Calcium transport in the cellular slime mould Dictyostelium discoideum

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Abstract
Transport of Ca2+ into amoebae of Dictyostelium discoideum was studied using 45Ca and a lanthanum stopping technique. Ca2+ uptake was found to be rapid and showed saturation kinetics. No difference was found in Ca2+ uptake between vegetative and aggregation competent cells, the V max for unstimulated amoebae being approx. 10 nmol/107 cells per min. Ca2+ uptake had the characteristics of passive facilitated diffusion using a saturatable carrier and NaN3 and ouabain were not inhibitory. The chemoattractants cAMP and folate, previously reported to stimulate the uptake of Ca2+ into amoebae, did not stimulate the rate of Ca2+ uptake by this carrier but increased the extent of Ca2+ taken up over the period 10–30 s after chemotactic stimulation. The significance of these findings for the function of Ca2+in chemotactic signalling is discussed.