The permeability of red blood cells to chloride, urea and water

Abstract

This study extends permeability (P) data on chloride, urea and water in red blood cells (RBC), and concludes that the urea transporter (UT-B) does not transport water. Pof chick, duck, Amphiuma means, dog and human RBC to 36Cl-, 14C-urea and 3H2O was determined under self-exchange conditions. At 25°C and pH7.2-7.5, P Cl is 0.94×10-4-2.15×10-4cms- 1 for all RBC species at [Cl]=127-150 mmoll-1. In chick and duck RBC, Purea is 0.84×10-6 and 1.65×10-6cms-1, respectively, at [urea]=1-500mmoll-1. In Amphiuma, dog and human RBC, Purea is concentration dependent (1-1000 mmoll-1, Michaelis-Menten-like kinetics; K 1/2=127, 173 and 345mmoll-1), and values at [urea]=1 mmoll-1 are 29.5×10-6, 467×10- 6 and 260×10-6cms-1, respectively. Diffusional water permeability, Pd, was 0.84×10-3 (chick), 5.95×10-3 (duck), 0.39×10-3 (Amphiuma), 3.13×10-3 (dog) and 2.35×10-3cms-1 (human). DIDS, DNDS and phloretin inhibit PCl by >99% in all RBC species. PCMBS, PCMB and phloretin inhibit Purea by >99% in Amphiuma, dog and human RBC, but not in chick and duck RBC. PCMBS and PCMB inhibit Pd in duck, dog and human RBC, but not in chick and Amphiuma RBC. Temperature dependence, as measured by apparent activation energy, E A, of PCl is 117.8 (duck), 74.9 (Amphiuma) and 89.6 kJ mol-1 (dog). The EA of Purea is 69.6 (duck) and 53.3 kJ mol-1 (Amphiuma), and that of Pd is 34.9 (duck) and 32.1 kJ mol-1 (Amphiuma). The present and previous RBC studies indicate that anion (AE1), urea (UT-B) and water (AQP1) transporters only transport chloride (all species), water (duck, dog, human) and urea (Amphiuma, dog, human), respectively. Water does not share UT-B with urea, and the solute transport is not coupled under physiological conditions. © 2013. Published by The Company of Biologists Ltd.