DOPAMINE, SENSORY DISCHARGE, AND STIMULUS INTERACTION WITH CO2 AND O-2 IN CAT CAROTID-BODY

It is hypothesized that carotid body chemosensory activity is coupled to neurosecretion. The purpose of this study was to examine whether th ere was a correspondence between carotid body tissue dopamine (DA) lev els and neuronal discharge (ND) measured from the carotid sinus nerve of perfused cat carotid bodies and to characterize interaction between CO2 and O-2 in these responses. ND and tissue DA were measured after changing from normoxic, normocapnic control bicarbonate buffer (PO2 >1 20 Torr, PCO2 25-30 Torr, pH similar to 7.4) to normoxic hypercapnia ( PCO2 55-57 Torr, pH 7.1-7.2) or to hypoxic solutions (PO2 30-35 Torr) with normocapnia (PCO2 25-30 Torr, pH similar to 7.4) or hypocapnia (P CO2 10-15 Torr, pH 7.6-7.8). Similar temporal changes for ND and tissu e DA were found for all of the stimuli, although there was a much diff erent proportional relationship for normoxic hypercapnia. Both ND and DA increased above baseline values during flow interruption and normoc apnic hypoxia, and both decreased below baseline values during hypoxic hypocapnia. In contrast, normoxic hypercapnia caused an initial incre ase in ND, from a baseline of 175 +/- 12 (SE) to a peak of 593 +/- 20 impulses/s within 4.6 +/- 0.9 s, followed by adaptation, whereas ND de clined to 423 +/- 20 impulses/s after 1 min. Tissue DA initially incre ased from a baseline of 17.9 +/- 1.2 mu M to a peak of 23.2 +/- 1.2 mu M within 3.0 +/- 0.7 s, then declined to 2.6 +/- 1.0 mu M. The substa ntial decrease in tissue DA during normoxic hypercapnia was not consis tent with the parallel changes in DA with ND that were observed for hy poxic stimuli.