Inward rectifier K+ channels play important roles in controlling the excitability of neuronal cells, and in regulating the local extracellular K+ concentration in neuronal tissues by glial cells (K+ spatial buffering).
In this study, we studied the expression of Kir2 channel subunits in rat DRG and spinal cord at the level of L4-L5 immunohistochemically. In DRG, the immunoreactivity of Kir2.1, Kir2.2 and Kir2.3 channels was present in almost all neurons. It is of interest that Kir2.3 was clearly expressed in satellite cells surrounding neuronal soma. In the spinal cord, Kir2.1, Kir2.2, and Kir2.3 subunits were all present in the gray matter of dorsal and ventral horn and moderately in the white matter also. Kir2.2 protein level was the highest in these three Kir2 subunits. Throughout the gray matter of the spinal cord, high levels of the Kir2 channel proteins were expressed in the substantia gelatinosa of the dorsal horn. Kir2 immunoreactive neurons and astrocytes were frequently observed in the dorsal horn of lamina I to lamina III and in the lateral spinal nucleus of the dorsolateral funiculus. Interestingly, nuclear immunostaining with anti-Kir2.1 antibody was observed in neurons of the dorsal horn. Kir2.2 immunoreactivity in neurons in lamina I to lamina III and the lateral spinal nucleus was concentrated around the nuclei immunoreactive with NeuN. Some of Kir2.3 immunoreactive neurons showed the immunoreaction within the nucleus. Colocalization of Kir2.1 and 2.3 and that of Kir2.2 and 2.3 were likely present in both neurons and glial cells. Immunoreactive signals other than those in soma of neurons and glial cells seemed to be mainly in nerve fibers or nerve terminals. These immunoreactive products were abundant in lamina I and lamina II. In the ventral horn, most motor neurons were intensely immunoreactive with all three Kir2 subunits. Our study indicates that Kir2 channels may be involved in the generation of receptor potential and the transmission of the signals in the sensory systems.