Na⁺/H⁺ antiporter has different properties in human B lymphocytes according to CD5 expression and malignant phenotype

In B chronic lymphocytic leukemia (B‐CLL) cells, lipopolysaccharide (LPS) and phorbol esters fail to activate the plasma membrane‐associated Na⁺/H⁺ anti‐porter and, subsequently, to elicit a rise in cytosolic pH. Since these events are thought to be a prerequisite for LPS‐induced proliferation of B normal lymphocytes, we analyzed the kinetic properties of Na⁺/H⁺ antiporter in B‐CLL cells as compared to both CD5⁻ and CD5⁺ normal B lymphocytes. In the present work we report that Na⁺/H⁺ exchange rate after acid loading is drastically decreased in B‐CLL cells, as compared to normal CD5⁻ B lymphocytes, although the antiporter affinity for external Na⁺ and internal H⁺ is not significantly different in both cell populations. Kinetic data account for a reduction in the number of operating antiport units in B‐CLL. The Na⁺/H⁺ antiporter of CD5⁺ normal B lymphocytes exhibits both an exchange rate and an ion affinity significantly higher than that observed in both CD5⁺ B‐CLL cells and CD5⁻ B normal lymphocytes, thus suggesting a possible explanation for their activated phenotype.