Role of monovalent ions in the reabsorption of fluid by isolated perfused proximal renal tubules of the rabbit.

Proximal convoluted tubules were dissected from rabbit kidneys and perfused in vitro in order to determine the effect of monovalent ions on fluid absorption and transepithelial voltage. Replacement of sodium in the perfusate and bath by lithium, tetramethyl ammonium or choline caused the rate of fluid absorption and voltage to fall to near zero. Replacement of potassium in the bath by sodium had the identical effect. Replacement of chloride by nitrate or perchlorate had comparatively little effect. The results are consistent with the generally held view that active sodium transport (mediated by a Na- and K- activated adenosine triphosphatase) is the primary process responsible for the absorption of the fluid and the voltage. Replacement of bicarbonate in the perfusate and bath by chloride caused the rate of fluid absorption to decrease by 33%. The possible relation between sodium transport and bicarbonate is discussed.