Induction and Inhibition of Pinocytosis in Amoeba Proteus

Pinocytosis induced by different cations was studied by phase contrast in Amoeba proteus. Monovalent cations were more effective inducers the smaller the hydrated size of the ion (Cs>K>Na>Li). Divalent cations were less active inducers than monovalent ions and among the divalent ions tested calcium was unable to induce measurable pinocytosis. Tris+ possessed properties as an inducer similar to sodium although the intensity of Tris‐induced pinocytosis was greater. The sensitivity to the inducing cation decreased in proportion to the concentrations of calcium and hydrogen ions in the medium. Addition of a calcium chelating agent to the inducer decreased the maximum number of channels observed. Among the divalent cations present in the culture solution only calcium could restore the pinocytosis intensity to normal. The receptors in the cell membrane upon which inducing ions act are proposed to be negatively charged groups, the ionization of which varies with pH. Their availability to inducers is diminished when the calcium concentration of the medium is increased. A minimal calcium concentration is, however, required for a normal function of the channel forming system. The differene in activity between potassium and sodium in the induction of pinocytosis might be a factor controlling the intracellular content of these ions in the amoeba. The outward diffusion of potassium from the cell might explain the phenomenon of “spontaneous” pinocytosis.