Possible role of aldosterone and T-3 in development of amiloride-blockableSCC across frog skin in vivo

There are inconsistencies between the in vitro and in vivo effects of thyro id hormone and aldosterone (Aldo) on the development of an amiloride-blocka ble short-circuit current (SCC) across bullfrog skin [Takada, M., H. Yai, a nd K. Takayama-Arita. Am. J. Physiol. 268 (Cell Physiol. 37): C218-C226, 19 95]. To address this issue, tadpoles were raised in Aldo + T-3 An amiloride -blockable SCC developed across the skin before forelimbs appeared. Noise a nalysis of the characteristics (single-channel current, blocking and unbloc king rate coefficients, and apparent dissociation constant) of this amilori de-blockable Na+ channel showed that it really was of the adult type. A sim ilar SCC developed at stage XIX in the skin of tadpoles raised with Aldo al one. These results strongly support our hypothesis that the crucial hormone in the development of this SCC is Aldo but that a suppression mechanism at tenuates 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).