Lysophosphatidylcholine reversibly arrests exocytosis and viral fusion at a stage between triggering and membrane merger.

Little is known of the events occurring between membrane fusion triggering and subsequent fusion steps. To dissect this process we applied a reversible inhibitor of membrane fusion, lysophosphatidylcholine, to arrest exocytosis and virus-mediated syncytia formation. Next Ca2+ or H+ (the respective fusion triggers) was administered and later removed. Then, inhibitor was withdrawn and fusion ensued, demonstrating that triggering causes the formation of an "activated state," which later develops into the fused state. Therefore, while different fusion processes utilize different triggers, the pivotal step involving membrane merger is trigger-independent and lipid-sensitive.