K+ and cl- ions contribute to the resting membrane conductance of
cultured porcine endocardial endothelial cells.
Fransen, Paul, and Stanislas U. Sys.
Laboratory of Physiology, University of Antwerp (RUCA),
Groenenborgerlaan 171, B-2020 Antwerp, Belgium
APStracts 3:0494H, 1996.
The conventional whole-cell patch clamp technique was used to measure
the resting membrane conductance and membrane currents of single,
non-stimulated, cultured, endocardial endothelial cells of the
porcine right ventricle in different ionic conditions. All cells
displayed the barium-sensitive, inwardly rectifying, potassium (K+)
current, IKi. In 65% of the cells, IKi was the predominant membrane
current. The mean zero-current potential (V0) was -61.0 +/- 12.5 mV
(SD, n = 45). In 35% of the cells, IKi was superposed on an outwardly
rectifying (OR) current. V0 of these cells was more depolarized (
-33.5 +/- 22.0 mV, SD, n = 26). High intracellular Cl- (122 instead of
52 mmol/l) activated or increased the OR current and shifted V0 in
the direction of VCl. In cells displaying the OR current, V0 was
dependent on extracellular Cl-, indicating the contribution of an OR
Cl- current in setting V0. At low intracellular Cl- (6 instead of 52
mmol/l), the OR current was decreased and V0 shifted in the direction
of VK. In cells not displaying the OR current, V0 was dependent on
extracellular K+, but not on Cl-, indicating major permeability to K+
ions in these conditions. Block of the OR current by the Cl- channel
blockers anthracene-9-carboxylic acid (1 mmol/l), flufenamic acid
(100 - 500 [mu]mol/l) and Zn2+ (100 - 200 [mu]mol/l) provided further
evidence for the anionic nature of the OR current. After inhibition
of IKi and the outwardly rectrifying Cl- current, a third current
component was observed in 50% of the cells. The pharmacology and
voltage-dependence of the current suggested the presence of Ca2+
-activated K+ channels in endocardial endothelial cells. From the
present study, it is concluded that the resting membrane conductance
of non-stimulated endocardial endothelial cells is mainly determined
by the combined activity of inwardly rectifying K+, outwardly
rectifying Cl- and Ca2+-activated K+ channels.
Received 26 June 1996; accepted in final form 15 November 1996.
APS Manuscript Number H567-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996