Action of ouabain on bioelectric properties and ion content in toad urinary bladder

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Abstract
In toad bladders exposed to Na containing serosal solutions, inhibition by ouabain of short-circuit current and potential difference was accompanied by a loss of tissue K and an uptake of Na from the serosal solution. If the serosal solution was Na-free, ouabain inhibited the bioelectric phenomena but tissue Na and K were not greatly modified. Therefore, the inhibitory effect of ouabain on potential difference appear to be more closely related to the inhibition of active ion transport than to tissue electrolyte content. When Cl was replaced by sulfate and a 200-mv potential step (serosa negative to mucosa) applied across the bladder, ouabain caused an entry of mucosal Na into the epithelium across the apical surface and a loss of K, despite the absence of serosal Na. The results are consistent with a Koefoed-Johnsen and Ussing model in which an electrogenlc pump coexists in parallel with the K-permeable channel of the basal barrier of the epithelium.