DOPAMINE INCREASES IN CAT CAROTID-BODY DURING EXCITATION BY CARBON-MONOXIDE - IMPLICATIONS FOR A CHROMOPHORE THEORY OF CHEMORECEPTION

Studies of dopamine (DA) release were conducted with 10 perfused/super fused cat carotid bodies using shallow recessed Nafion polymer-coated microsensors (tips similar to 5 mu m). Simultaneous measurements of ti ssue DA and neuronal discharge (ND) from the sinus nerve were made aft er switching from normoxic, normocapnic control perfusate (20% O-2, 5% CO2, balance N-2) to a normoxic, normocapnic perfusate equilibrated w ith a high tension (> 550 Torr) of carbon monoxide (CO). When high P-C O perfusate was delivered in the dark, ND increased from a baseline of 89 +/- 24 (SE) impulses/s, to a peak excitation of 374 +/- 44 impulse s/s within 15-30 s. Excitation then diminished to a plateau of 281 +/- 36 impulses/s within 1-2 min. Both peak and plateau ND were significa ntly above baseline (P < 0.05). Average tissue DA values increased abo ve basal levels by + 7.2 +/- 1.0 and + 5.6 +/- 0.6 mu M, respectively during the peak and plateau Nn phases (P < 0.05). Bright light restore d the chemosensory activity to baseline, but had no effect on DA. Both chemosensory excitation and tissue DA responses to high CO in the dar k were diminished in 3 carotid bodies perfused with Ca2+-free solution s. Responses were reduced even further with Ca2+ chelator (EGTA) in th e perfusate. The results suggest that the effect of high P-CO on DA re lease and chemosensory excitation are dependent on Ca2+ in the media, but the two events are not coupled. (C) 1997 Elsevier Science B.V.