Regulation of the atrial muscarinic k+ channel activity by a
cytosolic protein via g protein-independent pathways.
Hong, Seong-Geun, Apisate Pleumsamran, and Donghee Kim.
Department of Physiology and Biophysics, Chicago Medical School,
3333 Green Bay Road, North Chicago, IL 60064.
APStracts 2:0374H, 1995.
Rapid desensitization of the muscarinic K+ current (KACh current) is
observed in cell-attached patches with 10 mM ACh in the pipette. When
inside-out patches were formed within 1 s after formation of cell
-attached patches, and GTP applied to the cytoplasmic side of the
membrane, desensitization was not observed, indicating that a
cytosolic factor mediated the desensitization. Applying the atrial
cytosolic extract directly to the cytoplasmic side of such inside-out
patches elicited a rapid desensitization of the KACh current. ATP (1
-4 mM) reversed this effect of the cytosol and reverted the KACh
channel to the undesensitized state. These effects of ATP and cytosol
on the KACh channel could occur in the absence of GTP or in the
presence of 100 mM GTPgS, indicating that G protein was not involved.
Treatment of the cytosol with proteases (trypsin, chymotrypsin,
bacterial protease) or heat-denaturation abolished the effect of the
cytosol on the KACh channel kinetics, indicating that the cytosolic
factor was a protein. Functional assay of the fractions collected
from gel filtration column indicated that the molecular weight of the
native protein was 95-130 kdaltons. We conclude that a large
cytosolic protein mediates the rapid desensitization of the KACh
channel current via a G protein-independent pathway.
Received 17 January 1995; accepted in final form 21 July 1995.
APS Manuscript Number H36-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 15 September 1995.