, for the increase in ser(16)-HSP20 phosphorylation. Heat pretreatment at 47.5°C reduced force by decreasing MRLC phosphorylation rather than by large increases in ser(16)-HSP20 phosphorylation. HSP20 phosphorylation at the putative PKC site did not change with any treatment. CONCLUSION: These results demonstrate that multiple mechanisms can induce force suppression that is correlated with ser(16)-HSP20 phosphorylation: 1) nitrovasodilators via cGMP, 2) forskolin via cAMP, and 2) thermal stress in a cyclic nucleotide independent manner.