Inward rectifier k+ currents in smooth muscle cells from rat
coronary arteries: block by mg2+, ca2+, and ba2+ ions.
Robertson, Blair E., Adrian D. Bonev, and Mark T. Nelson.
Department of Pharmacology, The University of Vermont, 55A South
Park Drive, Colchester, Vermont 05446, USA
APStracts 3:0014H, 1996.
Inward rectifier potassium channels have been implicated in the
control of membrane potential and external potassium-induced
dilations of small coronary arteries. To identify and characterize
inward rectifier K+ currents in coronary artery smooth muscle, whole
cell K+ currents in smooth muscle cells enzymatically isolated from
rat coronary (septal) arteries (diameters, 100-150 microns) were
measured in the conventional and perforated configurations of the
patch clamp technique. Barium-sensitive, whole cell K+ current
-voltage relationships exhibited inward rectification. Blockers of
calcium-activated K+ channels (1 mM TEA+), ATP-sensitive K+ channels
(10 [mu]M glibenclamide) and voltage-dependent K+ channels (1 mM 4
-aminopyridine) in smooth muscle were without affect on inward
rectifier K+ currents. The non-selective K+ channel inhibitor,
phencyclidine (100 [mu]M) reduced inward rectifier K+ currents by
about 50%. External barium reduced inward currents, with membrane
potential hyperpolarization increasing inhibition. The half
-inhibition constant for barium was 2.1 [mu]M at -60 mV, decreasing e
-fold for a 25 mV hyperpolarization. External cesium also blocked
inward rectifier K+ currents, with the half-inhibition constant for
cesium of 2.9 mM at -60 mV. External calcium and magnesium reduced
inward rectifier K+ currents. At -60 mV, calcium and magnesium (1 mM)
reduced inward currents by 33% and 21%, respectively. Inward
rectification was not affected by dialysis of the cell's interior
with a nominally calcium- and magnesium-free solution. These findings
indicate that inward rectifier K+ channels exist in coronary artery
smooth muscle and that barium may be a useful probe for the
functional role of inward rectifier K+ channels in coronary arteries.
Received 6 April 1995; accepted in final form 12 December 1995.
APS Manuscript Number H336-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96