Regulation of whole cell currents by cytosolic camp, ca2+ and cl-
in rat fetal distal lung epithelium.
Nakahari, Takashi, and Yoshinori Marunaka.
The Medical Research Council Group in Lung Development and Division
of Respiratory Research, The Hospital for Sick Children Research
Institute and The University of Toronto Faculty of Medicine, Toronto,
Ontario, Canada M5G 1X8
APStracts 2:0122C, 1995.
The whole-cell patch clamp technique was used to study ionic
conductances in fetal distal lung epithelial (FDLE) cells. In
unstimulated FDLE cells, K+ conductances were detected in lowered
intracellular Cl- concentration ([Cl-]i, = 50 mM). The whole-cell
currents of FDLE cells were increased by elevation of intracellular
Ca2+ ([Ca2+]i), or cAMP concentration, ([cAMP]i). The elevation of
[Ca2+]i activated the K+ currents. The amiloride-blockable whole-cell
currents were activated by [cAMP]i of 1 mM with [Cl-]i of 20 mM and
were more frequently detected in the pipette solution without EGTA
than with it (0.5 mM). When the [Cl-]i was fixed at 50 or 145 mM,
however, the increase in these currents was not detected even with
cAMP and without EGTA. The amiloride-blockable currents were detected
in both the Na and K pipette solutions. Thus, the increase in
amiloride-blockable whole-cell currents was due to the activation of
nonselective cation channels. In FDLE cells treated with terbutaline
which is a [beta]2-adrenergic receptor agonist or forskolin, these
currents were detected in the pipette solution containing 20 mM Cl-,
but were suppressed with time when the pipette solution contained 50
or 145 mM Cl-. It seems likely that maintenance of [Cl-]i at the
lowered level is an important requirement for the FDLE cells to
activate the amiloride-blockable whole-cell currents. It is proposed
that cellular mechanisms, such as cell shrinkage, exist to reduce the
[Cl-]i in response to cAMP.
Received 8 August 1994; accepted in final form 13 January 1995.
APS Manuscript Number C475-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 March 1995.