A study on sensing and adaptation in Dictyostelium discoideum: guanosine 3',5'-phosphate accumulation and light-scattering responses.

Abstract

Cells of D. discoideum respond to extracellular cAMP with marked changes in intracellular cGMP levels and light scattering. Defined temporal increases in cAMP were produced by the continuous addition of cAMP to agitated suspensions of cells; concomitant hydrolysis of cAMP by the cells subsequently established a constant, steady-state concentration. The cells responded to the initial increase in extracellular cAMP with a rapid increase in the intracellular cGMP concentration and a rapid decrease in light scattering. At cAMP input rates of 0.5-5 nM .times. s-1, the fast reactions of cGMP and light scattering had already relaxed while the cAMP concentration in the cell suspension was still increasing. The cells responded to constant concentrations of cAMP with constant elevated cGMP concentrations and constant decreased levels of light scattering. The results are consistent with the existence of 2 types of perception systems, one of which adapts to constant stimuli and one of which does not adapt.