Electrophysiology of newt skin: effects of prolactin

Integumental transepithelial potential (TEP) was measured by both in vivo and in vitro (Ussing chamber) techniques in the same adult terrestrial-phase California newts (Taricha torosa). In both types of preparation, TEP showed a logarithmic relation to external sodium (as Na2SO4) concentrations between 0.1 and 10 meq/liter, with in vivo values exceeding in vitro values at all points. KM was ca. 1 and 5 meq/liter for the in vivo and in vitro preparations, respectively. When terrestrial-phase newts were treated with prolactin (PRL; 50 mIU/g/day), in vivo TEP declined significantly within 3 days. In vivo TEP versus [Na+]ext curves of recently collected aquatic-phase newts were found to be not significantly different from those of PRL-treated terrestrial-phase animals. Current/voltage (I/V) plots likewise showed that skin from aquatic-phase and PRL-treated terrestrial-phase newts was electrophysiologically alike. Estimates and calculations based on the I/V relationship suggest that PRL acts primarily to increase the epithelial electrical resistance in the transcellular pathway, with no effect on the electromotive force of the sodium pump.