NA+ GRADIENT-DEPENDENT PARA-AMINOHIPPURATE (PAH) TRANSPORT IN RAT BASOLATERAL MEMBRANE-VESICLES

  • 1 January 1983
    • journal article
    • research article
    • Vol. 227  (1) , 122-129
Abstract
The relationship between the transmembrane Na+ gradient and p-aminohippurate (PAH) transport was examined in isolated rat basolateral membrane vesicles. A 100 mM Na+ gradient (o .fwdarw. i [outside to inside]) accelerated the influx of 50 .mu.M [3H]PAH whereas similar gradients of choline+, K+, or Li+ did not. The Na effect was not due to a diffusion potential. The Na+ gradient (o .fwdarw. i) decreased the apparent Michaelis constant for PAH from 0.167 .+-. 0.016 to 0.054 .+-. 0.016 mM and increased the maximum flux rate from 116.00 .+-. 13.50 to 427.34 .+-. 98.96 pmol/mg/min. An "overshoot" of [3H]PAH influx (159 .+-. 4% of the equilibrium value) could be demonstrated only in the presence of a Na+ gradient (o .fwdarw. i) plus an opposing gradient of unlabeled PAH (i .fwdarw. o). Apparently, PAH transport and the Na+ gradient are functionally related. A model for cellular uptake of PAH by a Na+ gradient-dependent anion exchange mechanism is presented.