Para aminohippurate (PAH) transport and fluid absorption were studied in isolated, perfused frog (Rana catesbeiana) proximal renal tubules. With 2x10-5 M PAH in the bath, tubule fluid to bath (TF/B) concentration ratios averaged 3.0 and net secretion averaged 746x10-15 mol min-1 mm-1 in the proximal tubule. Net PAH secretion did not vary with perfusion rate. During PAH secretion, cell water PAH concentration exceeded that in the tubular fluid or bath, suggesting active transport into cells and subsequent diffusion into lumen. In accordance with this concept, luminal membrane permeability (3.8x10-5 cm s-1) calculated from perfusion studies was about 6 times greater than peritubular membrane permeability (0.66x10-5 cm s-1) determined from studies of PAH efflux from tubules with oil filled lumens. Net transepithelial PAH transport saturated at bath concentration of about 6x10-5 M. Addition of 20 mM urea to PAH bath concentration of 2x10-5 M reduced net PAH secretion by 32%. Fluid absorption in proximal tubules averaged 0.34 nl min-1 mm-1. Ouabain (10-4, 10-5 or 10-6 M) added to bath blocked fluid absorption. Fluid absorption was partially restored following removal of ouabain.
|Original language||English (US)|
|Number of pages||8|
|Journal||American Journal of Physiology|
|State||Published - Dec 1 1976|
ASJC Scopus subject areas
- Physiology (medical)