title: Two distinct (-)nicotine binding sites in goldfish brain. Identification and characterization of putative neuronal nicotinic acetylcholine receptor subtypes.
abstract: The binding of (-)-[3H]nicotine to membrane fragments and a detergent solubilized fraction of goldfish brain was characterized. (-)-[3H]nicotine binding was not displaced by alpha-bungarotoxin, but was displaced by (-)nicotine and carbamoylcholine with Ki of approximately 8.6 and 86 nM, respectively. Preincubation of solubilized membrane extract with alpha-bungarotoxin-coupled Sepharose resulted in the loss of approximately 50% of the (-)-[3H]nicotine binding protein from the eluent and an increase in (-)-[3H]nicotine binding to the gel compared to control, non-alpha-bungarotoxin Sepharose. 125I-alpha-bungarotoxin binding protein in the eluent from the same preincubation experiments was totally removed. In addition, incubation of the solubilized tissue extracts with alpha-bungarotoxin-coupled Sepharose resulted in an increase in the affinity for (-)-[3H]nicotine in the eluent (mean KD = 3.1) compared to control solubilized tissue extracts (KD = 6.4 nM). Specific (-)-[3H]nicotine binding sites could be eluted from the alpha-bungarotoxin-coupled Sepharose with carbamoylcholine and D-tubocurarine. Similar to previously reported 125I-alpha-bungarotoxin binding data, eye removal resulted in an approximately 40% decrease in (-)-[3H]nicotine binding in the contralateral tectum compared to that in the ipsilateral tectum. These data indicate that at least two distinct subtypes of (-)nicotine binding sites may be present in goldfish brain, one which binds alpha-bungarotoxin and (-)nicotine and another which binds only (-)nicotine.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002038:Bungarotoxins / Q000378:metabolism; D006054:Goldfish; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D009538:Nicotine / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013237:Stereoisomerism
chemical_list: D002038:Bungarotoxins; D011978:Receptors, Nicotinic; D009538:Nicotine