RADIATION TARGET SIZES OF THE NA,K-ATPASE AND PARA-AMINOHIPPURATE TRANSPORT-SYSTEM IN THE BASOLATERAL MEMBRANE OF RENAL PROXIMAL TUBULE

Abstract

Basolateral membrane vesicles made from rabbit kidney proximal tubules were frozen and irradiated with a high energy electron beam and the effects of irradiation on Na,K-ATPase activity, p-aminohippurate (PAH) transport, the membrane diffusion barrier and vesicle volume were measured. The vesicle volume and diffusion barrier were not significantly changed by radiation exposure. Na,K-ATPase activity was inactivated as a simple exponential function of radiation dose. Target size analysis of the data yielded a molecular size of 267 ± 17 kDa, consistent with its existence as a (αβ)2 dimer. The carrier-mediated PAH uptake by basolateral membrane vesicles was also inactivated as a function of radiation dose. A target molecular size of 74 ± 16 kDa was calculated for the PAH transport system. This study is the first measurement of the functional size of the organic acid transport system based directly on flux measurements.