Oscillations of Ca + + concentration during the cell differentiation of Dictyostelium discoideum: Their relation to oscillations in cyclic AMP and other components

Abstract

Periodic cyclic-AMP pulses control the cell aggregation and differentiation of Dictyostelium discoideum. Another component required for the aggregation and differentiation of these cells appears to be extracellular Ca + +. Oscillations in extracellular Ca + + concentration were investigated in suspensions of differentiating cells. We observed spike-shaped and sinusoidal Ca + + oscillations. In the course of differentiation, spike-shaped Ca + + oscillations preceded sinusoidal oscillations, and no phase change occurred at the transition from spike-shaped to sinusoidal Ca + + oscillations. Spike-shaped and sinusoidal Ca + + oscillations were related to oscillations in (1) the cyclic-AMP and cyclic-GMP content of cells, (2) the light-scattering properties of cells, and (3) the extracellular pH. Spikeshaped Ca + + oscillations were observed together with cyclic-AMP oscillations. The minima of the extracellular Ca + + concentration trailed the maxima of the cyclic-AMP concentration by about 30 s. Sinusoidal Ca + + oscillations were not accompanied by measurable cyclic-AMP oscillations. The amplitudes of the sinusoidal Ca + + oscillations were smaller than those of the spike-shaped Ca + + oscillations. A Ca + + oscillation of small amplitude (instead of a spike-shaped oscillation) was observed when one cyclic-AMP spike was skipped. Our results provide evidence for the existence of a sinusoidal cyclic-AMP-independent Ca + + oscillation of small amplitude, and they also suggest that spike-shaped Ca + + oscillations may be superimposed on such small-amplitude oscillations. When D. discoideum cells produce cyclic-AMP spikes, the uptake of additional Ca + + is induced, resulting in Ca + + oscillations of a large amplitude.