Summary: The calcium requirement for optimal growth of is between 0.05 and 2.5 mM. Media without Ca will not support growth though Ca-chelating agents, such as EDTA and EGTA, do not have any marked effect on Ca availability at the low pH used to culture this organism. The intracellular Ca concentration varies approximately 10-fold when the external Ca concentration is varied between 0.05 and 25 mM. Ca is concentrated in the mitochondrial and microsomal fractions, but the high concentration found in the cytosol suggests that considerable redistribution of Ca occurs during disruption and fractionation of the plasmodia. Ca uptake by intact microplasmodia occurs at rates which are comparable to those required for Ca uptake during growth and generation of new cell mass. This uptake process has two components: one non-saturable with Ca, and the other saturable with an apparent maximum velocity of 67 nmol Ca h (mg protein) and an apparent of 1.9 mM-Ca. As judged by [H]inulin uptake, part of the Ca uptake may be endocytotic.

Ionophores A23187 and Br-X537A stimulate Ca uptake. Uptake is inhibited by KCl, Mn and Sr at high concentrations, but is not sensitive to La at concentrations similar to Ca in the uptake medium. KCN and iodoacetic acid inhibit the transport, while cyto-chalasin B, verapamil, tetracaine and procaine have little or no effect.


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