Ionomycin enhances Ca2+ influx by stimulating store-regulated cation entry and not by a direct action at the plasma membrane.

TitleIonomycin enhances Ca2+ influx by stimulating store-regulated cation entry and not by a direct action at the plasma membrane.
Publication TypeJournal Article
Year of Publication1994
AuthorsMorgan, AJ, Jacob, R
JournalBiochem J
Volume300 ( Pt 3)
Pagination665-72
Date Published1994 Jun 15
ISSN0264-6021
KeywordsBiological Transport, Calcium, Calcium-Transporting ATPases, Cell Compartmentation, Cell Line, Cell Membrane, Cytoplasm, Endoplasmic Reticulum, Endothelium, Vascular, Histamine, Humans, Imidazoles, Indoles, Ionomycin, Manganese, Pyrilamine
Abstract

In fura-2-loaded ECV304 cells ionomycin elicited a saturable biphasic change in intracellular Ca2+ concentration ([Ca2+]i), where the initial phase represented mobilization of intracellular stores and the sustained component represented Ca2+ influx. To examine whether ionomycin could stimulate influx via a store-dependent mechanism. Mn2+ entry was monitored by the quenching of fura-2 fluorescence: influx was enhanced even after ionomycin wash-out, provided that internal stores were not refilled with Ca2+. Moreover, the maximal rate of histamine-stimulated Mn2+ entry was unaffected by ionomycin, suggesting a common route of entry. The Ca(2+)-entry blocker SK&F 96365 inhibited both the ionomycin-induced Mn2+ entry and the sustained [Ca2+]i response to the ionophore (leaving the initial peak [Ca2+]i response unaffected). In other experiments, although addition of ionomycin further increased the plateau phase induced by 100 microM histamine, the increase was completely abolished by pretreatment with the store Ca(2+)-ATPase inhibitor cyclopiazonic acid (CPA). Furthermore, in store-depleted cells, re-addition of 1 mM extracellular Ca2+ (in the presence of CPA plus histamine) led to a rapid rise in [Ca2+]i, dependent on Ca2+ influx, with kinetics that were not enhanced by ionomycin. These data suggest that ionomycin acts primarily at the level of the internal Ca2+ stores, so that, at the concentrations used here (

DOI10.1042/bj3000665
Alternate JournalBiochem. J.
Citation Key10.1042/bj3000665
PubMed ID8010948
PubMed Central IDPMC1138219
Grant List / / Wellcome Trust / United Kingdom