Further studies on the effect of aldosterone on electrical resistance of toad bladder

The fall in transepithelial electrical resistance which accompanies aldosterone stimulation of short-circuit current (Isc) in toad urinary bladder has been studied further to evaluate the possible causal role of this response in hormonal stimulation of Na+ transport. A steady-state change in tissue conductance was found to depend upon both the simultaneous stimulation of transport by the steroid and the metabolic state of the tissue. Changes in metabolic state alone did not alter resistance. A sustained increase in Na+ transport, dependent on pretreatment with aldosterone and elicited by addition of glucose, could be obtained without a sustained decrease in resistance. Amiloride, an inhibitor of Na+ uptake, produced changes in Isc that were linearly correlated with its effects on tissue conductance. On the basis of the conductance-Isc relationship with amiloride, the Isc response to aldosterone was about two-fold higher than would be predicted from its effects on conductance alone. Despite the apparent lack of a simple quantitative dependence of the change in Isc on the change in conductance when the response is fully developed, the results suggest that conductance changes may mediate the initial or early stage of the response.