title: Cytosolic free calcium regulation in response to acute changes in intracellular pH in vascular smooth muscle.
abstract: This study examined the mechanisms whereby alterations of intracellular pH (pHi) impact on free cytosolic calcium (Cai2+) in cultured rat aortic vascular smooth muscle cells (VSMC) assayed in the presence of HCO3/CO2. Rapid cell alkalinization, effected by the exposure to NH4Cl or removal of CO2 from the superfusate, produced a rapid increase in Cai2+. The rise in Cai2+ was markedly diminished when sarcoplasmic reticulum (SR) Ca2+ stores had been depleted by prior exposure to arginine vasopressin (AVP) in Ca(2+)-free media or when SR release and reuptake of Ca2+ were blocked by the addition of 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8), but was unaffected by the removal of external Ca2+ or inhibition of Ca2+ entry using NiCl2. Cell acidification also resulted in a rapid increase in Cai2+. This Cai2+ increase was most apparent when pHi was very low (< 6.6) and was unaffected by removal of external Ca2+ or NiCl2 addition. Unlike the effect of cell alkalinization, the increase in Cai2+ associated with cell acidification was not prevented by pretreatment with AVP or TMB-8. We conclude that, in cultured VSMC, acute intracellular alkalinization and, to a lesser extent, acidification result in release of Ca2+ from internal stores. Alkalinization increases Cai2+ by promoting its release from a store which is AVP and TMB-8 sensitive, most likely the SR. Cell acidification increases Cai2+ from an intracellular store(s) that is neither AVP nor TMB-8 sensitive. The increase in Cai2+ produced by cell acidification may be explained on the basis of cell buffering such that, as cytosolic H+ increases, it displaces Cai2+ from internal buffers with similar affinities for Ca2+ and H+.
authors: Department of Medicine, Northwestern University Medical School, Chicago, Illinois.
authors: D C
authors: DC
authors: Batlle
authors: R
authors: R
authors: Peces
authors: M S
authors: MS
authors: LaPointe
authors: M
authors: M
authors: Ye
authors: J T
authors: JT
authors: Daugirdas
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism*; D001127:Arginine Vasopressin / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002245:Carbon Dioxide / Q000494:pharmacology; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007424:Intracellular Fluid / Q000378:metabolism; D007700:Kinetics; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009532:Nickel / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000037:antagonists & inhibitors; D013997:Time Factors
chemical_list: D000643:Ammonium Chloride; D001127:Arginine Vasopressin; D002245:Carbon Dioxide; D004533:Egtazic Acid; C022838:nickel chloride; D009532:Nickel; D012964:Sodium; D002118:Calcium