Separative pathways for urea and water, and for chloride in chicken erythrocytes.

Abstract

Urea and water permeabilities of chicken erythrocytes are considerably lower than those of mammalian red cells. The permeabilities to urea, thiourea and to N-methylurea ( about 10-6 cm/s at 25.degree. C) were independent of concentration within a very broad range, and no evidence of interaction between transport of analogue molecules was found. The activation energies were between 17 and 19 kcal/mol, and urea transport was not inhibited by phloretin, which inhibits urea transport in mammalian red cells. The water permeability of chicken red cells (as measured by the diffusion of tritiated water) was 1.35 .times. 10-3 cm/s at 25.degree. C. The activation energy was 10 kcal/mol, and the water permeability was not affected by phloretin or parachloromercuribenzoate. The urea and water permeabilities of the chicken erythrocyte membrane are apparently similar to those of a non-porous bimolecular phospholipid membrane. Like the red cells of other animal species, the chicken red cell membrane contains an anion transport system, mediating a rapid exchange of chloride across the cell membranes. The pH dependence, temperature dependence, and sensitivity to inhibitors were similar to the properties of the anion transport system found in mammalian red cells. This transport system offers a highly specific pathway to the exchange of anions, without presenting an inspecific leak to the permeation of water and urea.