Inhibition of protein kinase C-mediated contraction by Rho kinase inhibitor fasudil in rabbit aorta
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The original publication is available at www.springerlink.comProtein kinase C (PKC) activation by a phorbol ester increases myosin light chain (MLC20) phosphorylation through inhibition of MLC phosphatase (MLCP) and enhances contraction of vascular smooth muscle.We investigated whether Rho kinase, which is known to inhibit MLCP, is involved in the MLC20 phosphorylation caused by a phorbol ester, 12-deoxyphorbol 13-isobutyrate (DPB), in rabbit aortas. DPB (1 μM) increased MLC20 phosphorylation and tension. The Rho kinase inhibitor fasudil (10 μM) inhibited the DPB-induced contraction and decreased the MLC20 phosphorylation at Ser19, a site phosphorylated by MLC kinase, although it did not affect the phosphorylation of total MLC20.Rinsing a 65.4 mM KCl-contracted aorta with Ca2+-free, EGTA solution caused rapid dephosphorylation of MLC20 and relaxation. When DPB was present in the rinsing solution, the MLC20 dephosphorylation and the relaxation were inhibited. In this protocol，Ro31-8220 (10 μM), a PKCinhibitor, suppressed the phosphorylation of total MLC20 and Ser19 inducedby DPB. Fasudil also inhibited the Ser19 phosphorylation to a degree similarto Ro31-8220 and accelerated relaxation, which was less than the relaxationcaused by Ro31-8220. The phospholipase A2 inhibitor ONO-RS-082 (5 μM) inhibited the DPB-induced Ser19 phosphorylation but only transiently decreased the tension, suggesting the involvement of arachidonic acid in the phosphorylation but also the existence of a MLC20 phosphorylation-independent mechanism. When fasudil was combined with ONO-RS-082, fasudil exerted additional inhibition of the tension withoutfurther inhibition of the Ser19 phosphorylation. DPB phosphorylated the 130kDa myosin binding subunit of MLCP and fasudil inhibited the phosphorylation.These data suggest that the inhibition by fasudil of DPB-induced contraction and phosphorylation of MLC20 at the MLC kinase-targeted site is a result of inhibition of Rho kinase. Thus, the PKC-dependentCa2+-sensitization of vascular smooth muscle involves Rho kinase. A MLC20 phosphorylation-independent mechanism is also involved in the Ca2+-sensitization.
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