| Abstract: | Rap1 hasrecently been identified on the secretory granule membrane and plasmamembrane of rat parotid acinar cells (N. J. D'Silva, D. DiJulio, C. B. Belton, K. L. Jacobson, and E. L. Watson. J. Histochem. Cytochem. 45: 965-973, 1997). In thepresent study, we examined the cellular redistribution of Rap1following treatment of acini with isoproterenol (ISO), the -adrenergic agonist, and determined the relationship betweentranslocation and amylase release. In the presence of ISO, Rap1translocated to the cytosol in a concentration- and time-dependentmanner; this effect was not mimicked by the muscarinic agonist,carbachol. Translocation was maximal at 1 µM ISO and paralleledamylase release immediately after ISO stimulation. Rap1 translocationand amylase release were blocked by the -adrenergic antagonist,propranolol, whereas okadaic acid, a downstream secretory inhibitor,significantly blocked amylase release but did not inhibit Rap1redistribution. Results suggest that the translocation of Rap1 iscausally related to secretion and that the role of Rap1 in secretion isat a site proximal to the exocytotic event. |
