A mitochondrial uncoupler increases kca currents but decreases kv
currents in pulmonary artery smooth muscle cells.
Yuan, Xiao-Jian, Takao Sugiyama, William F. Goldman, Lewis J. Rubin,
and Mordecai P. Blaustein.
Department of Medicine, Division of Pulmonary and Critical Care
Medicine, and Department of Physiology, University of Maryland School
of Medicine, and Geriatric Research, Education, and Clinical Center,
Baltimore Veterans Affairs Medical Center, Baltimore, Maryland
21201
APStracts 2:0278C, 1995.
Intracellular free Ca2+ ([Ca2+]i) and ATP play important roles in the
regulation of K+ channels in pulmonary artery (PA) myocytes. Previous
studies have demonstrated that hypoxia and the metabolic inhibitor,
2-deoxy-D-glucose, decrease voltage-gated K+ (KV) currents (IK(V))
and thereby depolarize PA myocytes; these effects lead to a rise in
[Ca2+]i. Here, we used FCCP, a protonophore that uncouples
mitochondrial respiration from ATP production, to test whether the
inhibition of oxidative phosphorylation affects K+ channel activities
in rat PA myocytes. Patch clamp and fluorescent imaging microscopy
techniques were used to measure K+ currents (IK) and [Ca2+]i,
respectively. FCCP (3-5 [mu]M) reversibly raised [Ca2+]i in the
presence and absence of external Ca2+. This effect was prevented by
pretreating the cells with the membrane-permeable Ca2+ chelator,
BAPTA-AM. This suggests that much of the FCCP-evoked rise in [Ca2+]i
was due to Ca2+ release from intracellular stores. Brief exposure to
FCCP (2 min) reversibly enhanced IK. This augmentation was not
influenced by glibenclamide, an ATP-sensitive K+ channel blocker, but
was eliminated by pretreatment with BAPTA-AM. This implies that the
FCCP-evoked rise in [Ca2+]i activated Ca2+-activated (KCa) channels.
Furthermore, in BAPTA-treated cells, longer application (>/=6 min) of
FCCP reversibly decreased IK(V) in PA cells bathed in Ca2+-free
solution. These results demonstrate that FCCP affects KCa and KV
channels by different mechanisms. FCCP increases IK(Ca) by raising
[Ca2+]i primarily as a result of Ca2+ release, but decreases IK(V) by
a Ca2+-independent mechanism, presumably the inhibition of oxidative
ATP production.
Received 2 February 1995; accepted in final form 14 July 1995.
APS Manuscript Number C63-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.