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-Adrenergic-induced cytosolic redistribution of Rap1 in rat
parotid acini: role in secretion
Departments of 1 Oral Biology and 2 Pharmacology, University of Washington, Seattle, Washington 98195
Rap1 has
recently been identified on the secretory granule membrane and plasma
membrane 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 the
present study, we examined the cellular redistribution of Rap1
following treatment of acini with isoproterenol (ISO), the
-adrenergic agonist, and determined the relationship between
translocation and amylase release. In the presence of ISO, Rap1
translocated to the cytosol in a concentration- and time-dependent
manner; this effect was not mimicked by the muscarinic agonist,
carbachol. Translocation was maximal at 1 µM ISO and paralleled
amylase release immediately after ISO stimulation. Rap1 translocation
and amylase release were blocked by the
-adrenergic antagonist,
propranolol, whereas okadaic acid, a downstream secretory inhibitor,
significantly blocked amylase release but did not inhibit Rap1
redistribution. Results suggest that the translocation of Rap1 is
causally related to secretion and that the role of Rap1 in secretion is
at a site proximal to the exocytotic event.
small GTP-binding protein; translocation; salivary gland; exocrine secretion; amylase release
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