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.