Inhibitory effects of cicletanine on smooth muscle in comparison to those of nifedipine and sodium nitroprusside.

The inhibitory effect of cicletanine was studied, in comparison to the effects of nifedipine and sodium nitroprusside (SNP), in various types of smooth muscle: portal vein and iliac artery of rabbit; gastric fundus and antrum of rabbit and guinea pig; guinea pig taenia coli and uterus. In all types of tissue the nifedipine-sensitive component (LCA, L-type calcium channel dependent activation) was inhibited by cicletanine (threshold concentration 10(-6) mol/l to 10(-5) mol/l). The nifedipine to resistant component (NLCA) was in some tissues preferentially inhibited by SNP (gastric fundus) and in other tissues preferentially by cicletanine (portal vein), with graded intermediate forms (iliac artery). Consequently, the inhibitory effect of cicletanine on NLCA is different in mechanism to that of SNP. Only papaverine suppressed all types of activation.