Thiol-dependent Passive K/Cl Transport in Sheep Red Cells: II. Loss of Cl- and N-ethylmaleimide Sensitivity in Maturing High K+ Cells

A fraction of the passive, ouabain-insensitive K+ fluxes in mature low Kr(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 2 mM 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 their Vmax 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 NO3- media. The data are interpreted in terms of their biochemical, physiologic, and genetic implications for the HK/LK transition in sheep red cells.