M icroelectrode techniques were used to determine the Na+ and K+ transport properties of the collecting duct cell in the isolated cortical collecting duct (CCD) from rabbits 14 d after uninephrectomy (UNX); results were compared with those from sham-operated rabbits (control). UNX had no effects on plasma aldosterone levels. The CCDs from UNX rabbits exhibited structural hypertrophy. The lumen negative transepithelial voltage and the basolateral membrane voltage (VB) were elevated in the UNX group. Although the transepithelial conductance (GT) and the fractional apical membrane resistance (fRA) were not different between the two groups, the conductances of the apical and the basolateral membranes were increased, and the tight junction conductance was decreased in the UNX group. The amiloride-sensitive changes in apical membrane voltage (VA), fRA, and GT were greater in the UNX group. The changes in VA upon raising the perfusate K+ concentration and the changes in VA and GT upon addition of Ba2+ to the perfusate were elevated in the UNX group. Upon raising K+ in the bath, a large depolarization of VB was observed in the UNX group. Lowering the bath Cl- resulted in a small depolarization of VB in the UNX group. Addition of Ba2+ to the bath in the UNX group caused the VB to hyperpolarize in parallel with decreases in GT and fRA whereas in the control group it had no effect on VB. Addition of ouabain to the bath resulted in a large depolarization of VB in the UNX group. We conclude that (a) UNX stimulates conductances of Na+ and K+ in the apical membrane, active Na(+)-K+ pump activity, and K+ conductance in the basolateral membrane, independently of plasma aldosterone; (b) The basolateral membrane in the tubules of UNX rabbits is more selective to K+; and (c) the hyperpolarization of VB upon UNX may increase passive K+ entry into the cell across the basolateral membrane.