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Characterisation of an intracellular Ca2+ pump in Dictyostelium
E K Rooney1, J D Gross, M Satre
1Laboratoire de Biologie Cellulaire (URA 1130 CNRS), CEA, Département de Biologie, Moléculaire et Structurale, Centre d'Etudes Nucléaires de Grenoble, France.
Abstract:
Calcium uptake by microsomal membranes from the cellular slime mould Dictyostelium discoideum was measured using Calcium Green-2 as a fluorescent probe of external free Ca2+ concentration. High-affinity Ca2+ uptake was found to be completely inhibited by low concentrations of vanadate, but not by thapsigargin, suggesting that the activity is mediated by a Ca(2+)-ATPase distinct from sarco(endo)plasmic reticulum type of higher animal cells. On sucrose density gradients, Ca2+ uptake distributes with vacuolar proton pump activity and part of the observed Ca2+ uptake is dependent on the pH gradient generated by the vacuolar-type H(+)-ATPase, indicating that the Ca2+ pump is located on both acidic and non-acidic vesicles, possibly derived from the H(+)-ATPase-rich contractile vacuole complex.