Long-lasting inactivation of nicotinic receptor function in vitro by treatment with high concentrations of nicotine

Exposure of nicotinic acetylcholine receptors (nAChRs) to brief pulses of nicotine results in the stimulation of dopamine release, whereas prolonged treatment with low concentrations of nicotine (approximate to 10 nM) produces a reversible blockade of a subsequent nicotine challenge as a result of nAChR desensitization. We and others have observed that, following prolonged treatment with stimulating (mu M) concentrations of nicotine, there is incomplete recovery from desensitization. In this study we investigated this nonrecoverable component by characterizing the ability of nicotine to stimulate [H-3]dopamine release from rat striatal synaptosomes following recovery from nicotine-induced desensitization. Brief (12 s) exposure to 30 mu M nicotine, or longer exposure (greater than or equal to 5 min) to 0.3 mu M nicotine produced a long-lasting decrease in nAChR function with an apparent IC50 of 0.7 mu M. The maximal inactivation achieved was approximate to 50%. Recovery of nAChR function did not return even after 5 h, whereas recovery from desensitization occurred within 20 min. Determinations of the concentration of nicotine in the superfusate indicated that residual nicotine could not account for the observed decrease in response as a consequence of desensitization. These results indicate that high concentrations of nicotine can produce a long-lasting nAChR inactivation which can be distinguished from reversible nAChR desensitization. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.