AJP - Renal Physiology, Vol 258, Issue 2 244-F253, Copyright © 1990 by American Physiological Society

ARTICLES

A potassium channel in the apical membrane of rabbit thick ascending limb of Henle's loop

W. H. Wang, S. White, J. Geibel and G. Giebisch
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.

We used the patch-clamp technique to study the activity of single potassium channels in the apical membrane of isolated thick ascending limbs of Henle's loop (TAL) of rabbit kidneys. In cell-attached patches with NaCl Ringer or high-K+ solution in the bath and 140 mM K+ in the pipette, an inwardly rectifying K+ channel was observed with an inward slope conductance of 22.0 +/- 0.5 pS and outward slope conductance of 10.2 +/- 0.3 pS at 22 degrees C (n = 15). The channel was highly selective for K+, with a calculated permeability ratio for K(+)-to-Na+ of 20:1 (n = 4). The open probability (Po) of the channel was 0.89 +/- 0.03 (n = 15) and was not voltage dependent. In inside-out patches with 140 mM K+ in both the bath and the pipette solutions, both Po and conductance of the channel were similar to that in cell-attached patches. Addition of 0.1 mM Ba2+ to the pipette solution reduced Po of the channel in a voltage-dependent manner. Lowering the pH of the bath solution from 7.4 to 6.9 or increasing Ca2+ concentration from 0 to 0.5 mM in inside-out patches did not alter either Po or conductance of the channel. Addition of 2 mM ATP to the bath solution completely inhibited channel activity. This ATP-induced inhibition was fully reversible and was found to be dependent on the ratio of ATP to ADP, since adding 1 mM ADP to the bath solution relieved the ATP-induced blockade. The property of this small-conductance K+ channel make it a likely candidate for recycling of K+ across the apical membrane of TAL of the rabbit kidney. ATP and ADP are possible intracellular regulators of the channel's activity.

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