title: Intracellular calcium buffering shapes calcium oscillations in Xenopus melanotropes.
abstract: The pituitary melanotrope cell of Xenopus laevis displays cytosolic Ca2+ oscillations that arise for the interplay between the burst-like openings of voltage-operated Ca2+ channels and Ca2+-extrusion mechanisms. We have previously shown that Ca2+-extrusion rates increase with increases in [Ca2+]i, suggesting that Ca2+ itself plays a role in shaping the Ca2+ oscillations. The purpose of the present study was to test this hypothesis by manipulating the intracellular Ca2+ buffering capacity of the cell and determining the consequences of such manipulations for the shape of the Ca2+ oscillations. We manipulated the cytosolic buffering capacity by loading the fast Ca2+ chelator BAPTA into cells. During loading the [Ca2+]i was dynamically imaged with confocal laser scanning microscopy. The basal [Ca2+]i was reduced with BAPTA loading and this reduction was associated with lower Ca2+-extrusion rates, a broadening of the Ca2+ oscillations and declined oscillation frequencies. Short loading periods of the buffer led to new, stable patterns of Ca2+ signaling and to reduced but stable levels of peptide secretion. We propose that the cytosolic Ca2+ buffer capacity, and thus by inference the profile of intracellular Ca2+ buffering proteins, is an important factor in setting the frequency and shape of Ca2+ oscillations.
authors.affiliation: Department of Cellular Animal Physiology, Institute of Cellular Signalling, University of Nijmegen, Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.
authors.forename: W J
authors.initials: WJ
authors.lastname: Koopman
authors.forename: W J
authors.initials: WJ
authors.lastname: Scheenen
authors.forename: L F
authors.initials: LF
authors.lastname: Schoolderman
authors.forename: P M
authors.initials: PM
authors.lastname: Cruijsen
authors.forename: E W
authors.initials: EW
authors.lastname: Roubos
authors.forename: B G
authors.initials: BG
authors.lastname: Jenks
mesh_terms: D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000008:administration & dosage / Q000494:pharmacology; D004533:Egtazic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D009991:Oscillometry; D010455:Peptides / Q000378:metabolism; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D013997:Time Factors; D014982:Xenopus laevis
chemical_list: D002021:Buffers; D002614:Chelating Agents; D010455:Peptides; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D009074:Melanocyte-Stimulating Hormones; D002118:Calcium