Fujita-Yoshigaki J, Dohke Y, Hara-Yokoyama M, Furuyama S, Sugiya H
Dept. of Physiology, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
Eur J Morphol. 1998 Aug;36 Suppl:46-9.
Rat parotid acinar cells secrete amylase through the stimulation of beta-adrenoceptors followed by accumulation of intracellular cAMP. However, it remains unclear at the molecular level how secretory granules fuse with the apical membranes. We have examined whether SNARE proteins are involved in exocytosis in the salivary glands, and have found that one of the SNARE proteins, VAMP-2, is localized at the secretory granule membrane of rat parotid acinar cells. Moreover, botulinum neurotoxin B, which has endoprotease activity that cleaves VAMP-2, inhibited cAMP-dependent amylase release but did not inhibit basal secretion in the absence of cAMP. These results suggest that VAMP-2 is essential for cAMP-regulated exocytosis in rat parotid acinar cells. In contrast, both neurotoxins A and C1 (endoproteases that cleave SNAP-25 and syntaxin 1 respectively) failed to inhibit cAMP-dependent amylase release. Therefore, neither SNAP-25 nor syntaxin 1 are involved in amylase secretion in the parotid glands. Clarification of the mechanism of secretion will require the identification of proteins that interact and function cooperatively with VAMP-2. This approach may also reveal details of the molecular mechanism by which the cAMP facilitates secretion in other systems, including neurotransmission.
大鼠腮腺腺泡细胞通过β - 肾上腺素能受体的刺激，继而细胞内cAMP积累来分泌淀粉酶。然而，在分子水平上，分泌颗粒如何与顶端膜融合仍不清楚。我们研究了SNARE蛋白是否参与唾液腺的胞吐作用，发现其中一种SNARE蛋白VAMP - 2定位于大鼠腮腺腺泡细胞的分泌颗粒膜上。此外，具有切割VAMP - 2的内切蛋白酶活性的肉毒杆菌神经毒素B抑制了cAMP依赖性淀粉酶的释放，但在无cAMP时不抑制基础分泌。这些结果表明，VAMP - 2对于大鼠腮腺腺泡细胞中cAMP调节的胞吐作用至关重要。相比之下，神经毒素A和C1（分别切割SNAP - 25和 syntaxin 1的内切蛋白酶）均未能抑制cAMP依赖性淀粉酶的释放。因此，SNAP - 25和syntaxin 1均不参与腮腺中的淀粉酶分泌。分泌机制的阐明将需要鉴定与VAMP - 2相互作用并协同发挥作用的蛋白质。这种方法也可能揭示cAMP促进包括神经传递在内的其他系统分泌的分子机制细节。
