Na(+)-Ca2+ exchange in cultured rat hepatocytes: evidence against a role in cytosolic Ca2+ regulation or signaling.
Plasma membrane Na(+)-Ca2+ exchange contributes importantly to the regulation of cytosolic Ca2+ concentration ([Ca2+]i) in excitable cells. Despite extensive study in excitable tissues, the role of this transporter in the regulation of [Ca2+]i in hepatocytes is unknown, and conflicting information has been reported regarding the presence of Na(+)-Ca2+ exchange in hepatocyte plasma membrane vesicles. We have therefore assessed the role of Na(+)-dependent Ca2+ transport in the regulation of [Ca2+]i in rat hepatocytes in primary culture under basal conditions and after exposure to vasopressin, a hormone that elevates [Ca2+]i. Ca2+ efflux, measured using 45Ca, did not differ in the presence or absence of extracellular Na+, either under basal conditions or in response to vasopressin. [Ca2+]i, measured using the Ca2(+)-sensitive dye fura-2, was not altered by transient or prolonged exposure to Na(+)-free media or by exposure to ouabain in concentrations sufficient to produce a five-fold elevation in intracellular Na+ concentration. The [Ca2+]i response to vasopressin was also unaffected by Na+ removal or ouabain. By contrast, in cultured rat cardiac myocytes, cells that possess Na(+)-Ca2+ exchange, transient or prolonged Na+ removal as well as ouabain exposure produced greater than fivefold increases in [Ca2+]i compared with controls. We conclude that Na(+)-Ca2+ exchange does not contribute to the regulation of [Ca2+]i in hepatocytes.
Lidofsky
S D
SD
Department of Medicine, University of California, San Francisco 94143.
Xie
M H
MH
Scharschmidt
B F
BF
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D006706:Homeostasis; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008536:Meglumine / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D014667:Vasopressins / Q000494:pharmacology
D002132:Calcium Radioisotopes; D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D014667:Vasopressins; D010042:Ouabain; D008536:Meglumine; D008094:Lithium; D012964:Sodium; D002118:Calcium