EFFECTS OF CALMODULIN ANTAGONISTS ON TENSION AND CELLULAR CALCIUM CONTENT IN DEPOLARIZED VASCULAR AND INTESTINAL SMOOTH MUSCLES

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Abstract
1 Several putative calmodulin antagonists have been examined for their inhibitory action on muscle tension and cellular Ca content in the K-depolarized vascular and intestinal smooth muscles. 2 The 65.4 mm K-induced sustained contraction in the media-intimal layer of rabbit aorta and the 45.4 mm K-induced sustained contraction in guinea-pig taenia coli were inhibited by the calmodulin antagonists, prenylamine, chlorpromazine, N2-dansyl-l-argiiiine-4-t-butylpiperadine amide (No. 233), and N-(6-aminohexyl)-5-chloro-l-naphthalenesulphonamide (W-7), and also by the organic Ca antagonists, verapamil and diltiazem. 3 The cellular Ca content in rabbit aorta and guinea-pig taenia coli as measured by a modified lanthanum technique increased in the high-K solutions. The increments were inhibited by these antagonists at concentrations similar to those required to inhibit the K-induced contractions. However, W-7 did not change (in aorta) or only slightly decreased (in taenia coli) the K-induced increase in the cellular Ca content. 4 A high concentration (2 × 10−4m) of W-7 increased the resting cellular Ca content without increasing the muscle tension in aorta. The increment was inhibited by verapamil, sodium nitroprus-side or hypoxia (N2 aeration). 5 It is suggested that the inhibitory effects of prenylamine, chlorpromazine and No. 233 may be attributed mainly to the Ca antagonistic effect whereas W-7 may inhibit the process beyond the transmembrane Ca influx.

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