Transepithelial potentials in Hydra.

There is a maintained electrical potential of 15 to 40 millivolts across the two epithelial layers forming the body wall of Hydra, the inside of the animal being positive. Negativegoing (depolarizing) spikes are recorded spontaneously and sometimes in response to depolarizing current pulses. These spikes usually overshoot the zero potential level. The large size of the spikes and the orientation of the potential difference across the body wall indicate that this electrical activity is epithelial rather than nervous in origin.