Desensitization of nicotine-stimulated [3H]dopamine release from mouse striatal synaptosomes.
Potential desensitization of brain nicotinic receptors was studied using a [3H]dopamine release assay. Nicotine-stimulated [3H]dopamine release from mouse striatal synaptosomes was concentration-dependent with an EC50 of 0.33 +/- 0.13 microM and a Hill coefficient of 1.44 +/- 0.18. Desensitization by activating concentrations of nicotine had a similar EC50 and a half-time of 35 s. Concentrations of nicotine that evoked little release also induced a concentration-dependent desensitization (EC50 = 6.9 +/- 3.6 nM, t1/2 = 1.6-2.0 min, nH = 1.02 +/- 0.01). Both types of desensitization produced a maximum 75% decrease in [3H]dopamine release. Recovery from desensitization after exposure to low or activating concentrations of nicotine was time-dependent with half-times of 6.1 min and 12.4 min, respectively. Constants determined for binding of [3H]nicotine to striatal membrane at 22 degrees C included a KD of 3.7 +/- 0.5 nM, Bmax of 67.5 +/- 2.2 fmol/mg, and Hill coefficient of 1.07 +/- 0.06. Association of nicotine with membrane binding sites was biphasic with half-times of 9 s and 1.8 min. The fast rate process contributed 37% of the total reaction. Dissociation was a uniphasic process with a half-time of 1.6 min. Comparison of constants determined by the release and binding assays indicated that the [3H]-nicotine binding site could be the presynaptic receptor involved in [3H]dopamine release in mouse striatal synaptosomes.
Grady
S R
SR
Institute for Behavioral Genetics, University of Colorado, Boulder.
Marks
M J
MJ
Collins
A C
AC
D000818:Animals; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D005260:Female; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D009538:Nicotine / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000502:physiology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D014316:Tritium
D011978:Receptors, Nicotinic; D014316:Tritium; D009538:Nicotine; D004298:Dopamine