Voltage-Dependent Reversal of Anodic Galvanotaxis in Nyctotherus ovalis

Aerobic and anaerobic ciliates swim towards the cathode when they are exposed to a constant DC field. Nyctotherus ovalis from the intestinal tract of cockroaches exhibits a different galvanotactic response: at low strength of the DC field the ciliates orient towards the anode whereas DC fields above 2-4 V/cm cause cathodic swimming. This reversal of the galvanotactic response is not due to backward swimming. Rather the ciliates turn around and orient to the cathode with their anterior pole. Exposure to various cations, chelators, and Ca 2+ -channel inhibitors suggests that Ca 2+ -channels similar to the long lasting Ca 2+ -channels of vertebrates are involved in the voltage-dependent anodic galvanotaxis. Evidence is presented that host-dependent epigenetic factors can influence the voltage-threshold for the switch from anodic to cathodic swimming.