title: Pinocytosis and locomotion of amoebae: XVII. Influence of different cations on induced pinocytosis in Amoeba proteus.
abstract: The influence of various monovalent (Na(+), K(+), Li(+)), divalent (Ca(2+), Sr(2+), Mn(2+)), trivalent (La(3+), In(3+), Ta(3+)), and polyvalent cations (egg albumin) on the pinocytotic activity of starved Amoeba proteus was studied by a modified channel-counting method. Accordingly, a distinct stimulation of pinocytosis is induced by all substances in the following order of intensity: Mn(2+) < Ca(2+) < Sr(2+) < Li(+) < K(+) < Na(+) < Ta(3+) < In(3+) < La(3+) < egg albumin. Equimolar mixtures of different cations exhibit a simple additive influence on the induction capacity with the exception of Ca(2+) and Mn(2+) which both inhibit pinocytosis of other inorganic or organic ions at mM-concentrations (1-150 mM); on the other hand, experiments using μM-concentrations (10-0.001 μm) delivered no perceptible effect of low external Ca(2+) levels on induced pinocytosis. Independent of the nature or substantial composition of the induction solution pinocytotic activity is also suppressed in a linear way beyond total molarities of 150-200 μM and completely restrained at concentrations of 600 mM. Specific ionophors (A 23187, valinomycin) and inhibitors (D-600, isoptin hydrochloride, amilorid, tetraethylamonium chloride) of ionic transport increase and decrease the rate of Ca(2+)- and, to a lower extend, Na(+)- or K(+)-induced pinocytosis, respectively. In this connection, the general significance of endogeneous and exogeneous calcium for the control of membrane flow and actomyosin contraction is discussed.
authors.affiliation: Institute of Cytology, University of Bonn, Federal Republic of Germany.
authors.forename: W
authors.initials: W
authors.lastname: Stockem
authors.forename: H P
authors.initials: HP
authors.lastname: Klein