Possible role of aldosterone and T3 in development of amiloride-blockable SCC across frog skin in vivo.

There are inconsistencies between the in vitro and in vivo effects of thyroid hormone and aldosterone (Aldo) on the development of an amiloride-blockable short-circuit current (SCC) across bullfrog skin [Takada, M., H. Yai, and K. Takayama-Arita. Am. J. Physiol. 268 ( Cell Physiol. 37): C218-C226, 1995]. To address this issue, tadpoles were raised in Aldo + T3. An amiloride-blockable SCC developed across the skin before forelimbs appeared. Noise analysis of the characteristics (single-channel current, blocking and unblocking rate coefficients, and apparent dissociation constant) of this amiloride-blockable Na+ channel showed that it really was of the adult type. A similar SCC developed at stage XIX in the skin of tadpoles raised with Aldo alone. These results strongly support our hypothesis that the crucial hormone in the development of this SCC is Aldo but that a suppression mechanism attenuates its effect on SCC development until it is removed by the increase in the serum concentration of thyroid hormone (which starts at stages XVIII-XIX in vivo).