Modulation of calcium homeostasis in cultured rat aortic endothelial cells by intracellular acidification.
Acidosis produces vasodilation in a process that may involve the vascular endothelium. Because synthesis and release of endothelium-derived vasodilatory substances are linked to an increase in cytosolic calcium concentration ([Ca2+]i), we examined the effect of intracellular acidification on cultured rat aortic endothelial cells loaded either with the pH-sensitive probe carboxy-seminaphthorhodafluor-1 or the Ca(2+)-sensitive fluorescent probe indo 1. The basal cytosolic pH (pHi) of endothelial monolayers in a 5% CO2-HCO3- buffer was 7.27 +/- 0.02 and that in a bicarbonate-free solution was 7.22 +/- 0.03. Acidification was induced either by removal of NH4Cl (delta pHi = -0.10 +/- 0.02), changing from a bicarbonate-free to a 5% CO2-HCO3(-)-buffered solution at constant buffer pH (delta pHi = -0.18 +/- 0.03), or changing from a 5% to a 20% CO2-HCO3- solution (delta pHi = -0.27 +/- 0.07). Regardless of the method used, intracellular acidification increased [Ca2+]i as indexed by indo 1 fluorescence. The increase in [Ca2+]i induced by changing from a 5 to a 20% CO2-HCO3- solution was not significantly altered by removal of buffer Ca2+ either before or after depletion of bradykinin- and thapsigargin-sensitive intracellular Ca2+ stores. Thus intracellular acidification of vascular endothelial cells releases Ca2+ into the cytosol either from pH-sensitive intracellular buffer sites, mitochondria, or from bradykinin- and thapsigargin-insensitive intracellular stores. This Ca2+ mobilization may be linked to endothelial synthesis and release of vasodilatory substances during acidosis.
Ziegelstein
R C
RC
Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore 21224.
Cheng
L
L
Blank
P S
PS
Spurgeon
H A
HA
Lakatta
E G
EG
Hansford
R G
RG
Capogrossi
M C
MC
D000143:Acids / Q000378:metabolism*; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism*; D001639:Bicarbonates / Q000494:pharmacology; D001920:Bradykinin / Q000494:pharmacology; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002245:Carbon Dioxide / Q000494:pharmacology; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D000143:Acids; D001639:Bicarbonates; D002021:Buffers; D013729:Terpenes; D000643:Ammonium Chloride; D002245:Carbon Dioxide; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D001920:Bradykinin; D002118:Calcium