Differential effects of chronic drug treatment on α3 * and α7 nicotinic receptor binding sites, in hippocampal neurones and SH‐SY5Y cells

The aim of this study was to compare the effects of chronic treatment (for 4 or 7 days) with nicotinic drugs and 20 m M KCl on numbers of surface α7 nicotinic AChR, identified by [ 125 I]‐α bungarotoxin (α‐Bgt) binding, in primary hippocampal cultures and SH‐SY5Y cells. Numbers of α3 * nicotinic AChR were also examined in SH‐SY5Y cells, using [ 3 H]‐epibatidine, which is predicted to label the total cellular population of predominantly α3β2 * nicotinic AChR under the conditions used. All the nicotinic agonists examined, the antagonists d‐tubocurarine and methyllycaconitine, and KCl, upregulated [ 125 I]‐α Bgt binding sites by 20–60% in hippocampal neurones and, where examined, SH‐SY5Y cells. Upregulation of [ 125 I]‐α‐Bgt binding sites by KCl was prevented by co‐incubation with the L‐type Ca 2+ channel blocker verapamil or the Ca 2+ ‐calmodulin dependent kinase II (CaM‐kinase II) inhibitor KN‐62. Upregulation of [ 125 I]‐α‐Bgt binding sites by nicotine or 3,[(4‐dimethylamino) cinnamylidene] anabaseine maleate (DMAC) was insensitive to these agents. [ 3 H]‐Epibatidine binding sites in SH‐SY5Y cells were not affected by KCl but were upregulated in a verapamil‐insensitive manner by nicotine and DMAC. KN‐62 itself provoked a 2 fold increase in [ 3 H]‐epibatidine binding. The inactive analogue KN‐04 had no effect, suggesting that CaM‐kinase II plays a role in regulating numbers of α3 * nicotinic AChR. These data indicate that numbers of α3 * and α7 nicotinic AChR are modulated differently. Nicotinic agonists and KCl upregulate α7 nicotinic AChR through distinct cellular mechanisms, the latter involving L‐type Ca 2+ channels and CaM‐kinase II. In contrast, α3 * nicotinic AChR are not upregulated by KCl. This difference may reflect the distinct physiological roles proposed for α7 nicotinic AChR.British Journal of Pharmacology (2001) 133 , 1286–1295; doi: 10.1038/sj.bjp.0704207