Cyclic nucleotide gated cation channels mediate sodium absorption
by inner medullary collecting duct (mimcd-k2) cells.
Vandorpe, David H., Flora Ciampolillo, Ryan B. Green, and Bruce A.
Stanton.
Department of Physiology, Dartmouth Medical School, Hanover, NH,
03755
APStracts 3:0334C, 1996.
The inner medullary collecting duct cell line, mIMCD-K2, absorbs
sodium (Na+) by an amiloride-sensitive, electrogenic mechanism
(18,19). The goal of the present study was to characterize the
amiloride-sensitive, Na+-conducting channels responsible for
electrogenic Na+ absorption. To this end we measured Na+ currents in
single cells using the patch clamp technique and Na+ currents across
monolayers mounted in Ussing-type chambers. In whole-cell patch clamp
experiments, amiloride-sensitive, inward Na+ currents were mediated
by non-selective cation channels. In single-channel patch clamp
experiments, amiloride and cGMP-sensitive, 20 pS non-selective cation
channels (i.e., CNG channels) were identified in the apical membrane.
CNG channels were inhibited by amiloride, diltiazem, EIPA, and 8-Br
-cGMP and were permeable to Ca++ and Mg++. ENaC-like Na+ channels were
never observed in whole-cell or single-channel recordings. Na+
absorption across confluent monolayers was inhibited with a rank
order potency of benzamil > amiloride > phenamil
>> EIPA > diltiazem. Our data are most
consistent with the view that CNG channels mediate electrogenic Na+
absorption across mIMCD-K2 cells.
Received 30 May 1996; accepted in final form 11 October 1996.
APS Manuscript Number C301-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996