thioldependent passive kcl transport in sheep red cells ii loss of cl and nethylmaleimide sensitivity in maturing high k cells a fraction of the passive ouabaininsensitive k fluxes in mature low krlk but not in high k hk sheep red cells requires the presence of cl anions and can be stimulated by volume expansion dunham pb ellory jc j physiol london 318511530 1981 or treatment with 2 mm nethylmaleimide nem lauf pk theg be biochem biophys res commun 9214221428 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 nethylmaleimide 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 hklk transition in sheep red cells