ROLE OF CELL-VOLUME VARIATIONS IN NA-K+-ATPASE RECRUITMENT AND()OR ACTIVATION IN CORTICAL COLLECTING DUCT/

The aim of this study was to examine whether cell volume variations co uld play a role in the previously reported Na+-K+-ATPase pump recruitm ent and/or activation induced by an increase in intracellular Na conce ntration (Nail in cortical collecting ducts (CCD). Isolated CCD from k idneys of aldosterone-repleted mice were incubated in hyper-, hypo-, o r isosmotic solutions with and without Na to modify Nai and cell volum e independently. Nai, cell volume, and the number of basolateral pumps were measured using Na-22, image analysis, and specific [H-3]ouabain binding, respectively. Ouabain-sensitive Rb-86 uptake was also measure d. In CCD with high Nai, pump recruitment and/or activation was observ ed only when an increase in tubular volume was associated with Na load . Pump recruitment and/or activation was also induced by cell swelling in the absence of Na load. Recruited and/or activated pumps display a n affinity for ouabain and a specific activity (ouabain-sensitive Rb u ptake per pump unit) similar to basal pumps. We conclude that 1) cell swelling is implied in the process of Nai-dependent pump recruitment a nd/or activation, 2) cell swelling can promote pump recruitment and/or activation independently of Na load, 3) basal and recruited and/or ac tivated pumps probably correspond to the same Na+-K+-ATPase isoform.