SNARE PROTEINS ESSENTIAL FOR CYCLIC-AMP REGULATED EXOCYTOSIS IN SALIVARY-GLANDS

Rat parotid acinar cells secrete amylase through the stimulation of be ta-adrenoceptors followed by accumulation of intracellular cAMP. Howev er: it remains unclear at the molecular level how secretory granules f uss with the apical membranes. We have examined whether SNARE proteins are involved in exocytosis in the salivary glands, and have found tha t one of the SNARE proteins. VAMP-2. is localized at the secretory gra nule membrane of mt parotid acinar cells. Moreover, botulinum neurotox in B, which has endoprotease activity that cleaves VAMP-2, inhibited c AMP-dependent amylase release but did not inhibit basal secretion in t he absence of cAMP. Those results suggest that VAMP-2 is essential for cAMP-regulated exocytosis in rat parotid acinar cells. In contrast, b oth neurotoxins A and C1 (endoproteases that cleave SNAP-25 and syntax in1 respectively) failed to inhibit cAMP-dependent amylase release. Th erefore, neither SNAP-25 nor syntaxin 1 are involved in amylase secret ion in the parotid glands. Clarification of the mechanism of secretion will require the identification of proteins that interact and functio n cooperatively with VAMP-2. This approach may also reveal details of the molecular mechanism by which the cAMP facilitates secretion in oth er systems, including neurotransmission.