Intracellular alkalinization induces Ca2+ influx via non-voltage-operated Ca2+ channels in rat aortic smooth muscle cells.
In smooth muscle, the cytosolic Ca2+ concentration ([Ca2+](i)) is the primary determinant of contraction, and the intracellular pH (pH(i)) modulates contractility. Using fura-2 and 2',7'-biscarboxyethyl-5(6) carboxyfluorescein (BCECF) fluorometry and rat aortic smooth muscle cells in primary culture, we investigated the effect of the increase in pH(i) on [Ca2+](i). The application of the NH(4)Cl induced concentration-dependent increases in both pH(i) and [Ca2+](i). The extent of [Ca2+](i) elevation induced by 20mM NH(4)Cl was approximately 50% of that obtained with 100mM K(+)-depolarization. The NH(4)Cl-induced elevation of [Ca2+](i) was completely abolished by the removal of extracellular Ca2+ or the addition of extracellular Ni2+. The 100mM K(+)-induced [Ca2+](i) elevation was markedly inhibited by a voltage-operated Ca2+ channel blocker, diltiazem, and partly inhibited by a non-voltage-operated Ca2+ channel blocker, SKF96365. On the other hand, the NH(4)Cl-induced [Ca2+](i) elevation was resistant to diltiazem, but was markedly inhibited by SKF96365. It is thus concluded that intracellular alkalinization activates the Ca2+ influx via non-voltage-operated Ca2+ channels and thereby increases [Ca2+](i) in the vascular smooth muscle cells. The alkalinization-induced Ca2+ influx may therefore contribute to the enhancement of contraction.
Division of Molecular Cardiology, Research Institute of Angiocardiology, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Wakako
W
Eto
Katsuya
K
Hirano
Mayumi
M
Hirano
Junji
J
Nishimura
Hideo
H
Kanaide
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000166:cytology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects*; D002478:Cells, Cultured; D004110:Diltiazem / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space / Q000378:metabolism; D005452:Fluoresceins; D005470:Fluorometry; D016257:Fura-2; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology; D007424:Intracellular Fluid / Q000187:drug effects; D008297:Male; D009119:Muscle Contraction; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005452:Fluoresceins; D007093:Imidazoles; D000643:Ammonium Chloride; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D004110:Diltiazem; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium; D016257:Fura-2