Membrane Potential and Conductance during Piocytosis Induced in Amoeba proteus with Alkali Metal lons

Abstract

An investigation of the relationship between the polarized state of the membrane and the onset and the intensity of pinocytosis was made in Amoeba proteus. Membrane potential and input resistance was in all instances found to decrease in approximate proportion to the number of channels when pinocytosis was induced by a variety of alkali metal ions at varying pH. Channels began to appear when the membrane was depolarized to -30 mV by the inducer of pinocytosis. With all inducers the maximum pinocytosis was encountered at membrane potentials close to zero. No positive potentials were recorded when the chloride salts of the inducing cations were used. At high concentrations of alkali ions a transient increase of the chloride permeability caused short-lasting hyperolarizations of the membrane. Inhibition of pinocytosis by Ca++ was accompanied by an increase of input resistance and membrane potential. The selectivity of the membrane to different alkali metal ions observed as changes in pinocytosis intensity, membrane potential and input resistance was found to vary with the concentration of the inducer and with the Ca++ concentration of the extracellular solution. Displacement of membrane bound Ca++ appeared to decrease the field strength of charged groups in the membrane altering its selectivity among alkali cations. The formation of pinocytotic channels is suggested to require translocation of Ca++ from the membrane into the cell and would therefore be closely related to the electrical properties of the amoeba.

Contractile basis of ameboid movement. VII. Aequorin luminescence during ameboid movement, endocytosis, and capping.

“…This rise in free calcium would then initiate solation-contraction coupling, forming fibrils derived from the cortex (72), which would then generate the forces required for channel formation. This proposed mechanism correlates well with many of the original suggestions by Brandt (14), Nachmias (46), Jeon and Bell (34), Josefsson et al (37), and recently by Klein and Stockem (38) (Fig . 11).…”

“…Brandt and Freeman (15) and Gingell and Palmer (27) demonstrated that the initiation of pinocytosis is accompanied by a decrease in electrical resistance of the plasmalemma, implying an increase in the ionic permeability . This might be related to the observation that the binding of pinocytosis inducers causes membrane depolarization (7,36,37) regulated by extracellular calcium and pH (32,37,51,52). Gingell (28) has suggested that the negative surface potential might be decreased when the inducers were bound and that this would directly affect the local membrane potential.…”

“…9 C), the formation of cortical actin fibrils (72), distinct electrical changes in the plasmalemma (14,15,37), and stimulation by primary messengers (pinocytotic inducers) (17, 32). Brandt and Freeman (15) and Gingell and Palmer (27) demonstrated that the initiation of pinocytosis is accompanied by a decrease in electrical resistance of the plasmalemma, implying an increase in the ionic permeability .…”

pH changes in pinosomes and phagosomes in the ameba, Chaos carolinensis.

“…Where Marshall's mc~lium (pH 4.0) is used, the composition is as follows: 0.26 mM KH~P0~, 0.05 mM MgSO(, 0.5 mM CaCI~, 0.14 mM KCI, pH 4.0 (sfight pH adjustments with 0.1 M HCl are performed at 4°C). Addition of KC1 brings the [K +] to that of normal Marshall's, deemed necessary because membrane potential, streaming velocity and pinocytic activity of amebae are affected by [K +] (4,5,20). Tetrahymena pyriformis, also obtained from Carolina Binloglcal Supply, are grown axenically in nutrient medium (1.5% Proteose peptone, 0.1% yeast extract, 0.2% dextrose).…”

Some Effects of Chemical Irritants on the Membrane of the Giant Amoeba

“…However, the culture conditions for the organisms in these investigations were different from those used in the present study and it is possible that discrepancies arise from differences in the characteristics of the recording system and electrodes used. A difference in the value for membrane potential probably resulting from a difference in the technique for impaling cells has been demonstrated in Amoeba proteus (Joseffson, 1966;Joseffson, Holmer & Hansson, 1975).…”