Summary
Red blood cell (RBC) permeability (P, cm s-1) of human, dog, chick, duck, and Amphiuma means to 36Cl-, 14C-urea, and 3H2O was determined under self-exchange conditions (25°C, pH 7.2-7.5). PCl of all RBC species is 0.9-2.7 × 10-4 at CCl 127-150 mM. Purea is 0.83 × 10-6 in chick and 1.65 × 10-6 in duck RBC at Curea 1-500 mM. In human, dog, and Amphiuma RBC Purea is concentration-dependent at 1-1000 mM (Michaelis-Menten-like kinetics; K½ respectively 345, 173, 107 mM). At 1 mM urea Purea is 2.60 × 10-4 (human), 4.67 × 10-4 (dog), and 0.30 × 10-4 (Amphiuma). Diffusional water permeability Pd is 0.39 × 10-3 (Amphiuma), 0.84 × 10-3 (chick), 2.35 × 10-3 (human), 3.13 × 10-3 (dog), and 5.95 × 10-3 (duck). DIDS, DNDS, and phloretin inhibited PCl >99%. PCMBS, PCMB, and phloretin inhibited Purea >99% in human, dog, and Amphiuma RBC. Inhibition was absent in chick and duck RBC. PCMB and PCMBS inhibited Pd in human, dog, and duck, but not chick and Amphiuma RBC. Temperature dependence, EA, kJ mol-1, of PCl is 75 (Amphiuma), 100 (dog), and 118 (duck). EA of Purea is 70 (duck), and 53 (Amphiuma). EA of Pd is 35 (duck), and 32 (Amphiuma). Combining this study of PCl, Pd, Purea, and inhibition of Psolute with our previous RBC studies indicates that anion, urea, and water transporters respectively transport only chloride (all species), only urea (human, dog, Amphiuma), and only water (human, dog, duck). Water do not share the urea transporter with urea, and the solute transport is not coupled under normal physiological conditions.
