Fujita-Yoshigaki J
Department of Physiology, Nihon University School of Dentistry at Matsudo, Chiba, Japan.
Cell Signal. 1998 Jun;10(6):371-5. doi: 10.1016/s0898-6568(97)00178-2.
The process of membrane fusion is separated into three steps: docking, priming and fusion. The last fusion step of most regulated exocytosis is triggered by cytosolic free calcium (Ca2+). However, enzyme secretion from the parotid salivary glands is regulated by the accumulation of intracellular cAMP, although Ca2+ does augment the cAMP-induced secretion. The difference of the regulatory mechanisms is thought to be due to the brake points that will be passed upon stimulations. Vesicles of Ca2+-regulated exocytosis such as neurotransmission and norepinephrine release from chromaffin cells are waiting for the stimulation docked to the plasma membrane, and Ca2+ triggers the membrane fusion after the priming. In contrast, secretory granules of parotid acinar cells begin exocytosis with the docking step that may be regulated by cAMP. After the start of the docking, the exocytotic process of enzyme release runs a similar course to that of the neurotransmission: the priming and the Ca2+-enhanced fusion steps. Therefore, there are probably some common mechanisms involving the SNARE proteins both in Ca2+-regulated exocytosis and cAMP-dependent secretion.
对接、引发和融合。大多数受调控的胞吐作用的最后融合步骤由胞质游离钙（Ca2+）触发。然而，腮腺唾液腺的酶分泌受细胞内cAMP积累的调节，尽管Ca2+确实会增强cAMP诱导的分泌。调节机制的差异被认为是由于刺激时会越过的制动点。Ca2+调节的胞吐作用的囊泡，如神经传递和嗜铬细胞释放去甲肾上腺素，在停靠在质膜上等待刺激，Ca2+在引发后触发膜融合。相比之下，腮腺腺泡细胞的分泌颗粒在对接步骤开始胞吐作用，对接步骤可能受cAMP调节。对接开始后，酶释放的胞吐过程与神经传递的过程相似：引发和Ca2+增强的融合步骤。因此，在Ca2+调节的胞吐作用和cAMP依赖性分泌中，可能存在一些涉及SNARE蛋白的共同机制。
