Abstract
By means of a K+-sensitive electrode, the extracellular K+ concentration was monitored in cell suspensions of Dictyostelium discoideum. In aggregative cells the attractant cyclic AMP induced a transient release of K+. The response was detectable within 6-12 s and peaked at 30-40 s. The apparent rate of release amounted to 7 X 10(8)K+ ions per cell per min. Adenosine and 5' AMP, which are chemotactically inactive, did not elicit measurable K+ responses. The cyclic AMP-induced release of K+ depended on the state of differentiation of the cells. In undifferentiated cells cyclic AMP did not cause a measurable K+ release, whereas folic acid, a potent attractant at this cell stage, induced a weak but significant K+ response. The cyclic AMP-induced K+ release in aggregative cells was inhibited by K+-channel blockers such as quinine and tetraethylammonium. In suspensions of differentiated cells free running oscillations of the extracellular K+ concentration were observed. K+ oscillations were related to cyclic AMP oscillations and oscillations of the light-scattering properties of cells. Cells continuously released NH4+; however, cyclic AMP did not induce a measurable change of NH4+ release.
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