Lack of specificity of melittin as a probe for insulin release mediated by endogenous phospholipase A2 or lipoxygenase.

摘要: The effects of the basic polypeptide melittin on islet phospholipid degradation and insulin release were studied in static incubations intact rat islets as a possible model endogenous phospholipase A2 (PLA2) activation. Melittin (2 micrograms/ml) increased [3H]-arachidonic acid [( 3H]-AA) from prelabeled (at 1.7 mM glucose) to 371% basal values. Concomitantly, induced phospholipids labeled with [3H]-AA or [14C]-stearic acid, led accumulation stearate-labeled (but not AA-labeled) lysophosphatidylcholine (LPC, 605% control). These findings suggested, for first time islets, presence activation PLA2. Under identical conditions, initiated secretion manner that represented stimulation physiologic exocytosis--that is, it was dose-dependent, reversible (albeit slowly), unassociated impairment other processes (i.e. response 16.7 glucose after removal drug) inhibitable by reduced ambient temperature. effect seemed be independent extracellular Ca2+ influx mobilization intracellular stores but blocked nickel lanthanum, indirectly suggesting this cationic amphiphile might involve superficial pool Ca2+. Unexpectedly, melittin-induced least at low concentrations) greatly consistently altered battery inhibitors PLA2 enzymes affecting AA oxygenation. Furthermore, significant contamination bee venom commercially-available preparation found, could pure PLA2, probably through generation lysophospholipids. Although estimates amount suggested such insufficient explain some hydrolysis caused melittin, we conclude agent does serve specific probe role lipoxygenation hormone release.