Ionic currents and cytoplasmic streaming in Amoeba proteus

Amoeba proteus may drive a current through themselves, and this current may determine the direction of cytoplasmic streaming. Cytoplasm streams from the more contracted tail or uroid region to the extending pseudopods. The positions of the uroid and pseudopods change as the amoeba changes direction. The membrane potential of the amoeba may change with location in the cell. This voltage gradient may regulate the magnitude and direction of cytoplasmic streaming. Bingley and Thompson (1962), recorded from amoebae using intracellular microelectrodes and reported that the membrane potential of the uroid region was more negative than that of the pseudopods. In contrast, Nuccitelli et al. (1977), using a vibrating probe, observed that current entered the uroid region and exited through the pseudopods. They concluded that the uroid region was more depolarized than the pseudopods. We revisited this issue by recording membrane potential simultaneously from two regions of the amoeba and by recording ionic currents using the two-electrode voltage clamp. Our data support the findings of Nuccitelli et al. Cytoplasm may stream from more depolarized to more hyperpolarized regions. Moreover, overshooting depolarizations of the cell may produce global cytoplasmic contractions and rounding of the amoeba.