Delineation of the Role of a Na +/Ca 2+ Exchanger in Regulating Intracellular Ca 2+ in T Cells

Abstract

One of the metabolic events that results from ligation of the CD3-TCR is an increase in [Ca 2+] i. The mechanisms that generate this rise in [Ca 2+] i are poorly understood, but involve mobilization of intracellular Ca 2+ stores and the movement of extracellular Ca 2+ into the cell. To examine the role of Na +/Ca 2+ exchange in the increase in [Ca 2+] i after CD3-TCR engagement, the effects of specific inhibitors of Na +/Ca 2+ exchange, DCB, CBDMB, and bepridil, were examined. Inhibitors of Na +/Ca 2+ exchange suppressed IL2 production and the rise in [Ca 2+] i in Jurkat cells stimulated by anti-CD3 mAb. Mobilization of intracellular Ca 2+ stores and mitogen-stimulated inositol phosphate production were not inhibited by these agents. Inhibitors of Na +/Ca 2+ exchange also inhibited mitogen responses of normal T cells and the sustained increase in [Ca 2+] i resulting from cross-linking class I MHC molecules, addition of PHA, or anti-CD3 mAb. Additional evidence for an important role of a Na +/Ca 2+ exchanger in generating increases in [Ca 2+] i after CD3 ligation was the finding that replacing extracellular Na + with Li +, that cannot be transported by the Na +/Ca 2+ exchanger, nearly abrogated the rise in [Ca 2+] i induced by cross-linking CD3. These results are consistent with the conclusion that a Na +/Ca 2+ exchanger is important in regulating changes in [Ca 2+] i that are critical for T cell activation.