Aldosterone increased the tubular volume in cortical collecting tubules (CCD) of rabbit kidney. It modulated the rate of cell sodium accumulation, under condition of ATPase inhibition (4 degrees C, in the absence of K+). In contrast, the relationship between Na+/K(+)-ATPase-dependent Na+ extrusion rate and intracellular Na+ concentration (Nai+) was similar in control, adrenalectomized, and aldosterone-treated adrenalectomized animals: Na+ extrusion rate increased with Nai+, up to 70 mM Nai+, and then plateaued. This indicates that aldosterone does not modify the characteristics of Nai(+)-dependent Na+ extrusion rate by the Na+/K(+)-ATPase pump in CCD.