Membrane depolarization in pc12 cells during hypoxia is regulated
by an o2-sensitive k+ current.
Zhu, Wylie H., Laura Conforti, Maria F. Czyzyk-Krzeska, and David E.
Millhorn.
Department of Molecular and Cellular Physiology, College of
Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0576,
USA
APStracts 3:0058C, 1996.
The effects of hypoxia on potassium current (IK), resting membrane
potential and cytosolic free Ca2+ in rat pheochromocytoma (PC12)
cells were studied. Whole-cell voltage- and current-clamp experiments
were performed to measure IK and membrane potential, respectively.
Cytosolic free Ca2+ level was measured using the Ca2+-sensitive
fluorescent dye fura-2. Depolarizing voltage steps to +50 mV from a
holding potential of -90 mV elicited a slowly inactivating,
tetraethylammonium chloride-sensitive and Ca2+-insensitive IK that
was reversibly inhibited by reduced oxygen tension. Graded reduction
in Po2 (from 150 to 0 mmHg) induced a graded inhibition of an O2
-sensitive IK (IKo2) up to 46 % at 0 mmHg. Moreover, hypoxia induced a
19 mV membrane depolarization, and a two fold increase in cytosolic
free Ca2+. In Ca2+-free condition, inhibition of IKo2 induced a 8 mV
depolarization, suggesting that inhibition of IKo2 was responsible
for initiating depolarization. The effect of reduced Po2 on the
current-voltage relationship showed a reduction of outward current
and a 14 mV shift in the reversal potential comparable to the amount
of depolarization measured in current clamp experiments. Neither Ca
-activated IK nor inwardly-rectifying IK are responsible for the
hypoxia-induced depolarization. In conclusion, PC12 cells express an
O2-sensitive K+ current, inhibition of which leads to membrane
depolarization and increased intracellular Ca2+, making PC12 clonal
cell line a useful model for studying the molecular and biophysical
mechanisms that mediate O2 chemosensitivity.
Received 17 July 1995; accepted in final form 2 February 1996.
APS Manuscript Number C427-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 24 February 96