A MICROELECTRODE STUDY OF ELECTRICAL POTENTIALS IN FROG SKIN AND TOAD BLADDER.

Abstract

The results of a microelectrode study of the electrical potential of frog skin and toad bladder are reported. Employing extremely fine tipped microelectrodes and exploiting a new technique for penetrating these tissue membranes, the results obtained indicate that on penetration from the external (mucosal) surface the electrical potential increases rather smoothly with distance once the presumed functioning cellular layer has been reached. This finding is at variance with the findings of others who have reported that the total transmembranal potential difference is distributed in two more or less equal steps. With the microelectrode at various positions within these tissue membranes, as determined by the fractional resistance, the K + concentration in the solution bathing the internal (serosal) surface and the Na + concentration in the solution bathing the external (mucosal) surface have been varied. The resultant potential change measured by the microelectrode is compared with the total transmembranal potential change. The results show that the K + and Na + -sensitive functions previously envisaged to be located respectively at the internal and external bounding cell membranes of a single layer of cells are, in fact, more continuously and linearly distributed as a function of the fractional resistance. Furthermore, following a rapid change in the K + concentration bathing the internal (serosal) surface the time course of potential change in the microelectrode always lagged the total transmembranal potential change. This time lag is a function of the position of the microelectrode, increasing the further it is from the internal (serosal) surface as measured in terms of the fractional resistance. All these results suggest that the Koefoed-Johnsen-Ussing model in its simplest form is untenable and that any model envisaged must take into account various cytoplasmic structures and/or intercellular spaces.