The effects of chronic treatment (3 days) with the nicotinic agonists, nicotine and cytisine as well as the antagonists, d-tubocurarine, hexamethonium and dihydro-beta-erythroidine (DH beta E) on alpha 4 beta 2 nicotinic acetylcholine receptors (nAChRs) were investigated in a permanently transfected cell line, M10. The number of alpha 4 beta 2 nAChRs expressed in the cell line was assayed by (-)-[3H]nicotine binding. The two enantiomers of nicotine both significantly increased the number of nAChRs in a concentration dependent manner. No changes in the levels of mRNA for either alpha 4 or beta 2 subunits were found following chronic (-)-nicotine treatment. The effect of (-)-nicotine treatment on the number of nAChRs was partially blocked by the antagonists d-tubocurarine and hexamethonium, but not by dihydro-beta-erythroidine (DH beta E). Chronic exposure of the cells to each of the antagonists did not influence the number of nAChRs. Treatment with the agonist cytisine resulted in a bell-shaped dose-dependent effect on the number of alpha 4 beta 2 nAChRs. In the presence of cytisine (microM) the effect induced by chronic(-)-nicotine treatment on the number of the nAChRs was attenuated. These results indicate that nicotinic agents can induce different regulatory effects in M10 cells due to their individual pharmacological properties as agonist and/or antagonist.