Interactive role of protein phosphatase 2A and protein kinase cα in thestretch-induced triphosphorylation of myosin light chain in canine cerebral artery

Abstract

The interactive role of protein kinase C (PKC) isoforms and protein phosphatase 2A (PP2A) in the mechanisms underlying the gradual reduction in stretch-induced contraction through triphosphorylation of 20-kDa myosin light chain (MLC20) was investigated in the canine basilar artery. In the presence of 5 mM tetraethylammonium, stretching at a rate of 1 mm/s from the initial length (Li) to 1.5 Li produced a contraction. Maintaining the stretched state for 15 min (15-min stretch) produced triphosphorylation of MLC20at Ser-19, Thr-18 and Thr-9, and a gradual reduction in the contraction, both of which were reversed by Gö6976 (1 μM), an inhibitor of conventional PKC. The 15-min stretch increased PKCα activity whereas it decreased PP2A activity, both of which were blocked by Y-27632, an inhibitor of rho kinase. Okadaic acid (OA; 1 μM), a PP2A inhibitor, also produced triphosphorylation of MLC20 at the same amino acid residues and activated PKCα, which was inhibited by Gö6976. Stretching and OA increased phosphorylation of 17-kDa PKC-potentiated inhibitory phosphoprotein (CPI-17), and this phosphorylation was inhibited by Gö6976. The present results suggest that activation of PKCα mediated by an inhibitor of PP2A is involved in the stretch-induced triphosphorylation of MLC20, and that this triphosphorylation counteracts the stretch-induced contraction. Copyright © 2009 S. Karger AG, Basel.