Shibukawa Yoshiyuki, Sato Masaki, Kimura Maki, Sobhan Ubaidus, Shimada Miyuki, Nishiyama Akihiro, Kawaguchi Aya, Soya Manabu, Kuroda Hidetaka, Katakura Akira, Ichinohe Tatsuya, Tazaki Masakazu
Department of Physiology, Tokyo Dental College, Tokyo, 101-0061, Japan,
Pflugers Arch. 2015 Apr;467(4):843-63. doi: 10.1007/s00424-014-1551-x. Epub 2014 Jun 18.
Various stimuli induce pain when applied to the surface of exposed dentin. However, the mechanisms underlying dentinal pain remain unclear. We investigated intercellular signal transduction between odontoblasts and trigeminal ganglion (TG) neurons following direct mechanical stimulation of odontoblasts. Mechanical stimulation of single odontoblasts increased the intracellular free calcium concentration ([Ca(2+)]i) by activating the mechanosensitive-transient receptor potential (TRP) channels TRPV1, TRPV2, TRPV4, and TRPA1, but not TRPM8 channels. In cocultures of odontoblasts and TG neurons, increases in [Ca(2+)]i were observed not only in mechanically stimulated odontoblasts, but also in neighboring odontoblasts and TG neurons. These increases in [Ca(2+)]i were abolished in the absence of extracellular Ca(2+) and in the presence of mechanosensitive TRP channel antagonists. A pannexin-1 (ATP-permeable channel) inhibitor and ATP-degrading enzyme abolished the increases in [Ca(2+)]i in neighboring odontoblasts and TG neurons, but not in the stimulated odontoblasts. G-protein-coupled P2Y nucleotide receptor antagonists also inhibited the increases in [Ca(2+)]i. An ionotropic ATP (P2X3) receptor antagonist inhibited the increase in [Ca(2+)]i in neighboring TG neurons, but not in stimulated or neighboring odontoblasts. During mechanical stimulation of single odontoblasts, a connexin-43 blocker did not have any effects on the [Ca(2+)]i responses observed in any of the cells. These results indicate that ATP, released from mechanically stimulated odontoblasts via pannexin-1 in response to TRP channel activation, transmits a signal to P2X3 receptors on TG neurons. We suggest that odontoblasts are sensory receptor cells and that ATP released from odontoblasts functions as a neurotransmitter in the sensory transduction sequence for dentinal pain.
当各种刺激施加于暴露的牙本质表面时会引发疼痛。然而，牙本质疼痛的潜在机制仍不清楚。我们研究了在对成牙本质细胞进行直接机械刺激后，成牙本质细胞与三叉神经节（TG）神经元之间的细胞间信号转导。对单个成牙本质细胞进行机械刺激通过激活机械敏感瞬时受体电位（TRP）通道TRPV1、TRPV2、TRPV4和TRPA1增加细胞内游离钙浓度（[Ca(2+)]i），但不激活TRPM8通道。在成牙本质细胞与TG神经元的共培养物中，不仅在受到机械刺激的成牙本质细胞中观察到[Ca(2+)]i增加，在相邻的成牙本质细胞和TG神经元中也观察到了增加。在没有细胞外Ca(2+)以及存在机械敏感TRP通道拮抗剂的情况下，这些[Ca(2+)]i的增加被消除。泛连接蛋白-1（ATP可渗透通道）抑制剂和ATP降解酶消除了相邻成牙本质细胞和TG神经元中[Ca(2+)]i的增加，但在受刺激的成牙本质细胞中没有消除。G蛋白偶联P2Y核苷酸受体拮抗剂也抑制了[Ca(2+)]i的增加。离子型ATP（P2X3）受体拮抗剂抑制了相邻TG神经元中[Ca(2+)]i的增加，但在受刺激的或相邻的成牙本质细胞中没有抑制作用。在对单个成牙本质细胞进行机械刺激期间，连接蛋白-43阻滞剂对在任何细胞中观察到的[Ca(2+)]i反应没有任何影响。这些结果表明，响应TRP通道激活，通过泛连接蛋白-1从受机械刺激的成牙本质细胞释放的ATP将信号传递给TG神经元上的P2X3受体。我们认为成牙本质细胞是感觉受体细胞，并且从成牙本质细胞释放的ATP在牙本质疼痛的感觉转导序列中作为神经递质发挥作用。
