Early transmembrane events in tumor necrosis factor and lymphotoxin-induced cytotoxicity.

We have studied early transmembrane events in tumor necrosis factor (TNF) and lymphotoxin (LT)-induced cytotoxicity by means of stopped-flow fluorometry with 3 different fluorescent probes. Both TNF and LT caused an increase in the membrane fluidity of the target cells (L X P3 cells). After this event, there was a low level of calcium influx from the external medium into the target cells. On the other hand, the release of calcium from intracellular stores in the target cells was negligible. These sequential events, however, were not observed when mutant LT molecules which lacked the lytic activity were used.