Astrocyte heterogeneity is an emerging concept in which astrocytes within or between brain regions show variable morphological and/or gene expression profiles that presumably reflect different functional roles. Recent evidence indicates that retrotrapezoid nucleus (RTN) astrocytes sense changes in tissue CO2/H+ to regulate respiratory activity; however, mechanism(s) by which they do so remain unclear. Alterations in inward K+ currents represent a potential mechanism by which CO2/H+ signals may be conveyed to neurons. Here, we use slice electrophysiology in rats of either sex to show that RTN astrocytes intrinsically respond to CO2/H+ by inhibition of an inward rectifying potassium (Kir) conductance and depolarization of the membrane, while cortical astrocytes do not exhibit such CO2/H+-sensitive properties. Application of Ba2+ mimics the effect of CO2/H+ on RTN astrocytes as measured by reductions in astrocyte Kir-like currents and increased RTN neuronal firing. These CO2/H+-sensitive currents increase developmentally, in parallel to an increased expression in Kir4.1 and Kir5.1 in the brainstem. Finally, the involvement of Kir5.1 in the CO2/H+-sensitive current was verified using a Kir5.1 KO rat. These data suggest that Kir inhibition by CO2/H+ may govern the degree to which astrocytes mediate downstream chemoreceptive signaling events through cell-autonomous mechanisms. These results identify Kir channels as potentially important regional CO2/H+ sensors early in development, thus expanding our understanding of how astrocyte heterogeneity may uniquely support specific neural circuits and behaviors.