AJP - Cell Physiology, Vol 258, Issue 2 C352-C368, Copyright © 1990 by American Physiological Society
Chloride channels in the apical membrane of a distal nephron A6 cell line
Y. Marunaka and D. C. Eaton
Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322.
In this report, single-channel recording methods were used to determine
whether there are Cl- conductive pathways in the apical membrane of
cultured renal distal nephron cells (A6). Two different types of single Cl-
channels were observed. In cell-attached patches, one had a unit
conductance of 3 pS, whereas the unit conductance of the other was 8 pS. In
cell-attached patches, the currents associated with the 3-pS Cl- channel
outwardly rectified, whereas the current voltage relationship for the 8-pS
Cl-channel was linear. The 3-pS Cl- channel has one open and one closed
state; the 8-pS Cl- channel has one open and two closed states. The open
probability of the 3-pS Cl- channel was voltage dependent (increasing with
depolarization of the membrane) but even at very depolarized potentials
(+140 mV) remained small (always less than 0.1). On the other hand, the
open probability of the 8-pS Cl- channel was large (approximately 0.8) and
voltage independent. The closing rate of the 3-pS Cl- channel was decreased
when the patch membrane was depolarized, whereas the opening rate was
increased. In contrast, the closing rate of the 8-pS Cl- channel decreased
with depolarization, but the opening rates were voltage independent. The
outward rectification of the 3-pS channel was markedly reduced in
inside-out patches when high calcium concentrations (10-800 microM) were
present on the intracellular surface. The open probability of the 3-pS Cl-
channel is increased by membrane permeable analogues of adenosine
3',5'-cyclic monophosphate primarily by decreasing the mean closed time.
