Dissociation of Ca2+ entry and Ca2+ mobilization responses to angiotensin II in bovine adrenal chromaffin cells.
In fura-2-loaded bovine adrenal chromaffin cells, 0.5 microM angiotensin II (AII) stimulated a 185 +/- 19 nM increase of intracellular-free calcium [( Ca2+]i) approximately 3 s after addition. The time from the onset of the response until achieving 50% recovery (t 1/2) was 67 +/- 10 s. Concomitantly, AII stimulated both the release of 45Ca2+ from prelabeled cells, and a 4-5-fold increase of [3H]inositol 1,4,5-trisphosphate [( 3H]Ins(1,4,5)P3) levels. In the presence of 50 microM LaCl3, or when extracellular-free Ca2+ [( Ca2+]o) was less than 100 nM, AII still rapidly increased [Ca2+]i by 95-135 nM, but the t 1/2 for recovery was then only 23-27 s. In medium with 1 mM MnCl2 present, AII also stimulated a small amount of Mn2+ influx, as judged by quenching of the fura-2 signal. When [Ca2+]o was normal (1.1 mM) or low (less than 60 nM), 1-2 microM ionomycin caused [Ca2+]i to increase 204 +/- 26 nM, while also releasing 45-55% of bound 45Ca2+. With low [Ca2+]o, ionomycin pretreatment abolished both the [Ca2+]i increase and 45Ca2+ release stimulated by AII. However, after ionomycin pretreatment in normal medium, AII produced a La3+-inhibitable increase of [Ca2+]i (103 +/- 13 nM) with a t 1/2 of 89 +/- 8 s, but no 45Ca2+ release. No pretreatment condition altered AII-induced formation of [3H]Ins(1,4,5)P3. We conclude that AII increased [Ca2+]i via rapid and transient Ca2+ mobilization from Ins(1,4,5)P3- and ionomycin-sensitive stores, accompanied (and/or followed) by Ca2+ entry through a La3+-inhibitable divalent cation pathway. Furthermore, the ability of AII to activate Ca2+ entry in the absence of Ca2+ mobilization (i.e. after ionomycin pretreatment) suggests a receptor-linked stimulus other than Ca2+ mobilization initiates Ca2+ entry.
Stauderman
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Merrell Dow Research Institute, Cincinnati, Ohio 45215.
Pruss
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D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism*; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002413:Cations, Divalent; D002417:Cattle; D002712:Chlorides; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007424:Intracellular Fluid / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology; D017895:Manganese Compounds; D013050:Spectrometry, Fluorescence
D002132:Calcium Radioisotopes; D002413:Cations, Divalent; D002712:Chlorides; D017895:Manganese Compounds; C028521:lanthanum chloride; D000804:Angiotensin II; D008345:Manganese; D004533:Egtazic Acid; D015759:Ionomycin; D007811:Lanthanum; D015544:Inositol 1,4,5-Trisphosphate; C025340:manganese chloride; D002118:Calcium