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

Abstract

1. 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. 2. 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. 3. Hexamethonium, α-bungarotoxin (α-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 μM), a high concentration (1 μM) of α-BTX decreased it only by about 30% of the control response. Methyllycaconitine (0.1 μM) decreased the current response to nicotine to the same extent as did α-BTX whilst a high concentration (10 μM) abolished the response. 4 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 α-BTX (1 μM) for 30 min reduced the output of 5-HT induced by ACh to 70% of the control response. 5 It is suggested that neuronal nicotinic ACh receptors, sensitive and insensitive to α-BTX, are present on the chemoreceptor cells of the chicken aorta, the activation of which causes the release of 5-HT.