As there are wide inter-species variations in the molecular nature of the O2 sensitive Kv channels in arterial chemoreceptor, we have characterized the expression of these channels and their hypoxic sensitivity in the mouse carotid body (CB). CB chemoreceptor cells were obtained from a transgenic mouse expressing GFP under the control of tyrosine hydroxylase (TH) promoter. Immunocytochemical identification of TH in CB cell cultures reveals a good match with GFP positive cells. Furthermore, these cells show an increase in [Ca2+]i in response to low pO2, demonstrating their ability to engender a physiological response. Whole-cell experiments demonstrated slow-inactivating K+ currents with activation threshold around -30 mV and a bi-exponential kinetic of deactivation (t of 6.24± 0.52 and 32.85± 4.14 ms). TEA sensitivity of the currents identified also two different components (IC50 of 17.8± 2,8 and 940.0± 14.7 µM). Current amplitude decreased reversibly in response to hypoxia, which selectively affected the fast deactivating component. Hypoxic inhibition was also abolished in the presence of low (10-50 µM) concentrations of TEA, suggesting that O2 interacts with the component of the current most sensitive to TEA. The kinetic and pharmacological profile of the currents suggested the presence of Kv2 and Kv3 channels as their molecular correlates, and we have identified several members of these two subfamilies by single-cell PCR and immunocytochemistry. This report represent the first functional and molecular characterization of Kv channels in mouse CB chemoreceptor cells, and strongly suggest that O2-sensitive Kv channels in this preparation belong to the Kv3 subfamily.