Na transport compartment in rabbit urinary bladder.

The researchers used electron microprobe analysis to measure electrolyte concentrations. They collected data from rabbit urinary bladder under control and experimental conditions. Ouabain was applied to inhibit the Na/K-pump and observe cellular responses. In some trials, the apical side was kept Na-free to isolate transport mechanisms. Choline-Ringer's solution was used to test basolateral membrane permeability. Nystatin was introduced to assess its effect on ion exchange. The study compared electrolyte concentrations across epithelial layers. Dry weight content was also measured to evaluate cellular swelling or shrinkage.

Under control conditions, Na, K, and Cl concentrations were 11.6, 124.1, and 26.0 mmol/kg wet weight. Ouabain caused a 90 mmol/kg increase in Na and a 90 mmol/kg decrease in K. Dry weight content dropped by 6 g/100 g. Choline-Ringer's solution on the basal side reduced K by 60 mmol/kg. Nystatin with Na-sulfate Ringer's increased Na by 25 mmol/kg and Cl by 30 mmol/kg. Dry weight decreased by 4.5 g/100 g. Rb-Ringer's solution led to a 20 mmol/kg exchange of K for Rb. These changes occurred uniformly across all epithelial layers. The results suggest a lack of compartmentalization in Na transport.

The data support the idea that the rabbit urinary bladder functions as a syncytium in Na transport. The uniform changes across epithelial layers suggest no distinct transport compartments. The basolateral membrane appears permeable to Na, Cl, K, and choline. Ouabain and nystatin experiments confirm the role of active transport mechanisms. The study shows that Na-free conditions affect ion concentrations differently. The findings align with the hypothesis of a functional syncytium. The authors propose that transcellular and paracellular pathways operate in parallel. These results may inform future studies on epithelial transport mechanisms.