Volume of Renal Cortical Cytoplasm in Rabbits,and Basolateral Transport Gradients of Cycloleucine and p -Aminohippurate

Abstract

Abstract

The intracellular volume of distribution of the nonmetabolizable sugar derivative 3-O-methylglucose was determined in the renal cortex of diuresing rabbits. This sugar is not well reabsorbed from the lumen, but is readily taken up across the basolateral cell membranes by an apparently flow-limited, nonconcentrative process. The ratio of distribution volumes of nonfiltered 3-O-methylglucose and inulin, therefore, equals the ratio of their mean artery-vein transit times. An intracellular and presumably cytoplasmic volume for 3-O-methylglucose of 0.13 ml/g was thus determined in the cortex of rabbits undergoing mannitol diuresis; similar values were obtained with three other less direct approaches. Availability of a reliable value permitted calculation of the activity gradients against which para-aminohippurate and the neutral amino acid cycloleucine can be accumulated at the basolateral membrane in vivo; both gradients equal about 6:1. This finding underlines the active nature of basolateral amino acid uptake and points to a further characteristic common to the organic anion and the cycloleucine carrier systems.