Evidence for two intracellular calcium pools in Dictyostelium: the campinduced calcium influx is directed into a nbd-cland 2,5-di-(tert-butyl)-1,4 hydroquinone-sensitive pool

Abstract

Signal transduction in Dictyostelium for oriented movement and differentiation involves a fine tuning of the cytosolic Ca2+ concentration. We have previously shown that cAMP binding to the cell surface receptor elicits two cellular events: (i) to enhance Ca2+ entry across the plasma membrane; (ii) to increase Ca2+ uptake into Ca2+-sequestering organelles. Here we used permeabilised cells to show that cAMP-induced Ca2+ uptake in these cells was sensitive to the Ca2+ transport ATPase blocker 2,5-di-(tert-butyl)-1,4-hydroquinone (BHQ) and the vacuolar H+-ATPase inhibitor NBD-Cl. By contrast, bafilomycin A1 and vanadate, inhibitors of Ca2+ uptake into acidosomes in Dictyostelium, did not reduce the cAMP-induced Ca2+ uptake of permeabilised cells. GTPγS served as a tool to measure Ins(l,4,5) P3-(InsP3)-sensitive Ca2+ release. Following NBD-Cl or BHQ treatment Ca2+ release was reversibly inhibited. We conclude that the cAMP-controlled Ca2+ influx is directed into a NBD-Cl and BHQ-sensitive compartment, which comprises the InsP3-releasable pool. The acidosomal Ca2+ store seems to provide for additional Ca2+ if required.