Abstract

Using a chronoamperometric technique with carbon-fiber microelectrodes and neural recordings, we simultaneously measured the effects of the following procedures on catecholamine efflux (?CA) and frequency of chemosensory discharges (f(x)) from superfused cat carotid body: 1) the addition of CO2-HCO3 - to Tyrode solution previously buffered with N-2- hydroxyethylpiperazine-N' -2-ethane-sulfonic acid, maintaining pH at 7.40; 2) hypercapnia (10% CO2, pH 7.10); 3) hypoxia (PO2 h ? 40 Torr) with and without CO2-HCO3 -; and 4) the impact of several boluses of dopamine (DA; 10-100 ?g) on hypoxic and hypercapnic challenges. With CO2-HCO3 -, hypoxia increased f(x) which preceded ?CA increases, whereas hypercapnia raised f(x) but did not consistently increase ?CA. Repeated stimuli induced similar f(x) increases, but attenuated ?CA. After DA, hypoxia produced larger ?CA, which preceded chemosensory responses. Without CO2-HCO3 -, hypoxia produced a similar pattern of ?CA and f? responses. Switching to Tyrode solution with CO2-HCO3 - at pH 7.40 raised f(x) but did not increase ?CA. With CO2- HCO3 - and after DA, hypoxic-induced ?CAs were larger than in its absence. Results suggest that DA release is not essential for chemosensory excitation.