title: Histamine-induced Ca2+ entry precedes Ca2+ mobilization in bovine adrenal chromaffin cells.
abstract: The relationship between histamine-induced Ca2+ mobilization and Ca2+ entry in bovine adrenal chromaffin cells has been investigated. Stopped-flow fluorimetry of fura-2-loaded chromaffin cell populations revealed that 10 microM histamine promoted entry of Ca2+ or Mn2+ without measurable delay (< or = 20 ms), through a pathway that was insensitive to the dihydropyridine antagonist nifedipine. In the absence of extracellular Ca2+, or in the presence of 100 microM La3+, a blocker of receptor-mediated Ca2+ entry, 10 microM histamine triggered an elevation in intracellular calcium concentration ([Ca2+]i), but only after a delay of approx. 200 ms, which presumably represented the time required to mobilize intracellular Ca2+. These data suggested that histamine-induced bivalent-cation entry precedes extensive Ca2+ mobilization in chromaffin cells. In order to confirm that histamine can promote Ca2+ entry largely independently of mobilizing intracellular Ca2+, the ability of histamine to promote Ca2+ entry into cells whose intracellular Ca2+ store had been largely depleted was assessed. Fura-2-loaded chromaffin cells were treated with 10 microM ryanodine together with 40 mM caffeine, to deplete the hormone-sensitive Ca2+ store. This resulted in an approx. 95% inhibition of histamine-induced Ca2+ release. Under these conditions, histamine was still able to promote an entry of Ca2+ that was essentially indistinguishable from that promoted in control cells. In single cells, introduction of heparin (100 mg/ml), but not de-N-sulphated heparin (100 mg/ml), abolished the histamine-induced rise in [Ca2+]i. All these data suggest that histamine can induce G-protein- or inositol phosphate-dependent rapid (< or = 20 ms) Ca2+ entry without an extensive intracellular mobilization response in chromaffin cells, which points to activation of an entry mechanism distinct from the Ca(2+)-release-activated Ca2+ channel found in non-excitable cells.
authors.affiliation: AFRC Laboratory of Molecular Signalling, Department of Zoology, Cambridge, U.K.
authors.forename: T R
authors.initials: TR
authors.lastname: Cheek
authors.forename: M M
authors.initials: MM
authors.lastname: Murawsky
authors.forename: K A
authors.initials: KA
authors.lastname: Stauderman
mesh_terms: D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent; D002417:Cattle; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D016257:Fura-2; D019204:GTP-Binding Proteins / Q000502:physiology; D006632:Histamine / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000494:pharmacology; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D008345:Manganese / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D013050:Spectrometry, Fluorescence
chemical_list: D002413:Cations, Divalent; D007295:Inositol Phosphates; D008345:Manganese; D004533:Egtazic Acid; D007811:Lanthanum; D006632:Histamine; D019204:GTP-Binding Proteins; D011188:Potassium; D002118:Calcium; D016257:Fura-2