Effect of collagenase and ouabain on renal cell volume in hypotonic media

Proximal straight tubules (S2 segments) swell rapidly in hypotonic media, but within a few minutes their volume returns toward control levels due to extrusion of K, Na, Cl, and water from the cytoplasm. In the present studies we determined the extent to which hydrostatic pressure (derived from the elastic tubule basement membrane (TBM) as the tubule enlarged in hypotonic medium) contributed to the regulation of cell volume. Removal of the TBM by collagenase had no effect on cell volume regulation in otherwise normal tubules. By contrast, tubules treated with ouabain, though they appeared to regulate their volumes in hypotonic media, were unable to do so in the presence of glycoside if the TBM had been removed with collagenase. This latter result is interpreted to show that hydrostatic pressure generated by extension of the TBM can cause "apparent" volume regulation when the sodium pump is blocked by ouabain. We conclude that normal proximal renal tubules regulate cell volume in hypotonic solutions by mechanisms that are dependent on the normal operation of the classical sodium pump.