Thyroxin specifically stimulates anuran larvae epidermal sodium pump during metamorphosis

Development of aldosterone-stimulation of short-circuit current across larval frog skin

The short-circuit current (SCC) across isolated skin from bullfrog larvae in developmental stage XXI was small and insensitive to amiloride. Overnight incubation of this tissue with 10(-6) M aldosterone stimulated the SCC from 1.35 +/- 0.55 to 14.55 +/- 4.12 microA.cm-2 with 11.18 +/- 4.46 microA.cm-2 being blocked by 100 microM amiloride. Histologic examination of aldosterone-treated skins revealed a separation of the apical cell layer from the underlying epidermis that was not seen in untreated preparations. The onset of amiloride-sensitive Na+ transport thus coincided with the exposure of the apical surface of newly differentiated epithelial cells. Similar results were obtained with skin from stage XXI larvae whose rate of metamorphosis had been stimulated by 10 micrograms.1-1 thyroxine (T4) but not with skin from T4-treated larvae in stages XIX and XX. Fluctuation analysis of the amiloride-sensitive SCC of the above preparations failed to show a consistent Lorentzian component in the power-density spectrum. Fluctuation analysis was possible on skins from larvae whose development had been accelerated by 7-9 days treatment with 10 micrograms.l-1 triiodothyronine (T3). Aldosterone treatment of these tissues resulted in a significant increase in Na+ channel density.