Not just any free fatty acid inhibits the nicotinic acetylcholine receptor

Abstract

To elucidate the mechanism involved in the non-competitive inhibition of the nicotinic acetylcholine receptor (AChR) caused by free fatty acids (FFAs), we studied the effect of FFAs with a single double-bond at different positions ( 6, 9, 11 and 13, cis-18:1) on different AChR properties. Two FFAs ( 6 and 9) reduced the duration of the channel open-state. The briefest component of the closed-time distribution remained unaltered, suggesting that 6 and 9 do not behave as typical open-channel blockers but rather as allosteric blockers. Fluorescence resonance energy transfer studies showed that all FFAs locate at the lipid-AChR interface, 6 being restricted to annular sites and all others occupying non-annular sites. Fluorescence quenching studies of pyrene-labeled AChR indicate that all cis-FFAs produce AChR conformational changes at the transmembrane level. Using the AChR conformationalsensitive probe crystal violet, we observed that all unsaturated FFAs increase its K in the AChR desensitized state, but only 9, D 11 and 13 cis-18:1 decrease its K in the resting state. In D conclusion, some FFAs appear to directly inhibit AChR function probably by localizing at superficial sites inside the membrane, whereas other FFAs modulate the receptor´s conformational states by a different mechanism.