Am J Physiol Cell Physiol AJP: Gastrointestinal and Liver Physiology
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Am J Physiol Cell Physiol 270: C998-C1010, 1996;
0363-6143/96 $5.00
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AJP - Cell Physiology, Vol 270, Issue 4 C998-1010, Copyright © 1996 by American Physiological Society

ARTICLES

Whole cell and unitary amiloride-sensitive sodium currents in M-1 mouse cortical collecting duct cells

M. L. Chalfant, T. G. O'Brien and M. M. Civan
Lankenau Medical Research Center, Wynnewood 19096, USA.

Amiloride-sensitive whole cell currents have been reported in M-1 mouse cortical collecting duct cells (Korbmacher et al., J. Gen. Physiol. 102: 761-793, 1993). We have confirmed that amiloride inhibits the whole cell currents but not necessarily the measured whole cell currents. Anomalous responses were eliminated by removing external Na+ and/or introducing paraepithelial shunts. The amiloride-sensitive whole cell currents displayed Goldman rectification. The ionic selectivity sequence of the amiloride-sensitive conductance was Li+ > Na+ >> K+. Growth of M-1 cells on permeable supports increased the amiloride-sensitive whole cell permeability, compared with cells grown on plastic. Single amiloride-sensitive channels were observed, which conformed to the highly selective low-conductance amiloride-sensitive class [Na(5)] of epithelial Na+ channels. Hypotonic pretreatment markedly slowed run-down of channel activity. The gating of the M-1 Na+ channel in excised patches was complex. Open- and closed-state dwell-time distributions from patches that display one operative channel were best described with two or more exponential terms each. We conclude that 1) study of M-1 whole cell Na+ currents is facilitated by reducing the transepithelial potential to zero, 2) these M-1 currents reflect the operation of Na(5) channels, and 3) the Na+ channels display complex kinetics, involving > or = 2 open and > or = 2 closed states.


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