Leffler Andreas, Linte Ramona Madalina, Nau Carla, Reeh Peter, Babes Alexandru
Department of Anaesthesiology, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany.
Eur J Neurosci. 2007 Jul;26(1):12-22. doi: 10.1111/j.1460-9568.2007.05643.x. Epub 2007 Jun 26.
Heat-activated ion channels from the vanilloid-type TRP group (TRPV1-4) seem to be central for heat-sensitivity of nociceptive sensory neurons. Displaying a high-threshold (> 52 degrees C) for activation, TRPV2 was proposed to act as a sensor for intense noxious heat in mammalian sensory neurons. However, although TRPV2 is expressed in a distinct population of thinly myelinated primary afferents, a widespread expression in a variety of neuronal and non-neuronal tissues suggests a more diverse physiological role of TRPV2. In its role as a heat-sensor, TRPV2 has not been thoroughly characterized in terms of biophysical and pharmacological properties. In the present study, we demonstrate that the features of heterologously expressed rat TRPV2 closely resemble those of high-threshold heat-evoked currents in medium- and large-sized capsaicin-insensitive rat dorsal root ganglion (DRG) neurons. Both in TRPV2-expressing human embryonic kidney (HEK)293t cells and in DRGs, high-threshold heat-currents were sensitized by repeated activation and by the TRPV1-3 agonist, 2-aminoethoxydiphenyl borate (2-APB). In addition to a previously described block by ruthenium red, we identified the trivalent cations, lanthanum (La(3+)) and gadolinium (Gd(3+)) as potent blockers of TRPV2. Thus, we present a new pharmacological tool to distinguish between heat responses of TRPV2 and the closely related capsaicin-receptor, TRPV1, which is strongly sensitized by trivalent cations. We demonstrate that self-sensitization of heat-evoked currents through TRPV2 does not require extracellular calcium and that TRPV2 can be activated in cell-free membrane patches in the outside-out configuration. Taken together our results provide new evidence for a role of TRPV2 in mediating high-threshold heat responses in a subpopulation of mammalian sensory neurons.
来自香草酸型瞬时受体电位（TRP）家族（TRPV1 - 4）的热激活离子通道似乎是伤害性感觉神经元热敏感性的核心。TRPV2激活阈值较高（> 52摄氏度），被认为是哺乳动物感觉神经元中强烈有害热的感受器。然而，尽管TRPV2在一群特定的薄髓鞘初级传入神经元中表达，但它在多种神经元和非神经元组织中的广泛表达表明其生理作用更为多样。作为热感受器，TRPV2在生物物理和药理学特性方面尚未得到充分表征。在本研究中，我们证明异源表达的大鼠TRPV2的特性与中大型辣椒素不敏感的大鼠背根神经节（DRG）神经元中高阈值热诱发电流的特性非常相似。在表达TRPV2的人胚肾（HEK）293t细胞和DRG中，高阈值热电流都可通过重复激活以及TRPV1 - 3激动剂2 - 氨基乙氧基二苯硼酸（2 - APB）而致敏。除了先前描述的钌红阻断作用外，我们还确定三价阳离子镧（La(3+)）和钆（Gd(3+)）是TRPV2的有效阻滞剂。因此，我们提供了一种新的药理学工具，用于区分TRPV2与密切相关的辣椒素受体TRPV1的热反应，TRPV1会被三价阳离子强烈致敏。我们证明通过TRPV2的热诱发电流的自身致敏不需要细胞外钙，并且TRPV2可以在膜片外翻式的无细胞膜片中被激活。综合我们的结果为TRPV2在介导哺乳动物感觉神经元亚群中的高阈值热反应方面的作用提供了新的证据。
