Calcium regulates cAMP-induced potassium ion efflux in Dictyostelium discoideum.
The chemoattractant cAMP elicits a transient efflux of K+ in cell suspensions of Dictyostelium discoideum. This cellular response displayed half-maximal activity at about 1 microM cAMP and saturated at 100 microM cAMP, cAMP-stimulated K+ efflux, measured with a K+-sensitive electrode, depended on the extracellular free Ca2+ concentration ([Ca2+]0) and was maximal in the presence of EGTA. Usually more than 90% of the K+ release could be inhibited by the addition of Ca2+. Half-maximal reduction occurred at about 2 microM [Ca2+]0. Inhibition was also observed in the presence of caffeine or A23187, drugs known to elevate the intracellular free Ca2+ concentration ([Ca2+]i). Under conditions where [Ca2+]0 was maintained at a low level, half-maximal inhibition was 1 mM for caffeine and 3 microM for A23187. These results indicate that Cai2+ is involved in the regulation of K+ efflux. Simultaneous measurements of Ca2+ uptake and K+ efflux induced by cAMP as well as free running oscillations of both ions revealed that initiation and termination of Ca2+ uptake slightly preceded those of K+ efflux.
Aeckerle
S
S
Fakultät für Universität Konstanz, Konstanz (F.R.G.).
Malchow
D
D
D000818:Animals; D001692:Biological Transport; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling; D002454:Cell Differentiation; D002633:Chemotaxis; D000242:Cyclic AMP / Q000494:pharmacology / Q000502:physiology*; D004023:Dictyostelium / Q000502:physiology*; D004533:Egtazic Acid; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism
D010726:Phosphodiesterase Inhibitors; D002110:Caffeine; D004533:Egtazic Acid; D000242:Cyclic AMP; D011188:Potassium; D002118:Calcium