Effects of Lanthanum on Pinocytosis Induced by Cations inAmoeba proteus

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Abstract
Lanthanum chloride (≥ 10‐5M) induced pinocytosis in normal and at ≥10‐4M in Ca++‐deficient amoeba. With respect to the Ca++‐requirement of the pinocytotic response low and high concentrations of La+++had effects like Na+and K.+, respectively. The concentration of La+++and the concentration and species of inducing monovalent cation determined whether La+++stimulated or inhibited other types of pinocytosis. Thus all concentrations of La+++inhibited sodium induced pinocytosis while high concentrations (> 10‐3M) stimulated and low concentrations diminished potassium induced pinocytosis. Only the latter effect required the presence of Ca++. In the presence of La+++other inducers acted either like K+or Na+. Inducers may cause channel formation by opening a pore for Ca++in the plasma membrane, Na+‐like inducers being less effective than K+‐like inducers, and by releasing Ca++into the cytoplasm from the glycocalyx (Na+‐like inducers) or from the entire cell membrane (K+‐like inducers). La+++may diminish the effect of Na+‐like inducers and vice versa by direct competition for sites in the glycocalyx and the effect of K+‐like inducers by redistribution of Ca++in the cell surface. At high concentrations or in the presence of a K+‐like inducer La+++may enter the Ca++pore, release Ca++from the interior of the membrane and so induce or stimulate pinocytosis.

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