Participation of Ca2+ channel in liver calcium regulation by calcitonin in rats.

A possible regulatory role of calcitonin (CT) upon liver calcium content was investigated by using a Ca2+ channel blocker in thyroparathyroidectomized (TPTX) rats. In bile duct-ligated TPTX rats, liver calcium content was not significantly increased by a single ip injection of calcium chloride (4.0 mg Ca2+/100 g body weight). Administration of CT (80 MRC mU/100 g) caused a remarkable elevation of liver calcium content. This hormonal effect was inhibited by administration of verapamil (1.0 mg/100 g) or lanthanum chloride (0.4 mg/100 g), Ca2+ channel blockers. CT administration markedly increased the transport of calcium into the bile through the liver cells of TPTX rats injected ip with calcium. This increase in the bile calcium content was prevented by administration of verapamil or lanthanum chloride. Administration of epinephrine (10 micrograms/100 g), vasopressin (10 micrograms/100 g), or concanavalin A (1.0 mg/100 g) produced a significant elevation of bile calcium content; these elevations were not significantly altered by addition of verapamil (1.0 mg/100 g). These data suggest the presence of CT receptors on liver cell plasma membranes which are involved in regulation of membrane Ca2+ channels. It is proposed that CT facilitates the entry of extracellular calcium into liver cells by opening Ca2+ channels located on their plasma membranes.