Voltage-dependent reversal of anodic galvanotaxis in Nyctotherus ovalis

Aerobic and anaerobic ciliates swim towards the cathode when they are expos ed 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 respo nse is not due to backward swimming. Rather the ciliates turn around and or ient to the cathode with their anterior pole. Exposure to various cations, chelators, and Ca2+-channel inhibitors suggests that Ca2+-channels similar to the "long lasting" Ca2+-channels of vertebrates are involved in the volt age-dependent anodic galvanotaxis. Evidence is presented that host-dependen t epigenetic factors can influence the voltage-threshold for the switch fro m anodic to cathodic swimming.