The sodium transport pool.

The sodium transport pool in epithelial cells represents sodium involved in active transport across the epithelium. There has been much controversy about the size of such a pool and even about its existence. Techniques for estimating the size of this pool are described. By analysis of toad bladder epithelial cells scraped from hemibladders mounted in chambers under a variety of conditions it has proved possible to detect and to quantify a sodium transport pool. Only about 20 percent of non-inulin space sodium measured flame photometrically is contained in this pool. This represents the total sodium entering cells from the mucosal medium, is in good agreement with the cellular sodium measured by the electron microprobe, and averages some 10-16 mmol/kg tissue H2O. Measurements of the pool in other tissues are considered.