Regulation of ca2+ channel currents by intracellular atp in smooth
muscle cells of rat mesenteric artery.
Yokoshiki, Hisashi, Yasuhiro Katsube, Nicholas Sperelakis.
Department of Molecular and Cellular Physiology, College of
Medicine, University of Cincinnati, Cincinnati, Ohio 45267, USA
APStracts 3:0392H, 1996.
Regulation of L-type Ca2+ channels (ICa(L)) of vascular smooth muscle
(VSM) cells by cAMP-dependent and cGMP-dependent phosphorylation,
which requires Mg2+ATP as a phosphate donor, has been reported (5,
17, 23, 25, 26), and regulation by ATP has been demonstrated (10,
11). However, it has not been elucidated whether the regulation by
ATP ismediated by a mechanism that is distinct from phosphorylation.
In the present study, we examined the effects of intracellularly
-perfused ATP on Ca2+ channel currents of VSM cells isolated from rat
mesenteric arteries using whole-cell voltage clamp combined with an
intracellular perfusion technique. Ba2+ currents (IBa) through Ca2+
channels were evoked by depolarizing pulses from a holding potential
of -80 mV with 130 mM Cs+ in the pipette and 100 mM Ba2+ in the bath.
Decrease in the ATP concentration (from 5 to 0.1 mM) in the pipette
caused 45 +/- 5 % (n = 8) reduction of maximal IBa obtained at +40 mV
within 10 min. The dose-response relation between IBa and ATP showed
a dissociation constant of 0.53 mM ATP. This concentration is much
higher than that usually required for phosphorylation (e.g., few
micromolar (3)). Increase in the ATP (from 0.1 to 5 mM) caused an
enhancement of maximal IBa by 57 +/- 10 % (n = 6), and this
enhancement was not prevented in the presence of 30 [mu]M H-7, a non
-specific inhibitor of protein kinases, or 1 [mu]M PKI, an inhibitor
protein of cAMP-dependent protein kinase. These results indicate that
slow Ca2+ channels in VSM cells are regulated by intracellular ATP
independent of phosphorylation, implying a direct regulatory action,
such as a requirement for ATP binding to the inner surface of the
channel in order for it to exhibit activity.
Received 26 January 1996; accepted in final form 29 August 1996.
APS Manuscript Number H78-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996