An investigation of extracellular ionic currents in Acetabularia acetabulum is presented. Utilising the vibrating electrode technique it is shown that there are large (up to 380μAcm−2) light-dependent and small (up to 10μAcm−2) light-independent extracellular ionic currents around Acetabularia. The current density was greatest at the rhizoid and diminished towards the developing apex where there was no measurable current.
Ion-replacement and ion-transport inhibitor studies indicated that Cl− was the main constituent of the light-dependent and light-independent currents. Calcium ions were found to contribute about 5–15% of the light-independent current and <1% of the light-dependent current, as deduced from cobalt inhibition studies. Possible mechanisms responsible for these phenomena are discussed briefly.