To test the hypothesis that hypoxia may induce cellular acidification during chemotransduction in the carotid body, we compared the effects of hypoxia and of extracellular acidosis on intracellular pH (pHi) of glomus cells cultured from rat and cat carotid bodies. The cells were prepared and cultured for 2-7 days. The plated cells were loaded with a pH-sensitive fluorescent probe, SNARF-1-acetoxymethyl ester, and were placed in a closed chamber and superfused. The effects of lowering PO2 and pH in the superfusion medium containing CO2-HCO3- buffer on the glomus cell pHi were measured at 37 degrees C. The pHi was measured in a single or a few isolated cells with single excitation at 540 nm and dual emission at 590 and 640 nm, after the exposure to different PO2 levels from 132 to 43, 14, and 1-2 Torr for 10-12 min in the closed chamber. The resting pHi values were 7.263 +/- 0.008 for rat and 7.175 +/- 0.004 for cat carotid body glomus cells. For a decrease of PO2 from 132 Torr to 14 Torr, the change in pHi values, on average, for cat and rat glomus cells was 0.034 lower, and with PO2 decrease to 1-2 Torr for the cat glomus cells, the change in pHi values was 0.051 lower. On the other hand, when the perfusate pH values were decreased from 7.4 to 6.9 during normoxia, the reduction of change in pHi values were 0.327 for the rat and 0.397 for the cat. Thus glomus cell pHi change due to low PO2 exposure was not significant and was not commensurate with the large increases in the chemosensory activity.