Involvement of rho in GTPγS‐induced enhancement of phosphorylation of 20 kDa myosin light chain in vascular smooth muscle cells: inhibition of phosphatase activity

摘要

>In β-escin-permeabilized cultured pig aortic smooth muscle cells GTPγS dose-dependently enhances Ca2+-induced wortmannin-sensitive phosphorylation of 20 kDa myosin light chain (MLC₂₀). GTPγS does not potentiate thiophosphorylation of MLC₂₀, but does inhibit its dephosphorylation. Pretreatment with C. botulinum exotoxin C₃, which specifically ADP-ribosylates and inactivates the rho family of the small molecular weight G proteins, completely abolishes the effects of GTPγS. These results indicate that rho is involved in the GTPγS-induced enhancement of Ca2+-dependent MLC₂₀ phosphorylation in aortic smooth muscle cells, and strongly suggest that this effect of rho is due to inhibition of protein phosphatase activity toward MLC₂₀.