Catalán Marcelo A, Kondo Yusuke, Peña-Munzenmayer Gaspar, Jaramillo Yasna, Liu Frances, Choi Sooji, Crandall Edward, Borok Zea, Flodby Per, Shull Gary E, Melvin James E
Secretory Mechanisms and Dysfunction Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892;
Secretory Mechanisms and Dysfunction Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892; Department of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu, Fukuoka 803-8580, Japan;
Proc Natl Acad Sci U S A. 2015 Feb 17;112(7):2263-8. doi: 10.1073/pnas.1415739112. Epub 2015 Feb 2.
Activation of an apical Ca(2+)-activated Cl(-) channel (CaCC) triggers the secretion of saliva. It was previously demonstrated that CaCC-mediated Cl(-) current and Cl(-) efflux are absent in the acinar cells of systemic Tmem16A (Tmem16A Cl(-) channel) null mice, but salivation was not assessed in fully developed glands because Tmem16A null mice die within a few days after birth. To test the role of Tmem16A in adult salivary glands, we generated conditional knockout mice lacking Tmem16A in acinar cells (Tmem16A(-/-)). Ca(2+)-dependent salivation was abolished in Tmem16A(-/-) mice, demonstrating that Tmem16A is obligatory for Ca(2+)-mediated fluid secretion. However, the amount of saliva secreted by Tmem16A(-/-) mice in response to the β-adrenergic receptor agonist isoproterenol (IPR) was comparable to that seen in controls, indicating that Tmem16A does not significantly contribute to cAMP-induced secretion. Furthermore, IPR-stimulated secretion was unaffected in mice lacking Cftr (Cftr(∆F508/∆F508)) or ClC-2 (Clcn2(-/-)) Cl(-) channels. The time course for activation of IPR-stimulated fluid secretion closely correlated with that of the IPR-induced cell volume increase, suggesting that acinar swelling may activate a volume-sensitive Cl(-) channel. Indeed, Cl(-) channel blockers abolished fluid secretion, indicating that Cl(-) channel activity is critical for IPR-stimulated secretion. These data suggest that β-adrenergic-induced, cAMP-dependent fluid secretion involves a volume-regulated anion channel. In summary, our results using acinar-specific Tmem16A(-/-) mice identify Tmem16A as the Cl(-) channel essential for muscarinic, Ca(2+)-dependent fluid secretion in adult mouse salivary glands.
顶端钙激活氯离子通道（CaCC）的激活会触发唾液分泌。先前的研究表明，全身性Tmem16A（Tmem16A氯离子通道）基因敲除小鼠的腺泡细胞中不存在CaCC介导的氯离子电流和氯离子外流，但由于Tmem16A基因敲除小鼠在出生后几天内死亡，因此未对完全发育的腺体中的唾液分泌进行评估。为了测试Tmem16A在成年唾液腺中的作用，我们构建了腺泡细胞中缺乏Tmem16A的条件性基因敲除小鼠（Tmem16A-/-）。Tmem16A-/-小鼠中钙依赖性唾液分泌被消除，表明Tmem16A是钙介导的液体分泌所必需的。然而，Tmem16A-/-小鼠对β-肾上腺素能受体激动剂异丙肾上腺素（IPR）产生的唾液分泌量与对照组相当，这表明Tmem16A对cAMP诱导的分泌没有显著贡献。此外，在缺乏Cftr（Cftr∆F508/∆F508）或ClC-2（Clcn2-/-）氯离子通道的小鼠中，IPR刺激的分泌不受影响。IPR刺激的液体分泌激活的时间进程与IPR诱导的细胞体积增加的时间进程密切相关，这表明腺泡肿胀可能激活了一个体积敏感的氯离子通道。事实上，氯离子通道阻滞剂消除了液体分泌，表明氯离子通道活性对IPR刺激的分泌至关重要。这些数据表明，β-肾上腺素能诱导的、cAMP依赖性的液体分泌涉及一个体积调节的阴离子通道。总之，我们使用腺泡特异性Tmem16A-/-小鼠的研究结果表明，Tmem16A是成年小鼠唾液腺中对于毒蕈碱、钙依赖性液体分泌必不可少的氯离子通道。
