Atp-dependent regulation of a g protein-coupled k+ channel (girk1/
girk4) expressed in oocytes.
Kim, Donghee, Marshall Watson, and Virginia Indyk.
Department of Physiology and Biophysics, Finch University of Health
Sciences/The Chicago Medical School, 3333 Green Bay Road, North
Chicago, IL 60064
APStracts 3:0283H, 1996.
Recent studies suggest that activation of the atrial muscarinic K+
current by acetylcholine (ACh) involves an ATP-dependent process
which is then inhibited by a cytosolic protein to result in the rapid
desensitization. To obtain further evidence in support of such a
dually-regulated process, we studied the properties of GIRK1 and
GIRK4 which, when co-expressed in oocytes, form a heteromultimer that
closely resembles the muscarinic K+ channel. Acetylcholine (ACh)
activated an inwardly rectifying K+ current which desensitized
slowly. In cell-attached patches with ACh in the pipette, the mean
open times (to) of GIRK1/GIRK4 were 1.2+/-0.1 (28%) and 6.7+/-0.8 ms
(72%), and did not change significantly with time. However, in
inside-out patches, the to of GIRK1/GIRK4 activated with GTP[gamma]S
was 1.3+/-0.1 ms (100%), and the channel activity (NPo) was 5 fold
lower. These changes in channel kinetics did not occur in the
presence of sodium orthovanadate (3 mM), an inhibitor of phosphatase.
Addition of 1 mM ATP, but not adenylimidodiphosphate (AMPPNP), to
inside-out patches resulted in increases in NPo (4.8 fold) and the
open time duration of GIRK1/GIRK4 such that to were 1.2+/-0.2 ms
(32%) and 6.2+/-0.6 ms (68%). Single-channel conductances were
unchanged (34+/-1 pS). Cytosolic extract from atria, but not oocytes,
could reverse these effects of ATP. These results provide further
evidence that the antagonistic modulation of G protein-gated K+
channels by ATP and the atrial cytosolic protein produces the early
rapid desensitization in atrial cells. In oocytes, the ATP-dependent
step is dominant, and thus provides a major component of the total
GIRK1/GIRK4 current activated by ACh.
Received 31 January 1996; accepted in final form 26 June 1996.
APS Manuscript Number H92-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996