Effects of vasopressin and La3+ on plasma-membrane Ca2+ inflow and Ca2+ disposition in isolated hepatocytes. Evidence that vasopressin inhibits Ca2+ disposition.
Vasopressin caused a 40% inhibition of 45Ca uptake after the addition of 0.1 mM-45Ca2+ to Ca2+-deprived hepatocytes. At 1.3 mM-45Ca2+, vasopressin and ionophore A23187 each caused a 10% inhibition of 45Ca2+ uptake, whereas La3+ increased the rate of 45Ca2+ uptake by Ca2+-deprived cells. Under steady-state conditions at 1.3 mM extracellular Ca2+ (Ca2+o), vasopressin and La3+ each increased the rate of 45Ca2+ exchange. The concentrations of vasopressin that gave half-maximal stimulation of 45Ca2+ exchange and glycogen phosphorylase activity were similar. At 0.1 mM-Ca2+o, La3+ increased, but vasopressin did not alter, the rate of 45Ca2+ exchange. The results of experiments performed with EGTA or A23187 or by subcellular fractionation indicate that the Ca2+ taken up by hepatocytes in the presence of La3+ is located within the cell. The addition of 1.3 mM-Ca2+o to Ca2+-deprived cells caused increases of approx. 50% in the concentration of free Ca2+ in the cytoplasm [( Ca2+]i) and in glycogen phosphorylase activity. Much larger increases in these parameters were observed in the presence of vasopressin or ionophore A23187. In contrast with vasopressin, La3+ did not cause a detectable increase in glycogen phosphorylase activity or in [Ca2+]i. It is concluded that an increase in plasma membrane Ca2+ inflow does not by itself increase [Ca2+]i, and hence that the ability of vasopressin to maintain increased [Ca2+]i over a period of time is dependent on inhibition of the intracellular removal of Ca2+.
D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007811:Lanthanum / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D006005:Phosphorylases / Q000378:metabolism; D051381:Rats; D013050:Spectrometry, Fluorescence
D002132:Calcium Radioisotopes; D001127:Arginine Vasopressin; D000001:Calcimycin; D004533:Egtazic Acid; D007811:Lanthanum; D006005:Phosphorylases; D002118:Calcium