Fast potential spike of frog skin generated at the outer surface of the epithelium.

Experiments were performed to test which structure of frog skin epithelium is responsible for the electrical excitation (fast, all-or-none potential spike) displayed by this tissue during stimulation with a current pulse. Preselected cells of the outer epithelial surface were punctured by microelectrodes under microscopical observation. The major part of the transepithelia resting resistance and the major part of the spike were recorded between microelectrode tip and outside bathing solution. A leak between microelectrode and punctured membrane is made responsible for the attenuation of spike amplitude observed under these recording conditions. It is shown that if the spike is generated at but one of the series membranes of the epithelium, this membrane must be at the outermost border of the tissue.