HSP20 phosphorylation and interstitial metabolites in hypoxia-induced dilation of swine coronary arteries

Objective: Hypoxia induces coronary artery dilation, but the responsible mechanism is largely unknown. Many stimuli induce arterial smooth muscle relaxation by reducing ser(19)-myosin regulatory light chain (MLC) phosphorylation. Other stimuli can induce smooth muscle relaxation without reductions in ser(19)-MLC phosphorylation. This form of relaxation has been termed force suppression and appears to be associated with heat shock protein 20 (HSP20) phosphorylation on ser(16). We investigated whether hypoxia-induced sustained dilation in swine coronary arteries was promoted without ser(19)-MLC dephosphorylation and associated with ser(16)-HSP20 phosphorylation. Nitroglycerin vasodilation served as control. Methods: In a pressure myograph, the tunica media of intact pre-contracted (PGF(2 alpha); 10(-5) M) porcine coronary artery segments were cannulated using a microdialysis catheter. Diameter responses and interstitial lactate/pyruvate ratios were studied during 90 min hypoxia, hypoxia + reoxygenation ( 60 min), nitroglycerin ( 100 mu M, 90 min), and nitroglycerin + wash-out ( 60 min). The arterial segments were snap-frozen and analysed for ser(16)-HSP20 phosphorylation and ser(19)-MLC phosphorylation. Results: The normalized diameter responses to hypoxia (6.1 +/- 4.3%) and nitroglycerin (12.6 +/- 1.6%) were both significantly greater than normoxic control arteries (-10.5 +/- 1.8%, ANOVA, P < 0.05). Ser(16)-HSP20 phosphorylation was increased with hypoxia and nitroglycerin treatment and ser(16)-HSP20 phosphorylation correlated with changes in diameters ( n = 29, r(2) = 0.64, P < 0.001). Ser(19)-MLC phosphorylation was not significantly altered by hypoxia. The lactate/pyruvate ratio was significantly increased in hypoxic arteries but did not correlate with diameters or ser(16)-HSP20 phosphorylation. Conclusion: Ser(16)-HSP20 phosphorylation is a potential regulator of hypoxia-induced dilation in coronary arteries.