Effects of CO2-HCO3 2 on catecholamine efflux from cat carotid body

Iturriaga, Rodrigo, and Julio Alcayaga. Effects of CO2HCO3 2 on catecholamine efflux from cat carotid body. J. Appl. Physiol. 84(1): 60–68, 1998.—Using a chronoamperometric technique with carbon-fiber microelectrodes and neural recordings, we simultaneously measured the effects of the following procedures on catecholamine efflux (DCA) and frequency of chemosensory discharges (fx) from superfused cat carotid body: 1) the addition of CO2-HCO3 2 to Tyrode solution previously buffered with N-2-hydroxyethylpiperazine-N8 -2-ethanesulfonic 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 μg) on hypoxic and hypercapnic challenges. With CO2-HCO3 , hypoxia increased fx which preceded DCA increases, whereas hypercapnia raised fx but did not consistently increase DCA. Repeated stimuli induced similar fx increases, but attenuated DCA. After DA, hypoxia produced larger DCA, which preceded chemosensory responses. Without CO2-HCO3 , hypoxia produced a similar pattern of DCA and fx responses. Switching to Tyrode solution with CO2HCO3 2 at pH 7.40 raised fx but did not increase DCA. With CO2-HCO3 2 and after DA, hypoxic-induced DCAs were larger than in its absence. Results suggest that DA release is not essential for chemosensory excitation.