Mechanisms of spasmolytic action of bile salts in depolarized guinea-pig taenia coli.

The effects of bile salts on the calcium movements and the electrical activity of the guinea-pig taenia coli were investigated and compared with those of papaverine in order to explore the mechanisms of their spasmolytic action. Four bile salts, deoxycholate, chenodeoxycholate, ursodeoxycholate and cholate, as well as papaverine, dose-dependently relaxed the depolarized taenia coli. The bile salts and papaverine caused the acceleration of 45Ca-efflux with the synchronous muscle relaxation and inhibited the cellular 45Ca-uptake by the depolarized muscle preparation. The bile salts also inhibited the increased spike frequency and the developed tension in the depolarized taenia coli. Furthermore, the dose-relaxation curves for bile salts were shifted to the right as the external calcium ion was increased. These findings suggest that the bile salts, like papaverine, may exert their spasmolytic action through accelerating the Ca-efflux and inhibiting the Ca-influx of the smooth muscle cells.