Flickery block of single cftr chloride channels by intracellular
anions and osmolytes.
Linsdell, Paul, and John W. Hanrahan.
Department of Physiology, McGill University, 3655 Drummond St.,
Montreal, Quebec, H3G 1Y6, Canada
APStracts 3:0080C, 1996.
Cystic fibrosis transmembrane conductance regulator (CFTR) is a
phosphorylation- and nucleotide-dependent chloride channel. Single
CFTR currents recorded on-cell show slight outward rectification,
which has previously been suggested to be due to an asymmetrical
chloride ion gradient or to a specific interaction between permeant
intracellular anions and the channel. Using single channel recording
from Chinese hamster ovary cells stably expressing CFTR, we have
found that both the sparingly permeant anion glutamate and the
impermeant anion gluconate cause a rapid, voltage-dependent block of
CFTR channels when applied to the intracellular, but not the
extracellular face of excised patches. Both the affinity and the
voltage dependence of block were affected by the extracellular
chloride concentration in a manner consistent with chloride ions
being able to repel these blocking ions from the pore. These results
are discussed in terms of previous models of CFTR current outward
rectification, and it is suggested that this rectification may result
from a combination of asymmetrical chloride concentrations and
voltage-dependent block of the channel by large cytoplasmic anions.
In addition, we find that CFTR conductance is decreased by high
concentrations of intracellular sucrose, sorbitol and urea in a
manner consistent with a rapid block of the channel by these
molecules.
Received 9 November 1995; accepted in final form 16 February
1996.
APS Manuscript Number C679-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96