Inhibition of aggregation in Dictyostelium by EGTA-induced depletion of calcium

During aggregation of Dictyostelium discoideum, amoebae move towards collecting centres emitting cyclic AMP. Previous work has indicated that Ca(2+) can affect the operation of various parts of the chemotactic mechanism but there are contradictory reports about the role or requirement for Ca(2+) during aggregation of intact amoebae. In this study we show that there is a requirement for Ca(2+) during this aggregation process. Addition of EGTA (7 mM) and in some cases extensive washing with EGTA is needed to see inhibition of aggregation. Considerable stores of Ca(2+) present within cells may explain the failure of some previous attempts to see a Ca(2+) requirement during aggregation.