The role of actin in regulation of epithelial sodium channels by
cftr.
Ismailov, Iskander I., Bakhram K. Berdiev, Vadim Gh. Shlyonsky,
Catherine M. Fuller, Adriana G. Prat, Biljana Jovov, Horacio F.
Cantiello, Dennis A. Ausiello, and Dale J. Benos.
Department of Physiology and Biophysics, University of Alabama at
Birmingham, Birmingham, Alabama 35294-0005 and Renal Unit -
Massachusetts General Hospital, East, Charlestown, MA 02129
APStracts 3:0372C, 1996.
Cystic Fibrosis (CF) airway epithelia exhibit enhanced Na&
reabsorption in parallel with diminished chloride secretion. We
tested the hypothesis that actin plays a role in the regulation of a
cloned epithelial Na& channel (ENaC) by the cystic fibrosis
transmembrane conductance regulator (CFTR). We found that
immunopurified bovine tracheal CFTR co-reconstituted into a planar
lipid bilayer with [alpha],[beta],[delta]-rENaC decreased single
channel open probability (Po) of rENaC in the presence of actin by
over 60%, a significantly greater effect than was observed in the
absence of actin (20%). In the presence of actin, PKA&ATP
activated both CFTR and rENaC, but CFTR was activated in a sustained
manner while the activation of rENaC was transitory. ATP alone could
also activate ENaC transiently in the presence of actin, but had no
effect on CFTR. Stabilizing short-actin filaments at a fixed length
with gelsolin (at 2:1 to actin ratio) produced a sustained activation
of [alpha],[beta],[delta]-rENaC in both the presence or absence of
CFTR. Gelsolin alone (i.e., in the absence of actin) had no effect on
the conductance or Po of either CFTR or rENaC. We have also found
that short actin filaments produced their modulatory action on
[alpha]-rENaC independent of the presence of the [beta]-, or [delta]-
rENaC subunits. In contrast, CFTR did not affect any properties of
the channel formed by [alpha]-rENaC alone, i.e., in the absence of
[beta]-, or [delta]-rENaC. These results indicate that CFTR can
directly downregulate single Na& channel activity, which may
account for the observed differences between Na& transport in
normal and CF affected airway epithelia. Moreover, the presence of
actin confers an enhanced modulatory ability of CFTR on Na&
channels.
Received 13 August 1996; accepted in final form 10 October 1996.
APS Manuscript Number C462-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996