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

ABSTRACT: Neuronal nicotinic acetylcholine receptors (nAChRs) containing the ?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 (?5DN), has recently been associated with increased use of tobacco and higher incidence of lung cancer. We show that in ventral midbrain neurons, the ?5 subunit is essential for heteromeric nAChR-induced intracellular-free Ca(2+) concentration elevations and that in ?5(-/-) mice, a class of large-amplitude nicotine-evoked currents is lost. Furthermore, the expression of the ?5DN subunit is not able to restore nicotinic responses, indicating a loss of function by this subunit in native neurons. To understand how ?5DN impairs heteromeric nAChR functions, we coexpressed ?4, ?5, or ?5DN subunits with a dimeric concatemer (?2?4) in a heterologous system, to obtain nAChRs with fixed stoichiometry. Both ?5(?2?4)2 and ?5DN(?2?4)2 nAChRs yielded similar levels of functional expression and Ca(2+) permeability, measured as fractional Ca(2+) currents (8.2 ± 0.7% and 8.0 ± 1.9%, respectively), 2-fold higher than ?4(?2?4)2. Our results indicate that the loss of function of nicotinic responses observed in ?5DN-expressing ventral midbrain neurons is neither due to an intrinsic inability of this subunit to form functional nAChRs nor to an altered Ca(2+) permeability but likely to intracellular modulation.

SUBMITTER: Sciaccaluga M 

PROVIDER: S-EPMC4511205 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature