Regulation of epithelial na+ channels from m-1 cortical collecting
duct cells .
Chalfant, Michael L., Kim Peterson-Yantorno, Thomas G. O'brien, and
Mortimer M. Civan.
Departments of Physiology and Medicine, and the Graduate Group in
Bioengineering, The University of Pennsylvania, Philadelphia, PA; and
The Lankenau Medical Research Center4, Wynnewood, PA
APStracts 3:0123F, 1996.
The M-1 cell line is derived from the mouse cortical collecting duct
and displays the low-conductance, highly Na+ selective channel
activity of the [alpha][beta][tau]-heterotrimeric ENaC channel. The
short-circuit current (ISC) across M-1 monolayers was 89 +/- 4
[mu]A/cm2 and the transepithelial conductance was 2.1 +/- 0.2 mS/cm2.
ISC was abolished by blocking the Na+ pump with ouabain. Both ISC and
gT were inhibited by benzamil > amiloride >>
dimethylamiloride. Under our experimental conditions, vasopressin,
forskolin and dibutyryl cAMP had no detectable effects on ISC or gT.
Increasing apical Na+ entry with nystatin increased ISC. The possible
regulation of the M-1 Na+ channel by cAMP-activated kinase (PKA) was
further examined with excised inside-out patches. The open-time
probability Po was not fixed, displaying substantial variance.
Perfusion with ATP itself, with the catalytic subunit of PKA with
ATP, or with alkaline phosphatase had no consistent effect on Po, the
unitary current, or the kinetics of the M-1 Na+ channel. The data are
consistent with the concept that PKA stimulates epithelial Na+
channels by phosphorylating a site with access to, but not within the
apical membrane patch during cell-attached and excised-patch studies.
Received 5 April 1996; accepted in final form 2 July 1996.
APS Manuscript Number F109-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996