Thiol-dependent passive K/Cl transport in sheep red cells: II. Loss of Cl− and N-ethylmaleimide sensitivity in maturing high K+ cells

Abstract

A fraction of the passive, ouabain-insensitive K⁺ fluxes in mature low K⁺ (LK) but not in high K⁺ (HK) sheep red cells requires the presence of Cl⁻ anions and can be stimulated by volume expansion (Dunham, P.B., Ellory, J.C.,J. Physiol. (London) 318:511–530, 1981) or treatment with 2mm N-ethylmaleimide (NEM) (Lauf, P.K., Theg., B.E.,Biochem. Biophys. Res. Commun. 92:1422–1428, 1980). In the present study it is shown that reticulocytes of both anemic LK and HK sheep possess the Cl⁻-dependent K⁺ transport system which subsequently remains functional in mature LK but not in HK red cells. Kinetically, Cl⁻-mediated K⁺ fluxes of reticulocytes of LK sheep are different from mature red cells only in theirV _max values as measured in Na⁺ or choline⁺ media, while there is an apparently much lower affinity for external K⁺ ions in reticulocytes of HK sheep. N-ethylmaleimide stimulated K⁺ transport in the reticulocytes of both sheep genotypes suspended in Cl⁻ but failed to do so in NO ₃ ⁻ media. The data are interpreted in terms of their biochemical, physiologic, and genetic implications for the HK/LK transition in sheep red cells.