Chronic Menthol Does Not Change Stoichiometry or Functional Plasma Membrane Levels of Mouse 34-Containing Nicotinic Acetylcholine Receptors.

Heteromeric 34 nicotinic acetylcholine (ACh) receptors (nAChRs) are pentameric ligand-gated cation channels that include at least two 3 and two 4 subunits. They have functions in peripheral tissue and peripheral and central nervous systems. We examined the effects of chronic treatment with menthol, a major flavor additive in tobacco cigarettes and electronic nicotine delivery systems, on mouse 34 nAChRs transiently transfected into neuroblastoma-2a cells. Chronic menthol treatment at 500 nM, near the estimated menthol concentration in the brain following cigarette smoking, altered neither the [ACh]-response relationship nor Zn sensitivity of ACh-evoked currents, suggesting that menthol does not change 34 nAChR subunit stoichiometry. Chronic menthol treatment failed to change the current density (peak current amplitude/cell capacitance) of 100 M ACh-evoked currents. Chronic menthol treatment accelerated desensitization of 100 and 200 M ACh-evoked currents. Chronic nicotine treatment (250 M) decreased ACh-induced currents, and we found no additional effect of including chronic menthol. These data contrast with previously reported, marked effects of chronic menthol on 2* nAChRs studied in the same expression system. Mechanistically, the data support the emerging interpretation that both chronic menthol and chronic nicotine act on nAChRs in the early exocytotic pathway, and that this pathway does not present a rate-limiting step to the export of 34 nAChRs; these nAChRs include endoplasmic reticulum (ER) export motifs but not ER retention motifs. Previous reports show that smoking mentholated cigarettes enhances tobacco addiction; but our results show that this effect is unlikely to arise via menthol actions on 34 nAChRs.