Kinetics of anandamide transport through planar lipid bilayers: effect of cholesterol.

<p>Planar lipid bilayers consisting of pure POPC (full triangles), or various mixtures of POPC and cholesterol [molar∶ molar 2∶1 (full squares), 4∶1 (open squares), 5∶1 (full circles), 8∶1 (open circles)] were obtained as described for electrical measurements. <i>A</i>. Anandamide (1 mM) was added to the cis compartment in presence of 4.2 mM MβCD. The amount of anandamide recovered in the trans compartment was enzymatically measured using an anandamide assay with 5-lipoxygenase. <i>B</i>. Anandamide transport as a function of cholesterol percentage in the POPC bilayer. The experimental points correspond to the amount of AEA in the trans compartment 1 hour after its addition in the cis compartment. The sigmoidal shape of the cholesterol effect suggests that a threshold level of cholesterol is required to trigger the translocation of AEA. This is consistent with the recruitment of cholesterol molecules into tail-to-tail dimers as the ordered supramolecular cholesterol structure used by AEA to cross the membrane. On the opposite, a further excess of cholesterol (full squares, panel A) would condense into non functional nanodomains unable to further increase the kinetics of AEA transport.