AJP - Gastrointestinal and Liver Physiology, Vol 259, Issue 1 56-G61, Copyright © 1990 by American Physiological Society

ARTICLES

Na(+)-Ca2+ exchange in cultured rat hepatocytes: evidence against a role in cytosolic Ca2+ regulation or signaling

S. D. Lidofsky, M. H. Xie and B. F. Scharschmidt
Department of Medicine, University of California, San Francisco 94143.

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.

This article has been cited by other articles:

				A. KOVACS, M. R. COURTOIS, B. BARZILAI, I. E. KARL, P. A. LUDBROOK, and R. S. HOTCHKISS Reversal of Hypocalcemia and Decreased Afterload in Sepsis . Effect on Myocardial Systolic and Diastolic Function Am. J. Respir. Crit. Care Med., December 1, 1998; 158(6): 1990 - 1998. [Abstract] [Full Text] [PDF]