Abstract Objective: Hypoxia induces coronary artery dilation, but the responsible mechanism is largely unknown. Many stimuli induce arterial smooth muscle relaxation by reducing ser19-myosin regulatory light chain (MLC) phosphorylation. Other stimuli can induce smooth muscle relaxation without reductions in ser19-MLC phosphorylation. This form of relaxation has been termed force suppression and appears to be associated with heat shock protein 20 (HSP20) phosphorylation on ser16. We investigated whether hypoxia-induced sustained dilation in swine coronary arteries was promoted without ser19-MLC dephosphorylation and associated with ser16-HSP20 phosphorylation. Nitroglycerin vasodilation served as control. Methods: In a pressure myograph, the tunica media of intact pre-contracted (PGF2α; 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 m, 90 min), and nitroglycerin + wash-out (60 min). The arterial segments were snap-frozen and analysed for ser16-HSP20 phosphorylation and ser19-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). Ser16-HSP20 phosphorylation was increased with hypoxia and nitroglycerin treatment and ser16-HSP20 phosphorylation correlated with changes in diameters (n = 29, r2 = 0.64, P < 0.001). Ser19-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 ser16-HSP20 phosphorylation. Conclusion: Ser16-HSP20 phosphorylation is a potential regulator of hypoxia-induced dilation in coronary arteries.
Department of Pharmacology, University of Aarhus, Aarhus, Denmark 2:
Cardiovascular Division, Departments of Internal Medicine and Physiology, University of Virginia Health System, Charlottesville, VA, USA