Heterogeneity of neuronal nicotinic acetylcholine receptors in 5-HT-containing chemoreceptor cells of the chicken aorta.

The effects of nicotinic agonists and antagonists on whole-cell currents and 5-hydroxytryptamine (5-HT) release were studied in order to characterize nicotinic ACh receptors on the 5-HT-containing chemoreceptor cells of the chicken aorta. ACh, nicotine and dimethylphenylpiperazinium (DMPP) evoked concentration-dependent inward currents accompanied by increases in current noise at a holding potential of -70 mV. The peak amplitude of the current response to DMPP was 50% larger than that to either nicotine or ACH: Hexamethonium, alpha - bungarotoxin (alpha - BTX) and methyllycaconitine decreased nicotine-induced inward currents in a concentration-dependent manner. Although hexamethonium (0.1 mM) abolished the current response to nicotine (30 microM), a high concentration (1 microM) of alpha - BTX decreased it only by about 30% of the control response. Methyllycaconitine (0.1 microM) decreased the current response to nicotine to the same extent as did alpha - BTX whilst a high concentration (10 microM) abolished the response. ACh, nicotine and DMPP caused concentration-dependent increases in 5-HT output from the thoracic aorta which effect was blocked by hexamethonium (0.1 mM). Pre-treatment with alpha - BTX (1 microM) for 30 min reduced the output of 5-HT induced by ACh to 70% of the control response. It is suggested that neuronal nicotinic ACh receptors, sensitive and insensitive to alpha - BTX, are present on the chemoreceptor cells of the chicken aorta, the activation of which causes the release of 5-HT.