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Biophys J, July 2000, p. 298-313, Vol. 79, No. 1
and
*Departments of Physiology and Pediatrics, Center for Cell and
Molecular Signaling, Emory University School of Medicine, Atlanta,
Georgia 30322, and
Division of Biology, California
Institute of Technology, Pasadena, California 91125 USA
The cystic fibrosis transmembrane conductance regulator
(CFTR) is a chloride channel with distinctive kinetics. At the
whole-cell level, CFTR currents in response to voltage steps are time
independent for wild type and for the many mutants reported so far.
Single channels open for periods lasting up to tens of seconds; the
openings are interrupted by brief closures at hyperpolarized, but not
depolarized, potentials. Here we report a serine-to-phenylalanine
mutation (S1118F) in the 11th transmembrane domain that confers
voltage-dependent, single-exponential current relaxations and moderate
inward rectification of the macroscopic currents upon expression in
Xenopus oocytes. At steady state, the S1118F-CFTR
single-channel conductance rectifies, corresponding to the whole-cell
rectification. In addition, the open-channel burst duration is
decreased 10-fold compared with wild-type channels. S1118F-CFTR
currents are blocked in a voltage-dependent manner by
diphenylamine-2-carboxylate (DPC); the affinity of S1118F-CFTR for DPC
is similar to that of the wild-type channel, but blockade exhibits
moderately reduced voltage dependence. Selectivity of the channel to a
range of anions is also affected by this mutation. Furthermore, the
permeation properties change during the relaxations, which suggests
that there is an interaction between gating and permeation in this
mutant. The existence of a mutation that confers voltage dependence
upon CFTR currents and that changes kinetics and permeation properties
of the channel suggests a functional role for the 11th transmembrane
domain in the pore in the wild-type channel.
Biophys J, July 2000, p. 298-313, Vol. 79, No. 1
© 2000 by the Biophysical Society 0006-3495/00/07/298/16 $2.00
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