Volume changes in cells of the outer medulla during perfusion of the rat kidney.

Abstract

A method is described for perfusion of the rat kidney with a medium resembling rat plasma in its ionic constituents but with 3% polyvinylpyrrolidone (MW 44,000) replacing plasma proteins. In the early stages of perfusion, there was rapid swelling of tubular cells in the outer medulla, a low glomerular filtration rate and a low filtration fraction. After 30 min perfusion, the tubular cell volume in the outer medulla was normal, and filtration had increased and stabilized. Cell swelling and the low initial filtration fraction were prevented by adding 50 mM-mannitol to the basic medium, replacing 50 mM-NaCl with 50 mM-choline chloride or adding 5% human serum to the basic medium. Addition of human serum to the perfusion medium depressed fractional reabsorption of Na and K; Na from 0.94 .+-. 0.01 (SE [standard error] of mean) with the basic medium to 0.79 .+-. 0.02 with basic medium + 5% serum after 35 min perfusion; and K from 0.73 .+-. 0.04 with the basic medium to 0.37 .+-. 0.05 with the basic medium + 5% serum after 35 min perfusion. At the start of perfusion, effective internal osmolality of tubular cells of the outer medulla apparently was greater than that of cortical cells and of the basic medium. The presence of small amounts of plasma proteins in the perfusion medium had a marked effect on plasma cell membrane properties.