Abstract
Effects of several organic Ca antagonists and putative calmodulin antagonists on the release of 3H-norepinephrine from rabbit aorta were examined. 65.4mM K solution increased the 3H-efflux from the aorta previously loaded with 3H-norepinephrine, and the increment was inhibited by removing Ca in the medium. Verapamil, D600, N-(6-aminohexyl)-5-chioro-l-naphthalenesulphonamide (W-7), and N2-dansyl-L-arginine-4-t-butyIpiperidine amide (Tl 233), in the concentration of 10-5M, did not inhibit the 65.4mM K-induced increase in the 3H-efflux. Verapamil rather potentiated the efflux. High concentration (2 X 10-4M) of verapamil and W-7 increased the 3H-efflux. The increment was not dependent on external Ca. 65.4mM K, added in the presence of 2 X 10-4M verapamil or W-7, did not produce further increase in the 3H-efflux. D600, diltiazem, prenylamine and Tl 233, in the concentration of 2 X 10-4M, also increased the 3H-efflux. From these results, it is suggested that adrenergic nerve terminals are relatively insensitive to the inhibitory effects of organic Ca antagonists and calmodulin antagonists and that high concentration of these inhibitors themselves release norepinephrine by a mechanism independent of external Ca.
Published Version
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