title: Inositol trisphosphate-dependent and -independent Ca2+ mobilization pathways at the vacuolar membrane of Candida albicans.
abstract: Vacuolar membrane vesicles were isolated from Candida albicans protoplasts, and marker enzyme assays were employed to identify the membranes as vacuolar in origin. The mechanisms of Ca2+ uptake and Ca2+ release at the vacuolar membrane were investigated. Ca2+ accumulation by vacuolar membrane vesicles can be generated via H+/Ca2+ antiport. The inside-acid pH is in turn generated by a vacuolar-type H(+)-ATPase, as demonstrated by the sensitivity of Ca2+ uptake to ionophores and the vacuolar H(+)-ATPase inhibitor bafilomycin A1. Vacuolar membrane vesicles exhibit two Ca2+ release pathways: one induced by inositol 1,4,5-trisphosphate (InsP3) and the other by inside-positive voltage. These two pathways are distinct with respect to the amount of Ca2+ released, the nature of response to successive stimuli, and their respective pharmacological profiles. The InsP3-gated pathway exhibits a K0.5 for InsP3 of 2.4 microM but is not activated by inositol 4,5-bisphosphate or inositol 1,3,4,5-tetrakisphosphate at concentrations up to 50 microM. Ca2+ release by InsP3 is blocked partially by low molecular weight heparin. Ca2+ released by the voltage-sensitive pathway occurs at membrane potentials estimated to be over a physiological range from 0 to 80 mV. The voltage-sensitive Ca2+ release pathway can be blocked by lanthanide ions and organic channel blockers such as ruthenium red and verapamil. Furthermore, the voltage-sensitive Ca2+ release pathway exhibits Ca(2+)-induced Ca2+ release. These findings are discussed in relation to the mechanism of Ca(2+)-mediated cellular signaling in C. albicans and other fungi.
authors.affiliation: Biology Department, University of York, United Kingdom.
authors.forename: C M
authors.initials: CM
authors.lastname: Calvert
authors.forename: D
authors.initials: D
authors.lastname: Sanders
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002176:Candida albicans / Q000378:metabolism*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000494:pharmacology; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D018942:Macrolides; D008345:Manganese / Q000494:pharmacology; D009861:Onium Compounds / Q000494:pharmacology; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D013104:Spheroplasts / Q000378:metabolism; D014320:Triphenylmethyl Compounds / Q000494:pharmacology; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D007295:Inositol Phosphates; D018942:Macrolides; D009861:Onium Compounds; D014320:Triphenylmethyl Compounds; C011561:triphenylmethylphosphonium; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D008345:Manganese; D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; C040929:bafilomycin A1; D006493:Heparin; D014700:Verapamil; D006180:Proton-Translocating ATPases; D002118:Calcium