Sustained muscle contraction induced by agonists, growth factors, and Ca mediated by distinct PKC isozymes

Murthy, K. S., J. R. Grider, J. F. Kuemmerle, and G. M. Makhlouf. Sustained muscle contraction induced by agonists, growth factors, and Ca mediated by distinct PKC isozymes. Am J Physiol Gastrointest Liver Physiol 279: G201–G210, 2000.—The role of protein kinase C (PKC) in sustained contraction was examined in intestinal circular and longitudinal muscle cells. Initial contraction induced by agonists (CCK-8 and neuromedin C) was abolished by 1) inhibitors of Ca mobilization (neomycin and dimethyleicosadienoic acid), 2) calmidazolium, and 3) myosin light chain (MLC) kinase (MLCK) inhibitor KT-5926. In contrast, sustained contraction was not affected by these inhibitors but was abolished by 1) the PKC inhibitors chelerythrine and calphostin C, 2) PKC-e antibody, and 3) a pseudosubstrate PKC-e inhibitor. GDPbS abolished both initial and sustained contraction, whereas a Gaq/11 antibody inhibited only initial contraction, implying that sustained contraction was dependent on activation of a distinct G protein. Sustained contraction induced by epidermal growth factor was inhibited by calphostin C, PKC-a,b,g antibody, and a pseudosubstrate PKC-a inhibitor. Ca (0.4 mM) induced an initial contraction in permeabilized muscle cells that was blocked by calmodulin and MLCK inhibitors and a sustained contraction that was blocked by calphostin C and a PKC-a,b,g antibody. Thus initial contraction induced by Ca, agonists, and growth factors is mediated by MLCK, whereas sustained contraction is mediated by specific Ca-dependent and -independent PKC isozymes. G protein-coupled receptors are linked to PKC activation via distinct G proteins.