Role of membrane potential in the regulation of lectin-induced calcium uptake.

Incubation of lymphocytes with mitogenic lectins triggers Ca2+ uptake. This increase in free cytoplasmic Ca2+ is postulated to be an important signal in the initiation of DNA synthesis. Transmembrane fluxes of monovalent ions and changes in membrane potential are also associated with lectin-induced activation of lymphocytes. We have examined the relationship between extra-cellular monovalent ion substitution, the associated electrical potential changes (measured with cyanine dyes), phytohemagglutinin-induced Ca2+ uptake (measured with Quin-2) and proliferation in human T cells. The results show that (1) the magnitude of the increase in free cytoplasmic Ca2+ concentration is correlated with the extent of the lymphoproliferative response, (2) lectin-induced Ca2+ fluxes are sensitive to membrane potential, decreasing with depolarization, and are likely conductive, and (3) the presence of extra-cellular Na+ during incubation with phytohemagglutinin is not essential to mitogenic triggering.