STIMULATION OF ACTIVE SODIUM TRANSPORT BY THE ISOLATED TOAD BLADDER WITH ALDOSTERONE IN VITRO*

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Abstract
The isolated urinary bladder of the toad transports sodium actively from its mucosal to its serosal surface. This phenomenon was measured isotopically and by the short-circuit current method on membranes exposed to aldosterone. At concentrations ranging from 2 to 25 x 10-7 M, aldosterone was capable of stimulating active sodium transport in vitro when applied to the serosal surface of the toad bladder. The hormonal effect became apparent after a latent period of 1 hour, whatever the concentration of aldosterone, and was roughly proportionate to the latter. It was less evident with preparations showing little spontaneous activity, and its was no longer demonstrable when the activity of the membrane had been increased by administration of sodium-retaining steroid to the toads. The existence of a latent period independent in duration from hormonal concentration, and the limited responsiveness of the isolated toad bladder to aldosterone suggest that the latter stimulates a rate-limiting step involved in active sodium transport via the synthesis or activation of a substrate.