Neuronal and glial expression of inward rectifier potassium channel subunits Kir2.x in rat dorsal root ganglion and spinal cord

Inward rectifier K+ channels of the Kir2.x subfamily play important roles in controlling the neuronal excitability. Although their cellular localization in the brain has been extensively studied, only a few studies have examined their expression in the spinal cord and peripheral nervous system. In this study, immunohistochemical analyses of Kir2.1, Kir2.2, and Kir2.3 expression were performed in rat dorsal root ganglion (DRG) and spinal cord using bright-field and confocal microscopy. In DRG, most ganglionic neurons expressed Kir2.1, Kir2.2 and Kir2.3, whereas satellite glial cells chiefly expressed Kir2.3. In the spinal cord, Kir2.1, Kir2.2 and Kir2.3 were all expressed highly in the gray matter of dorsal and ventral horns and moderately in the white matter also. Within the gray matter, the expression was especially high in the substantia gelatinosa (lamina II). Confocal images obtained using markers for neuronal cells, NeuN, and astrocytes, Sox9, showed expression of all three Kir2 subunits in both neuronal somata and astrocytes in lamina I-III of the dorsal horn and the lateral spinal nucleus of the dorsolateral funiculus. Immunoreactive signals other than those in neuronal and glial somata were abundant in lamina I and II, which probably located mainly in nerve fibers or nerve terminals. Colocalization of Kir2.1 and 2.3 and that of Kir2.2 and 2.3 were present in neuronal and glial somata. In the ventral horn, motor neurons and interneurons were also immunoreactive with the three Kir2 subunits. Our study suggests that Kir2 channels composed of Kir2.1-2.3 subunits are expressed in neuronal and glial cells in the DRG and spinal cord, contributing to sensory transduction and motor control.