Functional coupling of na-k-2cl cotransport and ca2+-dependent k+
channels in vascular endothelial cells.
O'neill, W. Charles, and Daniel F. Steinberg.
Renal Division, Department of Medicine and Department of
Physiology, Emory University School of Medicine
APStracts 2:0161C, 1995.
To determine whether the activation of Na-K-2Cl cotransport by Ca2+
-mobilizing agonists is a direct effect of Ca2+ or is secondary to
activation of Ca2+-dependent K+ channels (via cell shrinkage or
decreased intracellular [Cl-]) we measured K+ fluxes in aortic
endothelial cells in response to ATP and bradykinin. With either
agonist there was an immediate, bumetanide-insensitive efflux
inhibitable by the K+ channel blockers tetrabutylammonium (TBA, 23
mM) and quinidine (1 mM), followed several minutes later by increased
bumetanide-sensitive efflux or influx (Na-K-2Cl cotransport). ATP
induced a loss of cell K+ that was prevented by TBA and augmented by
bumetanide. Both TBA and quinidine prevented the stimulation of
cotransport by agonists but not by hypertonic shrinkage. Raising
medium [K+] to prevent K+ loss also blocked activation of cotransport
by agonists. The results indicate that the stimulation of Na-K-2Cl
cotransport by Ca2+ is not direct, but instead is indirect via
activation of Ca2+-dependent K+ channels and a resulting decrease in
cell volume and intracellular [Cl-]. This suggests that at least one
role of Na-K-2Cl cotransport in endothelial cells is to maintain cell
volume and intracellular [Cl-] during agonist stimulation.
Received 27 December 1994; accepted in final form 21 March 1995.
APS Manuscript Number C774-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 April 1995.