Whole-cell and unitary amiloride-sensitive sodium currents in m-1
mouse cortical collecting duct cells.
Chalfant, Michael L., Thomas G. O'brien, and Mortimer M. Civan.
Lankenau Medical Research Center, Wynnewood, PA; and the Graduate
Group in Bioengineering, and the Departments of Physiology and
Medicine, University of Pennsylvania, Philadelphia, PA 19104
APStracts 2:0354C, 1995.
Amiloride-sensitive whole-cell currents have been reported in M-1
mouse cortical collecting duct cells [Korbmacher, et al., J. Gen.
Physiol., 102:761, 1993]. We have confirmed that amiloride inhibits
the whole-cell currents, but not necessarily the measured whole-cell
conductance. This discrepancy reflects the action of the
transepithelial potential in modifying measured whole-cell currents.
Anomalous responses were eliminated by removing external Na+ and/or
introducing para-epithelial 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 to 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 sodium 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 displaying one
operative channel were best described with > 2 expontential
terms each. We conclude that: (i) study of M-1 whole-cell Na+
currents is facilitated by reducing the transepithelial potential to
zero, (ii) these M-1 currents reflect the operation of Na(5)
channels, and (iii) the Na+ channels display complex kinetics,
involving > 2 open and > 2 closed states.
Received 4 August 1995; accepted in final form 22 September 1995.
APS Manuscript Number C481-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95