Further investigations into membrane potentials in amoebae

Abstract

1. 1. The present work confirms the findings of Bingley and Thompson and Batueva that membrane potentials recorded from the tip of an advancing pseudopod are less negative than those recorded from the rear region. Photographic records are presented. 2. 2. Pseudopods streaming forward exhibit low potentials −24.5 mV s.d. ± 2.7 compared to the rear region −64.2 mV s.d. ± 4.4. 3. 3. Mechanical stimulation in the rear region produced a partial depolarization of the membrane. 4. 4. Breakage of a microelectrode while inside the cell was often followed by a positive membrane potential excursion of up to +70 mV. The cell expanded and water appeared to enter the cell. Photographic traces show the course of this potential change which shows some of the characteristics of an action potential. 5. 5. Electrode resistance was continuously monitored while membrane potentials were recorded. Increases in this during penetration suggest that there is only one resistive barrier, probably the cell membrane through which the electrode passes, whether it is in the pseudopod or rear region.