STIMULUS-SPECIFIC MOBILIZATION OF DOPAMINE AND NOREPINEPHRINE STORES IN CAT CAROTID-BODY

The catecholamines (CAs), dopamine (DA) and norepinephrine (NE), are s ynthesized and stored in carotid body chemosensory type I cells. Previ ous studies in our laboratory demonstrated that low concentrations of nicotine preferentially evoke the release of NE from rabbit type I cel ls, whereas hypoxia mobilizes DA and NE in proportion to their stores in the tissue. The primary objective of the present study was to exami ne whether hypoxia, nicotine and elevated concentrations (30 mM) of K evoke the preferential release of DA vs. NE from cat carotid bodies s uperfused in vitro. In this species, where tissue stores of DA and NE are nearly equal, hypoxia evoked the preferential release of DA from n ormal carotid bodies. This pattern of release evoked by low O-2 was al so present following chronic removal of the superior cervical ganglion , which eliminated NE contained in the sympathetic innervation to the carotid body. In contrast, nicotine and high-K+ preferentially mobiliz ed NE in these sympathectomized animals. Sympathectomy also reduced th e percent of DA (but not NE) content released from type I cells in res ponse to any of the three stimuli. Our findings suggest that chemosens ory type I cells possess stimulus-specific mechanisms for CA mobilizat ion and that the sympathetic innervation modulates the metabolism and release of CAs in the cat carotid body. (C) 1997 Elsevier Science B.V.