Heat shock augments myosin phosphatase target-subunit phosphorylation

Our previous study demonstrated that heat shock augmented vascular contraction. In the present study, we hypothesized that heat shock augments myosin phosphatase target-subunit (MYPT1) phosphorylation resulting in augmented vascular contraction. Endothelium-denuded rat aortic rings were mounted in organ baths, exposed to heat shock (42 °C for 45 min), and subjected to contraction 4 h after the heat shock followed by Western blot analysis for MLC₂₀ (the 20 kDa light chains of myosin II) or MYPT1. The contractile responses in both control and heat shock-treated aorta were inhibited by Y27632, an inhibitor of Rho-kinase. The level of the MLC₂₀ and MYPT1^Thr855 phosphorylation in response to KCl was higher in heat shock-treated aorta than that in timed-control. The increased MYPT1^Thr855 phosphorylation was inhibited by Y27632 (1.0 μM) in parallel with inhibition of MLC₂₀ phosphorylation and vascular contraction. These results indicate that heat shock augments MYPT1 phosphorylation resulting in augmented vascular contraction.