INVOLVEMENT OF RHO IN GTP-GAMMA-S-INDUCED ENHANCEMENT OF PHOSPHORYLATION OF 20 KDA MYOSIN LIGHT-CHAIN IN VASCULAR SMOOTH-MUSCLE CELLS - INHIBITION OF PHOSPHATASE-ACTIVITY

In beta-escin-permeabilized cultured pig aortic smooth muscle cells GT P gamma S dose-dependently enhances Ca2+-induced, wortmannin-sensitive phosphorylation of 20 kDa myosin light chain (MLC(20)), GTP gamma S d oes not potentiate thiophosphorylation of MLC(20), but does inhibit it s dephosphorylation, Pretreatment with C, botulinum exotoxin C-3, whic h specifically ADP-ribosylates and inactivates the rho family of the s mall molecular weight G proteins, completely abolishes the effects of GTP gamma S, These results indicate that rite is involved in the GTP g amma S-induced enhancement of Ca2+-dependent MLC(20) phosphorylation i n aortic smooth muscle cells, and strongly suggest that this effect of rho is due to inhibition of protein phosphatase activity toward MLC(2 0).