An ATP-activated channel is involved in mitogenic stimulation of human T lymphocytes

Abstract

We investigated the effect of pharmacologic modulation of the ATP receptor on intracellular ion changes and proliferative response of human peripheral blood lymphocytes (PBLs) and purified T lymphocytes. Extracellular ATP (ATP(e)) triggered in these cells an increase in the cytoplasmic Ca2+ concentration ([Ca2+](i)) and plasma membrane depolarization. Whereas both Ca2+ release from intracellular stores and influx across the plasma membrane were detected in the whole PBL population, only Ca2+ influx was observed in T cells. In the presence of near physiologic extracellular Na+ concentrations (125 mmol/L), Ca2+ permeability through the ATP(e)-gated channel was very low, suggesting a higher selectivity for monovalent over divalent cations. The selective P(2Z) agonist benzoylbenzoic ATP (BzATP) increased [Ca2+](i) in the presence but not the absence of extracellular Ca2+ and also caused plasma membrane depolarization. The covalent blocker oxidized ATP (oATP), an inhibitor of P(2X) and P(2Z) receptors, prevented Ca2+ influx and plasma membrane depolarization, but had no effect on Ca2+ release from stores. Stimulation with ATP(e) alone had no significant effects on PBL 3H-thymidine incorporation. On the contrary, ATP(e) or BzATP had a synergistic effect on DNA synthesis stimulated by selective T-cell mitogens such as phytohemagglutinin, anti-CD3 monoclonal antibody, or allogeneic PBLs (mixed lymphocyte cultures). Treatment with oATP inhibited mitogenic stimulation by these receptor-directed agents but not by the combined application of the Ca2+ ionophore ionomycin and phorbol myristate acetate. Interleukin-2 partially relieved inhibition by oATP. These results suggest that human T lymphocytes express a plasma membrane channel gated by ATP(e) that is involved in mitogenic stimulation.