Modulation of cytosolic Ca2+ concentration by thapsigargin and cyclopiazonic acid in human aortic endothelial cells.
To clarify the agonist-induced Ca2+ entry mechanism, effects of thapsigargin and cyclopiazonic acid, selective inhibitors of endoplasmic reticulum Ca(2+)-ATPase, on intracellular free Ca2+ concentration ([Ca2+]i) were studied in cultured human aortic endothelial cells loaded with the fluorescent Ca2+ indicator fura-2. Thapsigargin (1-1000 nM) and cyclopiazonic acid (0.1-100 microM) produced a biphasic change in [Ca2+]i, which consisted of a transient peak elevation followed by a long-lasting decline of [Ca2+]i in a concentration-dependent manner. In the presence of thapsigargin or cyclopiazonic acid, the rapid transient elevation of [Ca2+]i elicited by histamine was attenuated in a time-dependent manner. The slow declining phase of the response to thapsigargin and cyclopiazonic acid was completely eliminated by removal of extracellular Ca2+, and it was also prevented by reduction of the extracellular Cl- concentration to 40 mM or by the Cl- channel blocker N-phenylanthranilic acid. These findings suggest that the initial transient rising phase and the slow declining phase of [Ca2+]i in response to thapsigargin and cyclopiazonic acid reflect a blockade of Ca2+ uptake into the endoplasmic reticulum and the Cl(-)-sensitive Ca2+ entry activated by the depletion of agonist-sensitive intracellular Ca2+ stores, respectively, in human aortic endothelial cells.
Hosoki
E
E
Department of Pharmacology, Akita University School of Medicine, Japan.
Iijima
T
T
D001011:Aorta / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002478:Cells, Cultured; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D018118:Chloride Channels; D002712:Chlorides; D007211:Indoles; D013729:Terpenes; D019284:Thapsigargin; D006632:Histamine; D000252:Calcium-Transporting ATPases; D002118:Calcium; C000543:cyclopiazonic acid