Interleukin 2 increases T lymphocyte membrane mobility before the rise in cytosolic calcium concentration

Using stopped-flow fluorometry with three different fluorescence probes [2-[(1-pyrenyl-butyryl)oxy]stearic acid, chlortetracycline and Quin 2], we have studied initial stage of T lymphocyte activation after interleukin 2 (IL-2) binding to a specific cell-surface receptor. After IL-2 binding to cytotoxic T lymphocyte (IL-2-dependent mouse LC7 and CTLL-2 cells), membrane mobilities of the cells increased first (4.5 +/- 0.3 s-1 for LC7 and 3.8 +/- 0.2 s-1 for CTLL-2), then calcium was released from intracellular stores into the cytoplasm (1.6 +/- 0.1 s-1 for LC7 and 2.1 +/- 0.1 s-1 for CTLL-2), and lastly, calcium was transported from the external medium into the cytoplasm (1.3 +/- 0.1 s-1 for LC7 and 1.5 +/- 0.1 s-1 for CTLL-2). The slowest process, the calcium influx from the external medium, was suppressed in the presence of a calcium channel blocking agent (verapamil). These observations give us a new information to discuss a model in T lymphocyte activation after IL-2 binding to cell-surface receptors.