Different properties of the atrial g protein-gated k+ channels
activated by extracellular atp and adenosine.
Fu, Chen, Apisate Pleumsamran, Uhtaek Oh, and Donghee Kim.
Department of Physiology and Biophysics, The Chicago Medical
School, 3333 Green Bay Road, North Chicago, IL 60064
APStracts 2:0187H, 1995.
Extracellular ATP (ATPo) and adenosine activate G protein-gated,
inwardly rectifying K+ currents in atrial cells. Earlier studies have
suggested that the two agonists may use separate pathways to activate
the K+ current. Therefore, we examined whether the K+ channels
activated by the two agonists have different properties under
identical ionic conditions. In cell-attached patches, K+ channels
activated by 100 mM ATP in the pipette had a single-channel
conductance and mean open time of 32.0 0.2 pS and 0.5 0.1 ms,
respectively, compared with 31.3 0.3 pS and 0.9 0.1 ms for the K+
channels activated by adenosine (140 mM KCl). With ATPo as the
agonist, the K+ channel activity in cell-attached patches was 3 fold
lower than that in inside-out patches with 100 mM GTP in the bath.
Applying ATP to the cytoplasmic side of the membrane (ATPi) produced
a biphasic concentration-dependent effect on channel activity: an
increase at low (K1/2=190 mM) and a decrease at high (K1/2=1.3 mM)
concentrations. In contrast, with adenosine as the agonist, K+
channel activity in cell-attached patches was 4 fold greater than
that in inside-out patches with 100 mM GTP in the bath. In inside-out
patches, ATPi only augmented the K+ channel activity (K1/2=32 mM).
These results show that although both ATPo and adenosine activate
kinetically similar K+ channels in atrial cells, the channels are
regulated differently by intracellular nucleotides.
Received 11 October 1995; accepted in final form 24 April 1995.
APS Manuscript Number H904-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 9 May 1995.