Coexistence of two types of ca2+-activated k+ channels in rat renal
arterioles.
Gebremedhin, Debebe, Mary Kaldunski, Elizabeth R. Jacobs, David R.
Harder, Richard J. Roman.
Department of Physiology and Cardiovascular Research Center,
Medical College of Wisconsin, Milwaukee, Wisconsin 53226
APStracts 2:0112F, 1995.
Single-channel K+ currents were characterized in vascular smooth
muscle cells freshly isolated from preglomerular arterioles (15-40
[mu]m o.d.) of the rat. Under conditions of symmetrical K+ (145 mM),
two types of single-channel K+ currents with unitary slope
conductances of 68 +/- 2.6 pS and 251 +/- 4.9 pS were recorded from
excised inside-out membrane patches. The open state probability (NPo)
of these two types of K+ channels was voltage-sensitive and the
channels were highly selective for K+ over Na+. Elevation of [Ca2+]i
from 0.1 to 0.5 [mu]M on the cytoplasmic face of inside-out patches
increased the frequency of opening and the NPo of both the 68 pS and
the 251 pS K+ channels. Application of ATP (0.1-1 mM) to the internal
surface of inside-out patches had no effect on the activities of both
channel types. Internally applied Ba2+ (1 mM) blocked both of these
channels. Externally applied tetraethylammonium (TEA, 0.1 to 0.3 mM)
or charybdotoxin (50 nM) blocked both the 68 pS and the 251 pS K+
channels. Externally applied apamin (50 nM), however, selectively
blocked the 68 pS K+ channel but had no effect on the frequency of
opening of the 251 pS K+ channel. Apamin also reduced macroscopic K+
current recorded from voltage-clamped rat renal arteriolar muscle
cells by 25-30%. These results indicate the coexistence of two types
of Ca2+-activated K+ channels in the membranes of vascular smooth
muscle cell isolated from renal preglomerular arterioles of the rat
which differ in unitary conductances and pharmacological properties.
Received 16 February 1995; accepted in final form 26 June 1995.
APS Manuscript Number F58-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.