AJP - Heart and Circulatory Physiology, Vol 272, Issue 2 814-H819, Copyright © 1997 by American Physiological Society

ARTICLES

Regulation of Ca2+ channel currents by intracellular ATP in smooth muscle cells of rat mesenteric artery

H. Yokoshiki, Y. Katsube and N. Sperelakis
Department of Molecular and Cellular Physiology, College of Medicine, University of Cincinnati, Ohio 45267, USA.

Regulation of L-type Ca2+ channels of vascular smooth muscle (VSM) cells by adenosine 3',5'-cyclic monophosphate (cAMP)-dependent and guanosine 3',5'-cyclic monophosphate (cGMP)-dependent phosphorylation, which requires Mg2+ATP as a phosphate donor, has been reported (T. Ishikawa, J. R. Hume, and K. D. Keef. Circ. Res. 73: 1128-1137, 1993; Z. Xiong, N. Sperelakis, and C. Fenoglio-Preiser. J. Vasc. Res. 31: 271-279, 1994), and regulation by ATP has been demonstrated (Y. Ohya and N. Sperelakis. Circ. Res. 64: 145-154, 1989). However, it has not been elucidated whether the regulation by ATP is mediated 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 a whole cell voltage clamp combined with an intracellular perfusion technique. Ba2+ currents (I(Ba)) 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. The decrease in the ATP concentration (from 5 to 0.1 mM) in the pipette caused a 45 +/- 5% (n = 8) reduction of maximal I(Ba) obtained at +40 mV within 10 min. The dose-response relation between I(Ba) 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). Increase in the ATP (from 0.1 to 5 mM) caused an enhancement of maximal I(Ba) by 57 +/- 10% (n = 6), and this enhancement was not prevented in the presence of 30 microM H-7, a nonspecific inhibitor of protein kinases, or 1 microM protein kinase inhibitor, an inhibitor protein of cAMP-dependent protein kinase. These results indicate that slow Ca2+ channels in VSM cells are regulated by intracellular ATP, independently of phosphorylation, implying a direct regulatory action, such as a requirement for ATP binding to the inner surface of the channel, to exhibit activity.

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