No abstract

1 Nicotinic drug treatment can affect the expression of neuronal nicotinic acetylcholine receptors (nAChR) both in vivo and in vitro through molecular mechanisms not fully understood. The present study investigated the effect of the novel cytisine dimer 1,2-bisN-cytisinylethane (CC4) on nAChR natively expressed by SH-SY5Y neuroblastoma cells in culture. 2 CC4 lacked the agonist properties of cytisine and was a potent antagonist (IC 50 ¼ 220 nM) on nAChRs. Chronic treatment of SH-SY5Y cells with 1 mM CC4 for 48 h increased the expression of 3 H-epibatidine ( 3 H-Epi; 3-4-fold) or 125 I-a-bungarotoxin ( 125 I-aBgtx; 1.2-fold) sensitive receptors present on the cell membrane and in the intracellular pool. Comparable data were obtained with nicotine or cytisine, but not with carbamylcholine, d-tubocurarine, di-hydro-b-erythroidine or hexametonium. 3 Immunoprecipitation and immunopurification studies showed that the increase in 3 H-Epi-binding receptors was due to the enhanced expression of a3b2 and a3b2b4 subtypes without changes in subunit mRNA transcription or receptor half-life. The upregulation was not dependent on agonist/antagonist properties of the drugs, and did not concern muscarinic or serotonin receptors. 4 Whole-cell patch clamp analysis of CC4-treated cells demonstrated larger nicotine-evoked inward currents with augmented sensitivity to the blockers a-conotoxin MII or methyllycaconitine. 5 In conclusion, chronic treatment with CC4 increased the number of nAChRs containing b2 and a7 subunits on the plasma membrane, where they were functionally active. In the case of b2-containing receptors, we propose that CC4, by binding to intracellular receptors, triggered a conformational reorganisation of intracellular subunits that stimulated preferential assembly and membrane-directed trafficking of b2-containing receptor subtypes.