Effect of aldosterone on active and passive conductance andE Na in the toad bladder

Summary It has been demonstrated previously that aldosterone increases the electrical conductance of the toad bladder in association with the stimulation of active sodium transport. In the present study the concurrent measurement of electrical quantities and ion tracer flux distinguishes effects on active and passive pathways. Lack of an effect on passive Na⁺ or Cl^– tracer flux in hemibladders preselected to eliminate large artefactual leaks indicates that aldosterone has no influence on physiological passive conductance. Thus, the enhancement of electrical conductance is entirely attributable to the active pathway. The magnitude of the increase in the active conductance was estimated. The data permitted also the comparison of effects on the flux ratio of Na⁺ at short circuit (f ₀) and the electrical potential difference adequate to abolish active sodium transport (E _Na). Even in membranes with minimal leakage the flux ratio does not reliably reflectE _Na. Aldosterone increased meanf ₀ from 11 to 22, but did not affectE _Na.