The effect of mastoparan on pancreatic secretion
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Cell secretion was studied using secretory granules and plasma membrane isolated for the pancreas. The exocytotic step in secretion is thought to involve the activation of electrolyte transport and the fusion of secretory membranes. The results showed that mastoparan, an amphiphilic peptide present in wasp venom, stimulated fusion between pancreatic zymogen granules and plasma membrane in the presence of guanosine triphosphate (GTP). This observation provides further evidence for the hypothesis that mastoparan acts by directly stimulating guanine nucleotide binding proteins (G-protein). In addition the results suggest that G-proteins are present on the zymogen granule membrane and provide control for exocytosis. Mastoparan, in high concentrations, caused non-specific lysis of the zymogen granules and did not cause any direct change in the rate of Cl” transport. This inability to influence electrolyte transport across the granule membrane demonstrates that an endogenous G-protein for the regulation of ion channels is not associated with the secretory vesicle. Mastoparan's ability to permeate membranes and activate fusion-associated G-proteins, similar to a receptor coupled reaction, makes it an important pharmacological tool in exocytosis and secretion research.