Ionic Distribution in Amoeba Proteus

The intracellular concentrations of K, Na, Ca and Cl in Amoeba proteus are 24·83, 1·08, 2·93 and 9·73 mM/kg cells respectively. Intracellular Na is always slightly higher than that of the external medium when external Ca is low. Addition of Ca to the medium reduces the intracellular concentration of Na by decreasing the permeability of the plasmalemma to Na. The membrane potential of Amoeba proteus in Prescott-James medium is −89·5 mV and is sensitive to changes in both external K and external Na when external Ca is low. Intracellular Na and K are both sensitive to the addition of CN to the external medium. Both Na and K are actively transported in the amoeba ; K is actively accumulated from the external medium and Na is actively expelled from the cell. It has been suggested that the effects of Ca on Amoeba proteus, i.e. reduction of PNa, reduced internal concentration of Na, reduced unidirectional Na and K influxes, and increased membrane resistance are due to Ca binding to the plasmalemma.