Passive potassium transport in LK sheep red cells. Modification by N-ethyl maleimide.

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Abstract
Passive K transport, as modified by N-ethyl maleimide (NEM), was studied in erythrocytes of the low-K (LK) phenotype of sheep. Brief (5-min) treatment with NEM at < 0.5 mM caused inhibition of passive K influx; NEM at concentrations > 0.5 mM caused stimulation of K influx. NEM had similar effects on K efflux. The treatments with NEM did not affect cell volumes (passive K transport in LK cells is sensitive to changes in cell volume). The stimulation of K transport by high [NEM] was also not a consequence of an effect on the metabolic state of the cells. Passive K transport in LK cells is dependent on Cl (it is inhibited in Cl-free media; it may be K/Cl cotransport). NEM had no effect on K influx in Cl-free (NO3-substituted) media. Pretreatment of the cells with anti-L antiserum (L antigen is found on LK cells and not on HK [higH K] cells) prevented stimulation of K influx by NEM, but did not prevent inhibition. Therefore, NEM modifies the Cl-dependent K transport pathway at 2 separate sites, a low-affinity site at which it stimulates, a high-affinity site at which it stimulates, and a high-affinity site at which it inhibits. Anti-L antibody prevents NEM action, but only at the low-affinity site.

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