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Passive potassium transport in LK sheep red cells. Modification by N-ethyl maleimide
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 less than 0.5 mM caused inhibition of passive K influx; NEM at concentrations greater than 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 cells) prevented stimulation of K influx by NEM, but did not prevent inhibition. Therefore, NEM modifies the Cl-dependent K transport pathway at two separate sites, a low-affinity site, at which it stimulates, and a high-affinity site, at which it inhibits. Anti-L antibody prevents NEM's action, but only at the low-affinity site.
Insights
N-ethylmaleimide (NEM) differentially affects passive potassium (K) transport in sheep erythrocytes. Low NEM concentrations inhibit K transport, while higher concentrations stimulate it, revealing distinct interaction sites on the K/Cl cotransporter.
Area of Science:
- Cell Physiology
- Membrane Transport
- Biochemistry
Background:
- Passive potassium (K) transport is crucial for erythrocyte function.
- Low-potassium (LK) sheep erythrocytes exhibit unique K+ transport characteristics.
- N-ethylmaleimide (NEM) is a chemical probe used to study protein sulfhydryl groups.
Purpose of the Study:
- To investigate the effects of N-ethylmaleimide (NEM) on passive K+ transport in LK sheep erythrocytes.
- To elucidate the mechanisms and binding sites of NEM's action on K+ transport.
- To determine the role of chloride (Cl-) and L antigen in NEM-mediated K+ transport modulation.
Main Methods:
- Treatment of LK sheep erythrocytes with varying concentrations of NEM.
- Measurement of passive K+ influx and efflux.
- Assessment of cell volume and metabolic state.
- Electrolyte substitution experiments (Cl- to NO3-).
- Pretreatment with anti-L antiserum.
Main Results:
- Low NEM concentrations (<0.5 mM) inhibited passive K+ influx and efflux.
- High NEM concentrations (>0.5 mM) stimulated passive K+ influx and efflux.
- NEM's effects were dependent on the presence of chloride (Cl-).
- Anti-L antiserum blocked NEM-induced stimulation but not inhibition of K+ transport.
Conclusions:
- NEM interacts with the Cl-dependent K+ transport pathway at two distinct sites: a high-affinity inhibitory site and a low-affinity stimulatory site.
- The L antigen is involved in the low-affinity stimulatory effect of NEM.
- These findings provide insights into the complex regulation of K+ transport in LK erythrocytes.