title: Calcium dynamics during physiological acidification in Xenopus oocyte.
abstract: Interplays between intracellular pH (pHi) and calcium ([Ca(2+)](i)) variations remain unclear, though both proton and calcium homeostasis changes accompany physiological events such as Xenopus laevis oocyte maturation. In this report, we used NH(4)Cl and changes of extracellular pH (pHe) to acidify the cytosol in a physiological range. In oocytes voltage-clamped at -80 mV, NH(4)Cl triggered an inward current, the main component of which is a Ca(2+)-dependent chloride current. Calcium imaging confirmed that NH(4)Cl provoked a [Ca(2+)](i) increase. The mobilized sources of calcium were discriminated using the triple-step protocol as a means to follow both the calcium-activated chloride currents (ICl-Ca) and the hyperpolarization- and acid-activated nonselective cation current (I(In)). These currents were stimulated during external addition of NH(4)Cl. This upregulation was abolished by BAPTA-AM, caffeine and heparin. By both buffering pHi changes with MOPS and by inhibiting calcium influx with lanthanum, intracellular acidification, initiated by NH(4)Cl and extracellular acidic medium, was shown to trigger a [Ca(2+)](i) increase through both calcium release and calcium influx. The calcium pathways triggered by pHe changes are similar to those activated by NH(4)Cl, thus suggesting that there is a robust signaling mechanism allowing the cell to adjust to variable environmental conditions.
authors: Laboratoire de Régulation des Signaux de Division, EA 4479, IFR 147, Université Lille 1, Villeneuve d'Ascq, France. matthieu.marin@univ-lille1.fr
authors: Matthieu
authors: M
authors: Marin
authors: Chantal
authors: C
authors: Sellier
authors: Anne Frédérique
authors: AF
authors: Paul-Antoine
authors: Katia
authors: K
authors: Cailliau
authors: Edith
authors: E
authors: Browaeys-Poly
authors: Jean-François
authors: JF
authors: Bodart
authors: Jean-Pierre
authors: JP
authors: Vilain
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D002713:Chlorine / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009865:Oocytes / Q000737:chemistry* / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D002713:Chlorine; D002118:Calcium