The electrophysiology of cell fusion in the heliozoan, Echinosphaetium akamae, was studied by intracellular recording from two unicellular organisms undergoing fusion. Fusion was preceded by the electrical connection of axopodia of each cell to the cell body of the other. In the early stages of the fusion process, spikes evoked in one cell body failed to invade the other, but electrotonic potentials (subthreshold depolarizations) did pass to the other cell. When background depolarizing currents were injected into the organism into which the potentials had invaded, these potentials developed into spikes. In advanced stages of fusion, spikes were transmitted in both directions from one organism to the other, in the absence of polarizing current. At this time, application of appropriate hyperpolarizing currents to either of the two organisms prevented spikes produced in one from invading the other. These results suggest that in the early stage of fusion, relatively few axopodia were bridged by membrane fusion between paired cell bodies, and that the number of such bridged axopodia increased as fusion proceeded, allowing spikes to be transmitted between the two organisms.

This content is only available via PDF.