Angiotensin II receptor-mediated calcium influx in bovine adrenal glomerulosa cells.
The cytoplasmic calcium ([Ca2+]i) response to angiotensin II (AII) in bovine adrenal glomerulosa cells is characterized by an initial transient peak due to intracellular Ca2+ mobilization, followed by a sustained plateau phase that is dependent on Ca2+ entry from the extracellular fluid. In Fura-2 loaded cells, the calcium channel antagonists, nifedipine (1 microM) and verapamil (20 microM), only partially reduced the cytosolic calcium profile induced by AII. The dihydropyridine agonist, Bay K 8644, caused a moderate increase in [Ca2+]i when added in concentrations of 50-100 nM, but did not enhance the AII-induced rise in [Ca2+]i. These results indicate that most of the AII-stimulated Ca2+ influx is through channels that are insensitive to dihydropyridines and verapamil. In contrast, the inorganic Ca2+ channel blocker, LaCl3 (10 microM), inhibited the AII-induced plateau phase by more than 50%. The AII-induced Ca2+ signal was not affected by treatment with pertussis toxin (100-300 ng/ml for 12 h). The prior addition of specific AII-antagonists (DuP 753, a nonpeptide antagonist, and three peptide analogs, [Sar1,Thr8]AII, [Sar1,Ala8]AII, and [Sar1,Ile8]AII) completely inhibited the AII-induced Ca2+ signal. However, addition of up to 25,000 molar excess of these antagonists at intervals from 10 sec to 5 min after AII caused progressively less attenuation of the sustained Ca2+ signal. After 5 min, addition of antagonists did not inhibit the agonist-induced Ca2+ response for up to 20 min. The progressive loss of ability of the antagonists to inhibit the sustained elevation of [Ca2+]i could reflect prolonged activation of the receptor or of a subsequent process that maintains Ca2+ influx despite receptor blockade. It is possible that sequestration and/or endocytosis of the AII-receptor complex is accompanied by continued generation of intracellular signals that contribute to the maintenance of the [Ca2+]i response.
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Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Catt
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KJ
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000804:Angiotensin II / Q000037:antagonists & inhibitors; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D002417:Cattle; D002478:Cells, Cultured; D004095:Dihydropyridines / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology; D007093:Imidazoles / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D019808:Losartan; D037342:Pertussis Toxin; D011945:Receptors, Angiotensin / Q000502:physiology*; D013777:Tetrazoles / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D015384:Zona Glomerulosa / Q000378:metabolism*
D057911:Angiotensin Receptor Antagonists; D001713:Biphenyl Compounds; D015220:Calcium Channels; D004095:Dihydropyridines; D007093:Imidazoles; D011945:Receptors, Angiotensin; D013777:Tetrazoles; D010566:Virulence Factors, Bordetella; C028521:lanthanum chloride; D000804:Angiotensin II; D007811:Lanthanum; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D019808:Losartan; D002118:Calcium