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

Abstract

Aggregation 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.