5, 10, or 20 mg/kg

Female Wistar rats Cerebral cortex homogenate were used for activity evaluation. Binding assays were performed in 1-ml volumes of Tris HC1 buffer for 90 min at 20°C using cere- brocortical membranes containing approximately 200 mkg of protein. After incubation, each sample was filtered under vacuum through Whatman GF/B filters using a Brandel cell harvester to separate bound and free radioactivity. Filter retained (bound) radioactivity was extracted for at least 8 h in 4 ml of scintillation fluid before estimation using a beta-scintillation counter. Estimated radioactivity was quench cor¬rected with an average [3H] counting efficiency of 60.4%. In order to determine if local anaesthetics interacted with DHP binding sites on L-type Ca2+ channels, the DHP binding site was labelled with [3H]PN200-110. Increasing concentrations of unlabelled displacer (local anaesthetics) were then added. Displacement of [3H]PN200-110 binding by local anaesthetics indicates that they are interact-ing at the same site as the radiolabel. A fixed concentration of [3H]PN200-110 (approximately 0.2 nmol litre-1) was displaced by the following unlabelled agents Amylocaine (30-10000mkM)