Multiple mechanisms of activating Ca2+ entry in freshly isolated rabbit aortic endothelial cells.
In Fura-2-loaded, freshly isolated rabbit aortic endothelial cells the Ca2+ entry pathway was investigated using the Mn2(+)-quenching technique. Acetylcholine (ACh) interaction with muscarinic receptors activated Mn2+ influx through the plasma membrane. Sarcoplasmic-endoplasmic reticulum Ca2+ ATPase blockers such as cyclopiazonic acid (CPA), thapsigargin and BHQ, which block the endoplasmic reticulum Ca2+ pump and do not interact with receptors, also activated Mn2+ influx. Mn2+ influx activated by either ACh or CPA was blocked by the following agents: SKF96365, a receptor-operated Ca2+ channel (ROC) blocker; NCDC, a PLC and ROC blocker, and genistein, a tyrosine kinase inhibitor. D600, the L-type Ca2+ channel blocker, had no significant effect on Mn2+ influx. Caffeine blocked the ACh-induced Ca2+ release but had no effect on the ACh-induced Mn2+ influx. Similarly dantrolene, which blocked intracellular Ca2+ release induced by ACh, did not affect the ACh-activated Mn2+ influx. These data suggest that ACh can activate Ca2+ influx without depletion of the ACh-sensitive intracellular Ca2+ store. It is concluded (1) that in freshly isolated endothelial cells depletion of the intracellular Ca2+ store is not necessary for ACh-activated Ca2+ influx, and (2) that receptor activation and intracellular Ca2+ store depletion may activate the same Ca2+ entry pathway through parallel mechanisms.
Wang
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Department of Pharmacology and Therapeutics, The University of British Columbia, Vancouver, Canada.
van Breemen
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D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002469:Cell Separation; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D007211:Indoles; D008345:Manganese; D000252:Calcium-Transporting ATPases; D000109:Acetylcholine; D002118:Calcium; C000543:cyclopiazonic acid