The position of the double bond in monounsaturated free fatty acids is essential for the inhibition of the nicotinic acetylcholine receptor

PERILLO, V. L.; FERNÁNDEZ NIEVAS, G. A.; VALLES, A. S.; BARRANTES, F. J.; ANTOLLINI, S. S.

BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2012 vol. 1818 p. 2511 - 2520

0005-2736

Free fatty acids (FFAs) are non-competitive antagonists of the nicotinic acetylcholine receptor (AChR). Their site of action is supposedly located at the lipid-AChR interface. To elucidate the mechanism involved in this antagonism, we studied the effect that FFAs with a single double-bond at different positions (w6, w9, w11 and w13 cis-18:1) have on different AChR properties. Electrophysiological studies showed that only two FFAs (w6 and w9) reduced the duration of the channel open-state. The briefest component of the closed time distribution remained unaltered, suggesting that w6 and w9 behave as allosteric blockers. Fluorescence resonance energy transfer studies indicated that all FFAs locate at the lipid-AChR interface, ù6 being restricted to annular sites and all others occupying non-annular sites. The perturbation of the native membrane order by FFAs was evaluated by DPH (1,6-diphenyl-1,3,5-hexatriene) and Laurdan fluorescence polarization studies, with the greatest decrease observed for w9 and w11. AChR conformational changes produced by FFAs present at the lipid bilayer were evaluated by fluorescence quenching studies of pyrene-labeled AChR and also using the AChR conformational-sensitive probe crystal violet. All cis-FFAs produced AChR conformational changes at the transmembrane level, but only w9, w11 and w13 perturbed the resting state. Thus, the position and isomerism of the torsion angle of unsaturated FFAs are probably a key factor in terms of AChR blockage, suggesting that FFAs with a unique cis double bond at a superficial position inside the membrane directly inhibit AChR function by perturbing a potential conserved core structure for AChR gating at that level.