Oxygen availability modulates transmembrane ca2+-flux via second
messenger pathways in anoxia-tolerant hepatocytes.
Land, S. C., R. H. Sanger, and P. J. S. Smith.
Biocurrents Research Center, Marine Biological Laboratory, Woods
Hole, MA 02543, U.S.A.
APStracts 3:0500A, 1996.
Transmembrane Ca2+-flux was studied from single isolated turtle
hepatocytes using a non-invasive Ca2+-selective self-referencing
microelectrode. Cells in Ca2+-reduced culture medium demonstrated a
vanadate and lanthanum inhibitable Ca2+-efflux of 4 x10-17 mol
Ca2+.[mu][mu]-2.sec-1 continuously over 170h. This flux diminished
with 50nM 12-O-tetradecanoylphorbol-13-acetate, a protein kinase-C
(PK-C) activator, and was reinstated on PK-C de-activation with
sphingosine. Progressive hypoxia resulted in a reversible suppression
of Ca2+-efflux to 90% of normoxic controls with an apparent KmO2 of
145[mu]M. PK-C 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. 100[mu]M adenosine
elevated Ca2+-efflux 2-fold in normoxia, but neither adenosine nor
the A1 purinoreceptor antagonist, 8-phenyltheophylline altered the
observed aerobic suppression. Aerobic administration of 2-10mM KCN
failed to reproduce the anaerobic suppression, however, in
conjunction with 10mM 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.
Received 4 March 1996; accepted in final form 25 October 1996.
APS Manuscript Number A213-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996