Effect of external sodium and calcium on calcium efflux in arteria carotis of cattle.

The dependence of the 45Ca-efflux from the smooth muscle cells of the arteria carotis of cattle on external sodium and calcium was studied. In the absence of external calcium the replacement of NaCl by sucrose leads to a decreased 45Ca-efflux rate, replacement by LiCl to an increased efflux rate. With regard to the presence of sodium and calcium in the external medium, the 45Ca-efflux rate decreases in the following order: Na + Ca less than less than Na + Ca-free less than Na-free (Na substituted by sucrose) + Ca-free. LiCl considerably stimulates the 45Ca-efflux rate in the presence of external calcium. An inhibition of the Na, K-ATPase activity lasting for more than 20 min leads to a decrease of the 45Ca-efflux rate. The results obtained suggest the existence of a Na-Ca-exchange in the arteria carotis of cattle.