Spectrofluorimetric and image recordings of spontaneous and lectin-induced cytosolic calcium oscillations in Jurkat T cells

Intracellular variations in Ca 2+ concentrations have been measured in single Jurkat T lymphocyte variants (77 6.8 and E6.1) using Fura-2 as a probe. Under basal conditions, the cytosolic Ca 2+ level is stable but some cells show spontaneous Ca 2+ oscillations (frequency, 0.30 ± 0.06 Hz). These oscillations are sensitive to the external concentration of Ca 2+ since they can no longer be observed when the bathing solution is replaced (superfusion) with a Ca 2+-free medium or when a Ca 2+ chelator (EGTA) is added. various changes in the cytosolic concentration of Ca 2+ ([Ca 2+] i) can be observed when the cells are exposed to the mitogenic lectin phytohemagglutinin (PHA, 80 nM). For instance, in the case of non-oscillating cells, the lectin induces either a rapid increase in [Ca 2+] i that is followed by a sustained response (plateau) or it triggers Ca 2+ spikes. In the case of experiments done in Ca 2+-free medium, only the initial spike was observed. In the case of spontaneously oscillating cells, PHA induces a rapid increase in [Ca 2+] i that is followed by a piateau where oscillations are absent. In every case, the PHA-dependent Ca 2+ response is abrogated in a Ca 2+-free medium. Computer simulations based on the model of Goldbeter et al. [27] show that the various Ca 2+ responses of Jurkat cells are related to the cytosolic level of free Ca 2+. Video imaging analyses show that the cellular Ca 2+ responses are not homogeneous whether the observations are made in spontaneously oscillating Jurkat cells or when they are exposed to PHA.