REGULATION OF PROTEIN-KINASES IN STEADY-STATE CONTRACTION OF CAT GASTRIC SMOOTH-MUSCLE

Cat gastric smooth muscle strips were used to investigate the involvem ent of protein kinases in the steady-state contraction induced by 1 mu M acetylcholine or 20 mM KCl. The steady-state contraction induced by acetylcholine or KCl was inhibited by EGTA dose dependently. Voltage- dependent Ca2+ channel antagonists dose dependently inhibited the cont ractions induced by KCl as well as by acetylcholine. Inhibitory effect s of voltage-dependent Ca2+ channel antagonists were significantly mor e prominent on KCl-induced contractions than on acetylcholine-induced contractions. The acetylcholine-induced contraction was dose dependent ly inhibited by 8-( N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (T MB-8, a blocker of intracellular Ca2+ release), but the KCl-induced co ntraction was not inhibited at all. Therefore both intracellular Ca2release and extracellular Ca2+ influx seem to be necessary for the ace tylcholine-induced contraction, but intracellular Ca2+ release is not necessary for the KCl-induced contraction. Protein kinase C inhibitors , 10 mu M 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine 2HCl (H-7) a nd 1 mu M staurosporine, significantly inhibited the contraction induc ed by acetylcholine or KCl. Calmodulin antagonists, 30 mu M trifluoper azine and 50 mu M N-(6-aminohexyl)-5-chloro-2-naphthalenesulfonamide H Cl (W-7), however, significantly inhibited the contraction induced by acetylcholine but not by KCl. A tyrosine kinase inhibitor, 50 mu M gen istein, did not affect the acetylcholine-induced contraction but signi ficantly inhibited the KCl-induced contraction. These results strongly suggest that the involvement of protein kinases in regulation of the steady-state contraction may be agonist-dependent. (C) 1997 Elsevier S cience B.V.