Abstract

We studied the effects of nicotine, acetylcholine (ACh) and dopamine (DA) on the frequency of chemosensory discharges (f(x)) and catecholamine (CA) efflux in the cat carotid body superfused in vitro. CA efflux was measured by changes in CA concentration (Delta CA) determined by chronoamperometry with nafionated carbon-fiber microelectrodes inserted in the carotid body, while f(x) was recorded simultaneously from the carotid (sinus) nerve. Nicotine (10-20 mu g) and ACh (>100 mu g) increased f(x) in all carotid bodies (n = 16), but produced a delayed Delta CA (similar to 0.65 mu M) in only half of them. Eserine potentiated ACh-evoked increases in f(x) and CA effluxes. Nicotine and ACh-induced Delta CA were rapidly reduced upon repeated administration. While f(x) increases evoked by low doses of nicotine or ACh were reduced or abolished by prior administration of exogenous DA (>100 mu g). CA effluxes were enhanced and hastened. Thus, cholinergic-induced changes in f(x) are dissociated from CA efflux. (C) 2000 Elsevier Science B.V. All rights reserved.