Attractant-induced changes and oscillations of the extracellular Ca++ concentration in suspensions of differentiating Dictyostelium cells.
We used a Ca++-sensitive electrode to measure changes in extracellular Ca++ concentration in cell suspensions of Dictyostelium discoideum during differentiation and attractant stimulation. The cells maintained an external level of 3-8 microM Ca++ until the beginning of aggregation and then started to take up Ca++. The attractants, folic acid, cyclic AMP, and cyclic GMP, induced a transient uptake of Ca++ by the cells. The response was detectable within 6 s and peaked at 30 s. Half-maximal uptake occurred at 5 nM cyclic AMP or 0.2 microM folic acid, respectively. The apparent rate of uptake amounted to 2 X 10(7) Ca++ per cell per min. Following uptake, Ca++ was released by the cells with a rate of 5 X 10(6) ions per cell per min. Specificity studies indicated that the induced uptake of Ca++ was mediated by cell surface receptors. The amount of accumulated Ca++ remained constant as long as a constant stimulus was provided. No apparent adaptation occurred. The cyclic AMP-induced uptake of Ca++ increased during differentiation and was dependent on the external Ca++ concentration. Saturation was found above 10 microM external Ca++. The time course and magnitude of the attractant-induced uptake of external Ca++ agree with a role of Ca++ during contraction. During development the extracellular Ca++ level oscillated with a period of 6-11 min. The change of the extracellular Ca++ concentration during one cycle would correspond to a 30-fold change of the cellular free Ca++ concentration.
D002118:Calcium / Q000502:physiology*; D002448:Cell Adhesion; D002449:Cell Aggregation; D002454:Cell Differentiation; D002633:Chemotaxis; D000242:Cyclic AMP / Q000502:physiology; D004023:Dictyostelium / Q000166:cytology*; D005110:Extracellular Space / Q000502:physiology; D010507:Periodicity
D000242:Cyclic AMP; D002118:Calcium