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Am J Physiol Cell Physiol 252: C128-C137, 1987;
0363-6143/87 $5.00
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AJP - Cell Physiology, Vol 252, Issue 2 C128-C137, Copyright © 1987 by American Physiological Society

ARTICLES

Blocking agents of Ca2+-activated K+ channels in cultured medullary thick ascending limb cells

S. E. Guggino, W. B. Guggino, N. Green and B. Sacktor

Ca2+-activated K+ channels with estimated single channel conductances of 127 +/- 2 pS were identified in the apical cell membrane of clone A3 of cultured medullary thick ascending limb (MTAL) cells. Both Ba2+ and the scorpion toxin, charybdotoxin (CTX), are slow blockers of the channels. An application of 0.1 microM Ba2+ to the intracellular face caused a 50% reduction in fractional open time (fv). Ba2+ block is both concentration and voltage dependent. Concentrations of CTX as low as 2 nM in the extracellular solution caused a significant reduction in fv. Tetraethylammonium (TEA) and quinine are fast blockers of Ca2+-activated K+ channels in MTAL cells. TEA, 400 microM, in the extracellular solution caused a voltage-dependent reduction in channel amplitude, whereas it takes 10 mM in the intracellular solution to reduce channel amplitude by 30%. Micromolar amounts of quinine applied to the intracellular face caused the channels to flicker rapidly between open and blocked states. These results suggest that K+ channels in MTAL cells are homologous to those found in muscle cells, and that these blocking agents may be used to probe the nature of K+ conductances in several nephron segments.


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