Effect of lanthanum on pinocytosis induced by cations in Amoeba proteus

Lanthanum chloride (greater than or equal to 10(-5) M) induced pinocytosis in normal and at greater than or equal to 10(-4) M 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+++ stimulated or inhibited other types of pinocytosis. Thus all concentrations of La+++ inhibited sodium induced pinocytosis while high concentrations (greater than 10(-3) M) 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 a K+-like inducer 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.