The amiloride-sensitive epithelial na+ channel: binding sites and
channel densities.
Blazer-Yost, Bonnie L., Sandy I. Helman.
Department of Biology, Indiana University- Purdue University at
Indianapolis, and VA Medical Center, Indianapolis, Indiana 46202,
Department of Molecular and Integrative Physiology, University of
Illinois at Urbana-Champaign
APStracts 3:0387C, 1996.
The amiloride-sensitive Na+ channel found in many transporting
epithelia plays a key role in regulating salt and water homeostasis.
Both biochemical and biophysical approaches have been used to
identify, characterize and quantitate this important channel. Among
biophysical methods, there is agreement as to the single channel
conductance and gating kinetics of the highly selective Na+ channel
found in native epithelia. Amiloride and its analogs inhibit
transport through the channel by binding to high affinity ligand
binding sites. This characteristic of high affinity binding has been
used biochemically to quantitate channel densities and to isolate
presumptive channel proteins. Although the goals of biophysical and
biochemical experiments are the same in elucidating mechanisms
underlying regulation of Na+ transport, our review highlights a major
quantitative discrepancy between methods in estimation of channel
densities involved in transport. As the density of binding sites
measured biochemically is three to four orders of magnitude in excess
of channel densities measured biophysically, it is unlikely that high
affinity ligand binding can be used physiologically to quantitate
channel densities and characterize the channel proteins.
Received 19 September 1996; accepted in final form 21 November
1996.
APS Manuscript Number C542-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996