EFFECT OF PINAVERIUM AND OTHER CALCIUM-CHANNEL BLOCKERS ON CONTRACTION OF ISOLATED GASTRIC ANTRAL SMOOTH-MUSCLE CELLS CAUSED BY GASTROINTESTINAL HORMONES

Gastrointestinal hormones,gastrin, cholecystokinin (CCK), and motilin, are known to induce contraction of digestive smooth muscle cells from various species. In this paper, we studied the effect of calcium channel blockers, diltiazem, nicardipine, and pinaverium on the hormone-dependent contraction of smooth muscle cells isolated from rabbit antrum. Gastrin, CCK-8, and motilin caused dose-dependent contraction with EC-50 values in the physiological range (10-100 pM). This contractile effect was dependent upon extracellular calcium for gastrin and CCK-8 but not for motilin. When used alone, calcium channel blockers diltiazem, nicardipine, but not pinaverium, caused a weak but significant contraction of the cells. Pinaverium inhibited both gastrin- and CCK-8-induced contractions with IC-50 values of 1 nM and it was much less potent in the inhibition of motilin-induced contractions (IC-50 = 25 nM). The effect of pinaverium was equivalent to that of diltiazem in the inhibition of CCK-8- or gastrin-induced contractions. Both drugs were slightly more potent than nicardipine (IC-50 = 10 nM versus 1 nM for pinaverium and 5 nM for diltiazem). In contrast, diltiazem and pinaverium were less potent against motilin stimulation, diltiazem being 5 times more potent than pinaverium. In conclusion, it appears that since Ca2+ antagonists pinaverium, diltiazem and nicardipine inhibited contraction of smooth muscle cells stimulated by gastrointestinal hormones, ''L-type'' calcium channels of the plasma membrane might,also be regulated through occupation of gastrin or CCK receptors.