xe-991--anthracenone and rubidium-chloride

Linopirdine was developed as a cognitive enhancing molecule and demonstrated to specifically block the potassium current generated by the brain specific KCNQ2-KCNQ3 proteins (M-channel). In this study we investigated the relevance of [(3)H]linopirdine binding in rat brain extracts to the interaction with the M-channel proteins. Our results confirm the presence of a high affinity site for [(3)H]linopirdine in rat brain tissues (KD = 10 nM) but we also identified a high affinity binding site for [(3)H]linopirdine in rat liver tissues (KD = 9 nM). Competition experiments showed that [(3)H]linopirdine is displaced by unlabelled linopirdine with comparable affinities from its binding sites on rat brain and rat liver membranes. [(3)H]linopirdine was completely displaced by a set of cytochrome P450 (CYP450) ligands suggesting that [(3)H]linopirdine binding to rat brain and liver membranes is linked to CYP450 interaction. The testing of CYP450 ligands on the M-channel activity, using a Rb(+) efflux assay on cells expressing the KCNQ2-KCNQ3 proteins, demonstrated that [(3)H]linopirdine binding results cannot be correlated to M-channel inhibition. The results obtained in this study demonstrate that [(3)H]linopirdine binding to rat brain and rat liver membranes is representative for CYP450 interaction and not relevant for the binding to the M-channel proteins.

Topics: Animals; Anthracenes; Binding, Competitive; Brain; Cell Membrane; Chlorides; CHO Cells; Cricetinae; Cricetulus; Cytochrome P-450 CYP2D6; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Dose-Response Relationship, Drug; Indoles; KCNQ3 Potassium Channel; Ketoconazole; Kinetics; Liver; Male; Miconazole; Potassium Channels, Voltage-Gated; Pyridines; Pyrilamine; Quinidine; Radioligand Assay; Rats; Rats, Sprague-Dawley; Rubidium; Tritium