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

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Abstract
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.