The effect of anti-L on ouabain binding to sheep erythrocytes

Summary

Binding of³H-ouabain was studied in high potassium (HK) and low potassium (LK) sheep red cells. In particular, we investigated the effect of anti-L, an antibody raised in HK sheep against L-positive LK sheep red cells, on³H-ouabain binding and its relation to K⁺-pump flux inhibition in LK cells. HK cells were found to have about twice as many³H-ouabain binding sites and a higher association rate for³H-ouabain than homozygous LL-type LK cells. The number of³H-ouabain molecules bound to heterozygous LM-type LK cells is lower than that on LL cells, but the rate of ouabain binding is between that of HK and LL red cells. A close correlation was observed between the rates of³H-ouabain binding and fractional K⁺-pump inhibition. Exposure of LM and LL cells to anti-L did not affect the number of³H-ouabain molecules bound at saturation, but increased the rates of glycoside binding and K⁺-pump inhibition proportionately, so that for LK cells in the presence of anti-L, the rates of the two processes approximate those of HK cells. These data exclude the possibility that anti-L generates entirely new pump sites in LK sheep red cells, but suggest that the antibody increases the affinity of the existing Na⁺−K⁺ pumps for the glycoside.