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Unsaturated Free Fatty Acids Effects On The Conformational State And Function Of Nicotinic Acetylcholine Receptor
PERILLO, V.L.; VALLÉS, A.S.; BARRANTES, F.J.; ANTOLLINI, S.S.
Otro; FEBS/EMBO Advanced Lecture Course "Biomembrane Dynamics: from molecules to cells"; 2011
Institut d'Etudes Scientifiques Cargèse
Free fatty acids (FFA) are non-competitive antagonists of the nicotinic acetylcholine receptor (AChR) and their site of action is supposedly located at the lipid-AChR interface, where lipids can be annular or non-annular. It is known that the cis-unsaturated FFA, and not trans-unsaturated FFA, produce conformational modifications in the AChR resting state. Using T. californica receptor-rich membranes, we studied the changes in AChR conformational state generated by differences in the double-bond position of monounsaturated FFA. Using the higher affinity of the fluorescent AChR blocker crystal violet for the desensitized than for the resting state, it was observed that all the unsaturated FFA increase the KD of the AChR in the desensitized state, but not the saturated FFA. FFA with double bonds in positions ω9, ω11 or ω13 also decrease the KD values in the resting state. Fluorescence extinction measurements of pyrene-labeled AChR indicate that the presence of a FFA with a double bond in position ω6, ω9, ω11 or ω13 produce AChR conformational changes at the transmembrane level. DPH and Laurdan fluorescence studies showed that fluidity increased the most in FFA with ω9 and ω11 double bonds and that ω6 and ω13 had less effect. Fluorescence resonance energy transfer experiments showed that the FFA with an ω6 double bond remained as an annular lipid whereas all the others also interact at non-annular sites. Electrophysiological studies show a decrease in the open time of the channel but no effect in the briefest component of the closed time of the channel suggesting that these FFA block the AChR but do not act as open-channel blockers. Thus, the location of the unsaturated double bond appears to be of critical importance for FFA-AChR interaction. Supported by grants from Mincyt, CONICET and UNS to FJB and SSA