Crucial role of nicotinic alpha 5 subunit variants for Ca2+ fluxes in ventral midbrain neurons

• Published in: The FASEB journal Vol. 29; no. 8; pp. 3389 - 3398
• Main Authors: Sciaccaluga, Miriam, Moriconi, Claudia, Martinello, Katiuscia, Catalano, Myriam, Bermudez, Isabel, Stitzel, Jerry A, Maskos, Uwe, Fucile, Sergio
• Format: Journal Article
• Language: English
• Published: 24-08-2015
• ISSN: 0892-6638
• DOI: 10.1096/fj.14-268102

Neuronal nicotinic acetylcholine receptors (nAChRs) containing the alpha 5 subunit modulate nicotine consumption, and the human CHRNA5 rs16969968 polymorphism, causing the replacement of the aspartic acid residue at position 398 with an asparagine ( alpha 5DN), has recently been associated with increased use of tobacco and higher incidence of lung cancer. We show that in ventral midbrain neurons, the alpha 5 subunit is essential for heteromeric nAChR-induced intracellular-free Ca2+ concentration elevations and that in alpha 5-/- mice, a class of large-amplitude nicotine-evoked currents is lost. Furthermore, the expression of the alpha 5DN subunit is not able to restore nicotinic responses, indicating a loss of function by this subunit in native neurons. To understand how alpha 5DN impairs heteromeric nAChR functions, we coexpressed alpha 4, alpha 5, or alpha 5DN subunits with a dimeric concatemer ( beta 2 alpha 4) in a heterologous system, to obtain nAChRs with fixed stoichiometry. Both alpha 5( beta 2 alpha 4)2 and alpha 5DN( beta 2 alpha 4)2 nAChRs yielded similar levels of functional expression and Ca2+ permeability, measured as fractional Ca2+ currents (8.2 plus or minus 0.7% and 8.0 plus or minus 1.9%, respectively), 2-fold higher than alpha 4( beta 2 alpha 4)2. Our results indicate that the loss of function of nicotinic responses observed in alpha 5DN-expressing ventral midbrain neurons is neither due to an intrinsic inability of this subunit to form functional nAChRs nor to an altered Ca2+ permeability but likely to intracellular modulation.-Sciaccaluga, M., Moriconi, C., Martinello, K., Catalano, M., Bermudez, I., Stitzel, J. A., Maskos, U., Fucile, S. Crucial role of nicotinic alpha 5 subunit variants for Ca2+ fluxes in ventral midbrain neurons.