N-n-alkylpyridinium analogs, a novel class of nicotinic receptor antagonists: selective inhibition of nicotine-evoked [3H] dopamine overflow from superfused rat striatal slices.
Structural simplification of N-n-alkylnicotinium analogs, antagonists at neuronal nicotinic acetylcholine receptors (nAChRs), was achieved by removal of the N-methylpyrrolidino moiety affording N-n-alkylpyridinium analogs with carbon chain lengths of C1 to C20. N-n-Alkylpyridinium analog inhibition of [3H]nicotine and [3H]methyllycaconitine binding to rat brain membranes assessed interaction with alpha4beta2* and alpha7* nAChRs, respectively, whereas inhibition of nicotine-evoked 3H overflow from [3H]dopamine ([3H]DA)-preloaded rat striatal slices assessed antagonist action at nAChR subtypes mediating nicotine-evoked DA release. No inhibition of [3H]methyllycaconitine binding was observed, although N-n-alkylpyridinium analogs had low affinity for [3H]nicotine binding sites, i.e., 1 to 3 orders of magnitude lower than that of the respective N-n-alkylnicotinium analogs. These results indicate that the N-methylpyrrolidino moiety in the N-n-alkylnicotinium analogs is a structural requirement for potent inhibition of alpha4beta2* nAChRs. Importantly, N-n-alkylpyridinium analogs with n-alkyl chains < C10 did not inhibit nicotine-evoked [3H]DA overflow, whereas analogs with n-alkyl chains ranging from C10 to C20 potently and completely inhibited nicotine-evoked [3H]DA overflow (IC50 = 0.12-0.49 microM), with the exceptions of N-n-pentadecylpyridinium bromide (C15) and N-n-eicosylpyridinium bromide (C20), which exhibited maximal inhibition of approximately 50%. The mechanism of inhibition of a representative analog of this structural series, N-n-dodecylpyridinium iodide, was determined by Schild analysis. Linear Schild regression with slope not different from unity indicated competitive antagonism at nAChRs mediating nicotine-evoked [3H]DA overflow and a KB value of 0.17 microM. Thus, the simplified N-n-alkylpyridinium analogs are potent, selective, and competitive antagonists of nAChRs mediating nicotine-evoked [3H]DA overflow, indicating that the N-methylpyrrolidino moiety is not a structural requirement for interaction with nAChR subtypes mediating nicotine-evoked DA release.
Grinevich
Vladimir P
VP
College of Pharmacy, University of Kentucky, Lexington, KY 40536-0082, USA.
Crooks
Peter A
PA
Sumithran
Sangeetha P
SP
Haubner
Aaron J
AJ
Ayers
Joshua T
JT
Dwoskin
Linda P
LP
D000157:Aconitine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000166:cytology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D066298:In Vitro Techniques; D009538:Nicotine / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology*; D011726:Pyridinium Compounds / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014316:Tritium
D018733:Nicotinic Antagonists; D011726:Pyridinium Compounds; D011978:Receptors, Nicotinic; D014316:Tritium; C001524:Laurosept; C054634:methyllycaconitine; D009538:Nicotine; D004298:Dopamine; D000157:Aconitine