We are investigating transduction mechanisms in a major peripheral chemosensory organ, the rat carotid body, using short- and long-term dissociated cell cultures and patch-clamp, whole-cell recording. In this study membrane properties of cultured glomus or type I cells were characterized with conventional whole-cell recording and the new perforated-patch technique during control (160 Torr) and low-PO2 (20 Torr) conditions. These cells contained voltage-gated channels typical of electrically excitable cells and had large input resistances (approx. 2 G omega). Under whole-cell voltage clamp the cells produced brief inactivating inward currents, which were largely abolished by 0.2-2.0 microM tetrodotoxin, followed by prolonged outward currents, which were reduced by 5 mM tetraethylammonium or abolished by the substitution of Cs+ ions for K+ ions in the pipette. On exposure to hypoxia the outward K+ current was reduced typically by 15%-20% with both conventional whole-cell and perforated-patch recording, which minimizes washout of the cell's cytoplasm. This effect persisted in long-term culture and was specific, since the inward current was unaffected and, moreover, it did not occur in cultured small intensely fluorescent cells, which are closely related to glomus cells. These properties of cultured rat glomus cells are contrasted with those recently reported for freshly isolated rabbit glomus cells.