Divergent pharmacological effects of three calmodulin antagonists, N- (6-aminohexyl) -5-chloro-1-naphthalenesulfonamide (W-7) , chlorpromazine and calmidazolium, on isometric tension development and myosin light chain phosphorylation in intact bovine tracheal smooth muscle
Asano, M.
Journal of Pharmacology and Experimental Therapeutics 251(2): 764-773
1989
ISSN/ISBN: 0022-3565 PMID: 2810127 Document Number: 341697
To investigate the usefulness of calmodulin antagonists in intact cell systems, effects of three calmodulin antagonists, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), chlorpromazine (CPZ) and calmidazolium on isometric tension development and myosin light chain (P-LC) phosphorylation in bovine tracheal smooth muscle strips were compared to inhibition of purified myosin light chain kinase activity. These antagonists inhibited the Ca++. calmodulin-induced activation of myosin light chain kinase in a concentration-dependent manner, with IC50 values of 1.0 (calmidazolium), 25 (W-7) and 65 .mu.M (CPZ), respectively. Inhibitory effects of these antagonists were abolished with increasing concentrations of calmodulin. However, when these antagonists were used in intact smooth muscle trips, the gradation of potencies did not parallel the anticalmodulin activities. W-7 (100 .mu.M) exhibited a similar extent of antagonism between the contractile responses to carbachol and KCl. The increase in P-LC phosphate content in response to 1-min stimulation with 10-5 M carbachol was inhibited by W-7. CPZ exhibited an unexpectedly potent antagonism on carbachol-induced isometric tension development and P-LC phoshorylation. Atropine showed an antagonism similar to CPZ. CPZ and verapamil had similar antagonistic effects on KCl-induced contractions. Calmidozolium (50 .mu.M) produced no significant inhibition on carbachol-induced isometric tension development and P-LC phosphorylation in intact smooth muscle strips. It may be concluded that 1) W-7 antagonizes the smooth muscle contraction through the inhibition of the initial increase in the P-LC phosphorylation; 2) CPZ produces effects other than calmodulin antagonism; and 3) calmidazolium is not effective in intact smooth muscle strips. Thus, only W-7 appears to be a useful calmodulin antagonist in intact tracheal smooth muscle strips.