IV anaesthetic agents do not interact with the verapamil binding site on L-type voltage-sensitive Ca2+ channels

In this study we have examined if the i.v. anaesthetic agents thiopentone, pentobarbitone, ketamine, etomidate, propofol and alphaxalone interact with the verapamil binding site on L-type voltage-sensitive Ca2+ channels in rat cerebrocortical membranes. Binding assays were performed in 1 ml volumes of Tris HCl 50 mmol litre(-1), pH 7.4, for 90 min at 20 degrees C, with cerebrocortical membranes (200 mu g of protein), the verapamil binding sites of which were radiolabelled with [H-3]verapamil. Non-specific binding was defined in the presence of verapamil 10(-6) mol litre(-1). The interaction of i.v. anaesthetics was determined by displacement of [H-3]verapamil 0.2 nmol litre(-1). The mean concentrations of anaesthetic producing 25% inhibition of specific binding (corrected for the competing mass of [H-3]verapamil), K-25, were (mmol litre(-1)): thiopentone 0.68 (SEM 0.14); pentobarbitone 1.22 (0.13); propofol 0.66 (0.10); etomidate 0.24 (0.03); alphaxalone 0.19 (0.02); and ketamine 0.75 (0.04). These concentrations exceeded those seen during anaesthesia and suggest that the neuronal verapamil binding site may not be an important target for i.v. anaesthetic agents.