The Journal of General Physiology
Cell MicroControls
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Published online January 14, 2008
doi:10.1085/jgp.200709875
The Journal of General Physiology, Vol. 131, No. 2, 125-135
The Rockefeller University Press, 0022-1295 $30.00
© 2008 Ledoux et al.
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ARTICLE

 Ca2+-activated K+ Channels in Murine Endothelial Cells: Block by Intracellular Calcium and Magnesium



Jonathan Ledoux, Adrian D. Bonev, and Mark T. Nelson

Department of Pharmacology, College of Medicine, University of Vermont, Burlington, VT 05405

Correspondence to Mark T. Nelson: mark.nelson{at}uvm.edu

The intermediate (IKCa) and small (SKCa) conductance Ca2+-sensitive K+ channels in endothelial cells (ECs) modulate vascular diameter through regulation of EC membrane potential. However, contribution of IKCa and SKCa channels to membrane current and potential in native endothelial cells remains unclear. In freshly isolated endothelial cells from mouse aorta dialyzed with 3 µM free [Ca2+]i and 1 mM free [Mg2+]i, membrane currents reversed at the potassium equilibrium potential and exhibited an inward rectification at positive membrane potentials. Blockers of large-conductance, Ca2+-sensitive potassium (BKCa) and strong inward rectifier potassium (Kir) channels did not affect the membrane current. However, blockers of IKCa channels, charybdotoxin (ChTX), and of SKCa channels, apamin (Ap), significantly reduced the whole-cell current. Although IKCa and SKCa channels are intrinsically voltage independent, ChTX- and Ap-sensitive currents decreased steeply with membrane potential depolarization. Removal of intracellular Mg2+ significantly increased these currents. Moreover, concomitant reduction of the [Ca2+]i to 1 µM caused an additional increase in ChTX- and Ap-sensitive currents so that the currents exhibited theoretical outward rectification. Block of IKCa and SKCa channels caused a significant endothelial membrane potential depolarization ({approx}11 mV) and decrease in [Ca2+]i in mesenteric arteries in the absence of an agonist. These results indicate that [Ca2+]i can both activate and block IKCa and SKCa channels in endothelial cells, and that these channels regulate the resting membrane potential and intracellular calcium in native endothelium.

Abbreviations used in this paper: AEC, aortic endothelial cell; Ap, apamin; BKCa, large conductance Ca2+-activated potassium channel; [Ca2+]i, intracellular Ca2+ level; ChTX, charybdotoxin; EC, endothelial cell; EDHF, endothelium-derived hyperpolarizing factor; EK, equilibrium potential; GHK, Goldman-Hodgkin-Katz; IbTX, iberiotoxin; IKCa, intermediate conductance Ca2+-activated potassium channel; Kir, inward rectifier potassium channel; Kv, voltage-dependent potassium channel; SKCa, small conductance Ca2+-activated potassium channel; TRP, transient receptor potential.


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