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  • Title: The correlation between ouabain binding and potassium pump inhibition in human and sheep erythrocytes.
    Author: Joiner CH, Lauf PK.
    Journal: J Physiol; 1978 Oct; 283():155-75. PubMed ID: 722573.
    Abstract:
    1. [3H]Ouabain binding to human and sheep red blood cells was shown to be specific for receptors associated with Na/K transport. Virtually all tritium binding was abolished by dilution with unlabelled drug. Saturation levels of binding were independent of glycoside concentration and were identical to those associated with 100% inhibition of K pumping. 2. [3H]Ouabain binding and 42K influx were measured simultaneously in order to correlate the degree of K pump inhibition with the amount of glycoside bound. Results by this method agreed exactly with those obtained by pre-exposing cells to drug, followed by washing and then measuring K influx. 3. Plots of [3H]oubain binding vs. K pump inhibition were rectilinear for human and low K (LK) sheep red cells, indicating one glycoside receptor per K pump site and functional homogeneity of pump sites. High K (HK) sheep red cells exhibited curved plots of binding versus inhibition, which were best explained in terms of one receptor per pump, but a heterogeneous population of pump sites. 4. External K reduced the rate of glycoside binding, but did not alter the relationship between binding and inhibition. 5. The number of K pump sites was estimated as 450--500 per human cell and 30--50 per LK sheep cell. HK sheep cells had 90--130 sites per cell, of which eighty to ninety were functionally dominant. The number of K pump sites on LK sheep cells was not changed by anti-L, although the maximum velocity of pump turnover was increased.
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