Cyclic amp and swelling activated chloride conductance in rat
hepatocytes.
Meng, Xue-Jun, and Steven A. Weinman.
Departments of Internal Medicine and Physiology and Biophysics,
University of Texas Medical Branch, Galveston, Texas 77555-0641
APStracts 3:0026C, 1996.
An outwardly-rectifying chloride conductance was identified in primary
isolated rat hepatocytes and the whole-cell patch clamp technique was
used to characterize its properties and mechanisms of activation.
With symmetrical chloride-containing solutions on both sides and cAMP
(100 [mu]M) in the pipet solution, a large outwardly rectifying
conductance (1014 +/- 153 pS/pF, n=20) developed in all cells within
3 min. This cAMP-activated conductance was highly anion selective and
slowly inactivated at voltages greater than +80 mV. It was completely
inhibited by the anion channel blocker 5-nitro-2-(3
-phenylpropylamino)-benzoic acid (NPPB, 200 [mu]M, n=6) and partially
inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid
(DIDS, 150 [mu]M, n=7). It displayed a halide selectivity of I
->Br->Cl-. In the absence of cAMP, a functionally similar
conductance was activated by cell swelling. Reduction of bath
osmolality from 300 to 250 mosmol/kg increased membrane conductance
from 64 +/- 16.4 pS/pF to 487 +/- 23 pS/pF (n=4). This swelling
-activated conductance was also highly anion-selective and had
identical halide selectivity and blocker sensitivity as the cAMP
-activated conductance. Although cell swelling was not necessary for
cAMP-activation, cell shrinkage with hyperosmotic bath (350
mosmol/kg), either before or after exposure to cAMP, inhibited the
cAMP-activated conductance. By determining conductance as a function
of bath osmolality both in the presence and absence of cAMP, it was
observed that cAMP shifted the osmotic set-point for conductance
activation without changing either the maximum or minimum
conductance. In conclusion, both cAMP and cell swelling activate a
large outwardly-rectifying chloride conductance in rat hepatocytes.
Its ionic selectivity and sensitivity to channel blockers is
identical to that seen for swelling-activated chloride conductances
in many cell types. The conductive properties are not those of CFTR
-mediated chloride conductance. Cyclic AMP appears to activate this
conductance by altering the volume set-point of a swelling activated
channel.
Received 12 July 1995; accepted in final form 29 December 1995.
APS Manuscript Number C420-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 January 96