Effect of extracellular Ca2+ on plasma membrane Ca2+ inflow and cytoplasmic free Ca2+ in isolated hepatocytes.
An initial rapid phase and a subsequent slow phase of 45Ca2+ uptake were observed following the addition of 45Ca2+ to Ca2+-deprived hepatocytes. The magnitude of the rapid phase increased 15-fold over the range 0.1-11 mM extracellular Ca2+ (Ca2+o) and was a linear function of [Ca2+]o. The increases in the rate of 45Ca2+ uptake were accompanied by only small increases in the intracellular free Ca2+ concentration. In cells made permeable to Ca2+ by treatment with saponin, the rate of 45Ca2+ uptake (measured at free Ca2+ concentrations equal to those in the cytoplasm of intact cells) increased as the concentration of saponin increased from 1.4 to 2.5 micrograms per mg wet weight cells. Rates of 45Ca2+ uptake by cells permeabilized with an optimal concentration of saponin were comparable with those of intact cells incubated at physiological [Ca2+o], but were substantially lower than those for intact cells incubated at high [Ca2+o]. It is concluded that Ca2+ which enters the hepatocyte across the plasma membrane is rapidly removed by binding and transport to intracellular sites and by the plasma membrane (Ca2+ + Mg2+)-ATPase and the plasma membrane Ca2+ inflow transporter is not readily saturated with Ca2+o.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability; D003593:Cytoplasm / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D007811:Lanthanum / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D051381:Rats
D000001:Calcimycin; D007811:Lanthanum; D002118:Calcium