EVIDENCE FOR 2 INTRACELLULAR CALCIUM POOLS IN DICTYOSTELIUM - THE CAMP-INDUCED CALCIUM INFLUX IS DIRECTED INTO A NBD-CL- AND 2,5-DI-(TERT-BUTYL)-1,4-HYDROQUINONE-SENSITIVE POOL

Signal transduction in Dictyostelium for oriented movement and differe ntiation involves a fine tuning of the cytosolic Ca2+ concentration. W e have previously shown that cAMP binding to the cell surface receptor elicits two cellular events: (i) to enhance Ca2+ entry across the pla sma membrane; (ii) to increase Ca2+ uptake into Ca2+-sequestering orga nelles. Here we used permeabilised cells to show that cAMP-induced Ca2 + uptake in these cells was sensitive to the Ca2+ transport ATPase blo cker 2,5-di-(tert-butyl)-1,4-hydroquinone (BHQ) and the vacuolar H+-AT Pase inhibitor NBD-Cl. By contrast, bafilomycin A1 and vanadate, inhib itors of Ca2+ uptake into acidosomes in Dictyostelium, did not reduce the cAMP-induced Ca2+ uptake of permeabilised cells. GTPgammaS served as a tool to measure Ins(1,4,5)P3- (InsP3)-sensitive Ca2+ release. Fol lowing NBD-C] or BHQ treatment Ca2+ release was reversibly inhibited. We conclude that the cAMP-controlled Ca2+ influx is directed into a NB D-Cl and BHQ-sensitive compartment, which comprises the InsP3-releasab le pool. The acidosomal Ca2+ store seems to provide for additional Ca2 + if required.