Extracellular pH changes in the superfused cat carotid body during hypoxia and hypercapnia

Abstract

Extracellular pH changes were measured in the superfused cat carotid body with double barreled pH glass microelectrodes, under constant pH ( 7.45 ± 0.02), temperature (35°C) and flow (3.6 ml/min) of the superfusion medium. Changes of pO 2 in the medium from about 188 Torr (30% O 2) to 35 or 12 Torr (5% and 2% respectively) called hypoxia, induced a change of the pH signal of about 0.1 units indicating acidification of the tissue. Medium pH monitored with pH macroelectrode did not change during hypoxic stimulation. An increase of pCO 2 in the medium from about 20 Torr ( 3%CO 2, pH7.45 ± 0.02 ) to 70 Torr ( 12%CO 2, pH6.98 ± 0.01 ) called hypercapnia, under constant pO 2 ( 188 ± 2Torr), temperature (35°C) and flow (3.6 ml/min) resulted in acidification of the tissue of about 0.3 pH units. Extracellular pH changes during hypoxia did not occur when the superfusion medium had no glucose; however, pH changes during hypercapnia persisted under these conditions. The hypoxic and hypercapnic chemosensory response of the sinus nerve were decreased or abolished during glucose deprivation in a time-dependent manner. Replacement of glucose with 2-deoxyglucose in the medium led to a similar pattern, i.e. inhibition of the hypoxic and hypercapnic chemosensory nerve response and of the extracellular hypoxic pH changes. These results indicate that glycolysis takes place and contributes to O 2 and CO 2-chemoreception in the carotid body.