Interleukin 2 induces a rapid increase in intracellular pH through activation of a Na+/H+ antiport. Cytoplasmic alkalinization is not required for lymphocyte proliferation.
In several cell types, proliferation initiated by growth factors is associated with a rapid increase in cytoplasmic pH (pHi). This cytoplasmic alkalinization is due to the activation of an amiloride-sensitive Na+/H+ antiport. It is unclear whether growth factor-induced activation of the antiport or the resultant increase in pHi is the trigger for proliferation, an obligatory requirement for proliferation, or simply an associated phenomenon. Interleukin 2 (IL 2) acts as a growth factor for mitogen or antigen-stimulated thymus-derived (T) lymphocytes. In this study, we established that IL 2 produces an increase in pHi and determined whether this increase in pHi plays a role in the proliferative response to IL 2. Monitoring pHi with an intracellularly trapped, pH-sensitive, fluorescent dye, 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein, we demonstrated that IL 2 rapidly (less than 90 s) initiates an increase in pHi in IL 2-sensitive human and murine T cells. Because intracellular alkalinization requires extracellular Na+ and is amiloride-sensitive, it likely occurs through activation of the Na+/H+ antiport. Using partitioning of a weak acid, 5,5-dimethyl-2,4-oxazolidinedione, we confirmed that the IL 2-dependent increase in pHi is sustained for several hours and returns to near base-line levels by 18 h. We also investigated the consequence of preventing Na+/H+ exchange on the proliferative response induced by IL 2. IL 2-driven proliferation occurred in nominally bicarbonate-free medium in the presence of concentrations of amiloride analogs sufficient to inhibit the Na+/H+ antiport and prevent intracellular alkalinization. These data suggest that although the antiport is activated by binding of IL 2 to its receptor, intracellular alkalinization is not essential for IL 2-dependent proliferation. It seems unlikely that either cytoplasmic alkalinization or activation of the Na+/H+ antiport are triggers for T cell proliferation.
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004274:DNA, Recombinant; D005455:Fluorescent Antibody Technique; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007376:Interleukin-2 / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D051379:Mice; D011971:Receptors, Immunologic / Q000378:metabolism; D015375:Receptors, Interleukin-2; D017923:Sodium-Hydrogen Exchangers; D013601:T-Lymphocytes / Q000378:metabolism*
D002352:Carrier Proteins; D004274:DNA, Recombinant; D007376:Interleukin-2; D011971:Receptors, Immunologic; D015375:Receptors, Interleukin-2; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride