Immunohistochemical Identification of K⁺ Channel Subunits in Neurons from Chemosensitive Regions of Rat Brainstem

CO ₂ -sensitive neurons control breathing and are found in various regions of the brainstem. Neurons within these areas respond to CO ₂ with different percentages and different magnitudes of changes in firing rate responses to CO ₂ . We propose that neuronal responses to CO ₂ are different because of differences in the ion channels expressed on neurons in these regions. The current study localized pH-sensitive K ⁺ channels in two different areas of the brainstem, the solitary tract (SC) (nucleus tractus solitarius, NTS, and dorsal motor nucleus, DMN) and locus coeruleus (LC). Brainstem slices (300µm) were fixed and thin sectioned (20-40µm). Nissl staining was used to stain all cells and glial fibrillary acidic protein (GFAP)stained astrocytes. Neurons were identified as Nissl positive/GFAP negative. Sections were stained with antibodies for pH-sensitive subunits of voltage-sensitive (Kv1.4) and inwardly-rectifying (Kir2.3 and Kir4.1) K ⁺ channels. We found that Kv1.4 was prevalent on SC neurons (60-90%), which stained less for Kir2.3 and 4.1 (30-40%). In contrast, LC neurons stained similarly (50-60%) for Kv1.4, Kir2.3 and Kir4.1. These data are consistent with an A current (inhibitable by 4 aminopyridine) playing a major role in the CO ₂ response of SC neurons but both an A current and Kir channels playing a role in the CO ₂ response of LC neurons.

Supported by NIH R01 HL56683 (RWP) and T35 HL007805 (CM).