Effect of K⁺ on para aminohippurate transport by isolated perfused snake proximal renal tubules

Previous work showed that with 2 x 10^-5 M para aminohippurate (PAH) in bath of control Ringer (3 mM K⁺), net PAH transport occurred from bath to lumen against concentration gradient primarily in distal part of isolated perfused snake proximal renal tubules. Cell water [PAH] was greater than that in bath or lumen, suggesting active uptake into cells and passive diffusion into lumen. In present studies, removal of K⁺ from bath led within 40 min to depression of net PAH transport from bath to lumen, but transport still occurred against concentration gradient. Cell water [PAH] was markedly depressed, but was still greater than in bath or lumen. Since decreased cell water [PAH] and net PAH transport could have resulted from increased peritubular membrane permeability, this was determined from PAH efflux from tubules with oil filled lumens. These data suggest that removal of K⁺ depresses active uptake of PAH into cells. When K⁺ was restored to bath after 40 min perfusion without K⁺, net PAH transport doubled within 20 min. Cs⁺ could not replace K⁺ as requirement for PAH transport. Increasing K⁺ in bath to 40 mM depressed net PAH transport by about 50% in 20 min.