Enhanced contraction and myosin phosphorylation induced by Ca2+-independent MLCK in spontaneously hypertensive rats

Abstract

[한글]

[영문]The aim of this study was to clarify the role of a possible Ca2+-independent myosin light chain kinase (MLCK) activity in hypertension. The increase in contractile force and phosphorylation of 20kDa regulatory light chains of myosin II (MLC20) evoked by the type 1 and 2A phosphatase inhibitor, calyculin A in beta-escin permeabilized mesenteric arteries at pCa9.0 were compared between Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). There is no detectable phosphorylation of MLC20 in permeabilized arteries at pCa9.0, but the administration of 1uM calyculin A gradually increased force and mono- and diphosphorylation of MLC20. This contraction is inhibited by staurosporine, a broad-spectrum protein kinase inhibitor but not by wortmannin, Y-27632, or calphostin-C. The calyculin A-induced contraction is significantly greater in SHR than WKY and it was associated with an increase in mono- and diphosphorylation of MLC20. SM-1, a ZIPK inhibiting peptide, significantly inhibits the amplitude of the calyculin A-induced contraction. Total ZIPK expression (54 and 32 kDa) is greater in SHR than WKY. Phosphorylation of MYPT1 at Thr-697, but not at Thr-855, is consistently stronger in SHR compared with WKY in calyculin A-treated tissues at pCa9.0. These results suggest that a Ca2+-independent MLCK activity is enhanced in SHR and ZIPK is the key candidate for this kinase in rat mesenteric arteries. Furthermore, the higher expression level of ZIPK in SHR appears to increase Thr-697 phosphorylation of MYPT1, MLC20 phosphorylation and contraction while calyculin A induces phosphatase inhibition in SHR.