Mastoparan evokes exocytosis without Ca2+ movement in adrenal chromaffin cells

The secretagogue action of mastoparan, a tetradecapeptide from wasp venom, was studied in adrenal chromaffin cells. Pulsatile stimulation with mastoparan evoked a sharp transient release of CA in a dose-dependent manner, as measured by real-time monitoring system. The secretagogue action of mastoparan in these cells was apparently independent of extracellular Ca2+, and may not require the intracellular mobilization of Ca2+ since BAPTA failed to block its secretagogue action. Video-imaging data also suggested that mastoparan evokes CA release without an increase in the intracellular Ca2+. In addition, visualization of exocytotic events with video-enhanced light microscopy demonstrated that CA release evoked by mastoparan at relatively low concentration was indeed mediated by exocytotic process, not by cell lysis.