Ca2+-dependent k+ current in arterial smooth muscle cells from
aldosterone-salt hypertensive rats.
Liu, Yu, Allan W. Jones, and Michael Sturek.
Vascular Cell Biophysics Laboratory, Dalton Cardiovascular Research
Center and Department of Physiology, School of Medicine, University
of Missouri, Columbia, MO 65211
APStracts 2:0155H, 1995.
Aorta from aldosterone-salt hypertensive rats (AHR) demonstrates an
increased basal 42K efflux. We investigated the cellular mechanisms
of this alteration by measuring 42K efflux from aortic segments as
well as myoplasmic Ca2+ concentration (Ca+) and K+ current in aortic
smooth muscle cells from AHR and normotensive control-salt rats
(CSR). Both diltiazem and nisoldipine attenuated, but did not
normalize the increase in basal 42K efflux in AHR. The resting Ca+
was elevated in cells from AHR (148+/-15 nM vs. 91+/-12 nM for CSR,
p<0.05). The rate of Mn2+ quenching under basal conditions was also
increased in cells from AHR and the increase was abolished by Cd2+.
However, the resting membrane potential was not different between CSR
and AHR (-49+/-5 mV vs. -50+/-4 mV). The steady-state, whole-cell K+
current was also increased in cells from AHR. This increase was
abolished by charybdotoxin, tetraethylammonium, La3+ and when the Ca+
was clamped at zero or 100 nM with EGTA. The single channel
conductance of the large conductance KCa channels was not altered in
AHR. Further, 33% of cells from AHR versus 1% from CSR showed
spontaneous transient outward K+ currents (STOCs), which reflect
activation of Ca2+-dependent K+ channels by Ca2+ released from
caffeine-sensitive stores. While the acute caffeine-induced Ca+
response was similar between CSR and AHR, the outward current and 42K
efflux responses to caffeine were greater in AHR. After continued
exposure to caffeine, the basal 42K efflux was attenuated more in AHR
than in CSR. Charybdotoxin resulted in a greater depolarization in
AHR cells than CSR cells (9.8+/-2.2 mV vs. 3.5+/-1.6 mV, p<0.05).
These results indicate that the increases in both 42K efflux and K+
current reflect an increased activity of Ca2+-dependent K+ channels,
that is associated with an increased Ca2+ influx and resting Ca+ and
altered Ca handling by the sarcoplasmic reticulum in aortic smooth
muscle cells from AHR.
Received 3 November 1994; accepted in final form 29 March 1995.
APS Manuscript Number H981-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.