Journal of Applied Physiology AJP: Cell Physiology
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J Appl Physiol 82: 776-783, 1997;
8750-7587/97 $5.00
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Journal of Applied Physiology
Vol. 82, No. 3, pp. 776-783, March 1997
ENVIRONMENT

O2 availability modulates transmembrane Ca2+ flux via second-messenger pathways in anoxia-tolerant hepatocytes

S. C. Land, R. H. Sanger, and P. J. S. Smith

Biocurrents Research Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543

Received 4 March 1996; accepted in final form 25 October 1996.

Land, S. C., R. H. Sanger, and P. J. S. Smith. O2 availability modulates transmembrane Ca2+ flux via second-messenger pathways in anoxia-tolerant hepatocytes. J. Appl. Physiol. 82(3): 776-783, 1997.---Transmembrane Ca2+-flux was studied from single isolated turtle hepatocytes by using a noninvasive Ca2+-selective self-referencing microelectrode. Cells in Ca2+-reduced culture medium demonstrated a vanadate-and lanthanum-inhibitable Ca2+-efflux of 4 × 10-17 mol Ca2+ · µm-2 · s-1 continuously over 170 h. This flux diminished with 50 nM phorbol 12-myristate 13-acetate, a protein kinase C (PKC) activator, and was reinstated on PKC deactivation with sphingosine. Progressive hypoxia resulted in a reversible suppression of Ca2+ efflux to 90% of normoxic controls with an apparent Michaelis constant for oxygen of 145 µM. PKC activation was critical in this suppression, as anaerobic administration of sphingosine caused a Ca2+ influx and cell rupture. Hypoxia was also associated with an altered pattern of adenosine-mediated control over Ca2+ efflux. Adenosine (100 µM) elevated Ca2+ efflux twofold in normoxia, but neither adenosine nor the A1-purinoreceptor antagonist 8-phenyltheophylline altered the observed anaerobic suppression. Aerobic administration of 2-10 mM KCN failed to reproduce the anaerobic suppression; however, in conjunction with 10 mM iodoacetate, complete metabolic blockade caused a Ca2+ influx and cell rupture. These observations suggest modulatory control by oxygen over transmembrane Ca2+ efflux involving second-messenger systems in the hypoxic transition.

oxygen sensing; hypometabolism; adenosine; protein kinase C; calcium homeostasis; calcium-selective self-referencing probe

0161-7567/97 $5.00 Copyright © 1997 the American Physiological Society




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