Inhibition of cyclic GMP formation and aggregation in Dictyostelium by the intracellular Ca2+ antagonist TMB-8

AbstractAggregation in Dictyostelium discoideum was shown in previous studies employing EGTA to require Ca2+, but the intra- or extracellular site of action of this ion and its role in chemotaxis were not determined [1]. In this investigation we show that the intracellular Ca2+ immobilising agent TMB-8 does not affect binding of the signalling nucleotide, cAMP, to the cell surface receptors but abolishes the rapid accumulation of intracellular cGMP and subsequent chemotactic aggregation. We infer that movement of Ca2+ from membrane-bound stores is triggered by binding of cAMP to the cell-surface receptor and that this plays a primary role in stimulating cGMP formation and chemotaxis