Mechanism of action of aldosterone on active sodium transport across toad skin.

Epithelium of the abdominal skin of the toad, Bufo marinus, has been studied by microelectrode impalement. Using an electrical equivalent circuit model, effective EMF's and specific conductances of the apical and basolateral membrane could be calculated. The skin was divided into 2 fragments for incubation in the presence, or not, of aldosterone (greater than or equal to 0.1 microM). After incubation overnight, sodium transport by the hormone-treated piece was increased 2.7-fold on average, compared to the untreated control. Concomitantly, conductance of the apical border increased more than 3-fold. Furthermore, mean conductance and electromotive force at the basolateral border increased by 80% and by 10%, respectively. Whether the latter changes merely represent delayed adaptation to increased apical conductance, cannot be settled from the data available.