Comparison of the changes in cytoplasmic free calcium concentration induced by phenylephrine, vasopressin and angiotensin II in hepatocytes.

Effects of phenylephrine, vasopressin and angiotensin II on cytoplasmic free calcium concentration, [Ca2+]c, were examined by monitoring aequorin bioluminescence in isolated hepatocytes preloaded with aequorin. In the presence of 0.5 mM calcium in the medium, the pattern of changes in aequorin bioluminescence induced by phenylephrine was different from that induced by vasopressin or angiotensin II. When extracellular calcium concentration was reduced to 1 microM, however, these three agents induced identical changes in aequorin bioluminescence. These results suggest that the mode of action of phenylephrine on cytoplasmic free calcium concentration differs from that of either vasopressin or angiotensin II and that the difference in ability to increase calcium influx may account for the distinct patterns induced by these agents.