Different conformational status of AChR induced by steroids and free fatty acids.

FERNÁNDEZ NIEVAS, G.A.; ANTOLLINI, S. S.; BARRANTES, F. J.

Rosario, Santa Fe, Argentina

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2006

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Steroids and free fatty acids (FFA) are no competitive inhibitors of the nicotinic acetylcholine receptor (AChR). They are purportedly located at the lipid-AChR interface, and their exact mechanism of action is still unknown. We studied the effect of FFA and steroids on AChR conformational equilibrium in T. californica AChR-rich membranes using the probe crystal violet (CrV), which displays higher affinity for the desensitized conformation (D) than for the resting conformation (R). Increasing concentrations of steroids (cortisone, hydrocortisone) shifted the equilibrium towards the D form even in the absence of agonist. In contrast, different FFA stabilized the AChR in a conformation with low affinity for CrV, similar to that of the R state, even in the presence of agonist. Cholesterol-depletion of AChR-rich membranes through cyclodextrin treatment led to an AChR conformation similar to that resulting from FFA. Both FFA and cholesterol depletion increase lipid fluidity, whereas steroids decrease it, as measured by Laurdan generalized polarization using Förster energy transfer conditions. Thus, AChR conformational states disclosed by CrV fluorescence can be correlated to the physical state of the AChR lipid microenvironment.