Heat-shock response is associated with enhanced contractility of vascular smooth muscle in isolated rat aorta

Stress proteins have been implicated in pathological cardiovascular conditions. We hypothesized that a heat-shock response modulates contractility of vascular smooth muscles. Rat aortic ring preparations were mounted in organ baths, exposed to 42°C for 45 min, and subjected to contractions. Expression of HSP70 and phosphorylation of myosin light chain were examined with immunoblots. Heat shock enhanced contractile response to KCl in parallel with HSP70 expression in rat aortic rings from 8 h but not 1 h after the end of heat shock. Heat shock also augmented vascular contractility to phenylephrine whether endothelium was intact or denuded. Treatment of heat shock-preconditioned aortic rings with Bay K8644, a calcium channel activator, but not treatment with phorbol dibutyrate (1 μmol/l), a protein kinase C activator, enhanced contractions of the rings as compared with those of the control. The levels of phosphorylation of myosin light chains after administration of phenylephrine in heat shock-preconditioned tissues were statistically significantly higher than those in control tissues. Pretreatment with wortmannin (300nmol/l), an inhibitor of myosin light chain kinase, decreased both contractility and phosphorylation of myosin light chains in parallel. However, heat-shock response did not affect relaxation responses to either acetylcholine in endothelium-intact aortic rings or sodium nitroprusside in endothelium-denuded rings. These results suggest that the heat-shock response is associated with enhanced vascular smooth muscle contractility through a modulation of thick-filament regulation.