Ion channels and their functions at the node of Ranvier of mammalian somatosensory afferent fibers

Ranvier淋巴结是感觉神经、运动神经和神经的髓鞘神经纤维上高度特化的轴突区域

Nodes of Ranvier are highly specialized axonal regions on myelinated nerve fibers of sensory, motor and central nervous systems where action potentials are propagated by saltatory (leap in Latin word) conduction. Saltatory conduction through nodes of Ranvier ensures timely sensory and motor responses and precise signal processing in the CNS. A number of neurological diseases affect nodes of Ranvier to impair saltatory conduction leading to motor disorders, such as paralysis and sensory dysfunctions, such as pain, numbness, and other abnormal sensations. Knowledge of ion channels and their functions at mammalian nodes of Ranvier is a key to fully understanding saltatory conduction under both physiological and pathological conditions, and for potential treatments of those sensory and motor disorders. The overall goal of this project is to study ion channel mechanisms for securing saltatory conduction of action potentials at mammalian nodes of Ranvier. We have recently developed the in situ patch-clamp recording technique for nodes of Ranvier in somatosensory afferent fibers of rats. In the preliminary studies we have found that nodes of Ranvier express surprisingly high levels of the two-pore domain potassium channels (K2P channels), a unique family of ion channels that constitutively open, and the function of which, in action potentials, as well as in nerve conduction was previously unknown. Functionally, our preliminary studies strongly suggest that K2P channels are key molecules for securing saltatory conduction in myelinated somatosensory afferent fibers of mammals. In this application, we will use the in situ patch-clamp recording technique in conjunction with pharmacology, gene knockdown, and immunochemistry approaches to achieve the following specific aims. Aim 1. Characterize K2P channels and elucidate their molecular identities at the node of Ranvier of rat somatosensory afferent fibers. In this aim we will pin down K2P channel subtypes at the node of Ranvier and profile their pharmacological and single channel properties. Aim 2. Study specific roles of K2P channels in securing saltatory conduction at the node of Ranvier of rat somatosensory afferent fibers. This aim will elucidate that the K2P channels at the node of Ranvier play a key role in rapid action potential repolarization and in securing high speed and high frequency saltatory conduction. Aim 3. Elucidate that K2P channels at the node of Ranvier play a key role in temperature-dependent saltatory conduction on rat somatosensory afferent fibers. This aim will test the idea that K2P channels at the node of Ranvier are highly thermal sensitive, which is a determinant factor controlling the velocity and fidelity of saltatory conduction at different temperatures. This aim exemplifies that biological factors affecting K2P channel activity will highly impact saltatory conductions in myelinated nerve fibers. Completion of the 3 Aims will elucidate a novel ion channel mechanism that secures saltatory conduction, which may have implications in sensory and motor disorders with impaired saltatory conduction at the node of Ranvier.