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

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Abstract
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.