Active and passive cation transport and L antigen heterogeneity in low potassium sheep red cells: evidence against the concept of leak-pump interconversion.

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Abstract
The L antigens in low potassium (LK) sheep red cells are apparently associated with separate Na+K+ pump and K+ leak pathways. The stimulating effect of anti-Lp on K+ pump flux is distinct from the action of anti-Ll on K+ leak flux, implying that K+ leak transport sites may not be converted into active pumps by the L antiserum. Treatment of LK red cells with trypsin completely abolished the stimulation of K+ pump flux and the enhancement of the rate of ouabain binding brought about by anti-L. That this effect is due to a total destruction of the Lp determinant associated with the LK pump was evident from the complete failure of anti-Lp to bind to trypsinized LK red cells. The Lp antigen can be effectively protected against the trypsin attack by prior incubation with anti-L, indicating that the sites for antibody binding and trypsin action may be closely adjacent at the structural level. Trypsin treatment did not interfere with the ability of anti-L1 to reduce ouabain insensitive K+ leak influx, nor did it prevent binding of anti-Lly, the hemolytically active L antibody which is probably identical with anti-Ll. The functional independence of the Lp and Ll sites was documented by the observation that anti-Ll still reduced K+ leak influx in LK cells with experimentally induced high K+ concentrations, at which K+ pump flux is fully suppressed, whether or not anti-Lp was binding to the Lp antigen associated with the LK pump.