title: Regulation of Ca2+ channel currents by intracellular ATP in smooth muscle cells of rat mesenteric artery.
abstract: 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.
authors.affiliation: Department of Molecular and Cellular Physiology, College of Medicine, University of Cincinnati, Ohio 45267, USA.
authors.forename: H
authors.initials: H
authors.lastname: Yokoshiki
authors.forename: Y
authors.initials: Y
authors.lastname: Katsube
authors.forename: N
authors.initials: N
authors.lastname: Sperelakis
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D001464:Barium / Q000502:physiology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology; D004553:Electric Conductivity; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D008638:Mesenteric Arteries / Q000166:cytology / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D047428:Protein Kinase Inhibitors; D051381:Rats
chemical_list: D015220:Calcium Channels; D004791:Enzyme Inhibitors; D047428:Protein Kinase Inhibitors; D005576:Colforsin; D001464:Barium; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000255:Adenosine Triphosphate