Dissociation of hypoxia-induced chemosensory responses and catecholamine efflux in cat carotid body superfused in vitro

Abstract

1. To examine the correlation between chemosensory response and dopamine release induced by hypoxic stimulation, we studied carotid bodies excised from anaesthetized cats. 2. The carotid bodies with their carotid (sinus) nerves were superfused in vitro with modified Tyrode solution (pH 7.40, at 37.5°C) equilibrated with 20 or 100% O2. The PO2 of the superfusing channel was monitored polarographically. The frequency of chemosensory discharges (f(x)) was recorded from the whole carotid nerve. Catecholamine (CA) efflux mostly consisting of dopamine - was measured by high-speed chronoamperometry through Nafion-coated carbon electrodes placed on the carotid body tissue. Chemosensory stimulation was induced by intrastream injections of NaCN, by superfusion with 100% N2-equilibrated saline (lowering P(O2) to 25-40 Torr) or by flow interruption. 3. Low doses of NaCN increased f(x), but had no measurable effect on CA efflux, while larger doses produced fast increases in f(x), preceding delayed