In studies of muscle relaxation effect on rats and cats, NK433 was administered either parenterally via a cannula previously inserted into the jugular, cephalic or femoral vein. In oral administration study, NK433 was dissolved in distilled water and was administered via a cannula previously inserted into the stomach. NK433 reduced the mono- and polysynaptic reflex potential at doses of 5 and 10 mg/kg, i.v.

Binding to Voltage-gated sodium channels was studied using [3H]batrachotoxinin A 20-alpha-benzoate ([3H]-BTX) assay with rat cerebrocortical synaptosomes. Aliquots (100 μL) equal to approximately 6 to 8 mg/ml protein were used in [3H]BTX binding experiments. Binding assays were performed in the presence of 5.0 nM [3H]BTX, 1 μΜ tetrodotoxin, 4.0 μg of scorpion toxin, and various concentrations of the added drugs at 37°C for 60-min incubation time. Nonspecific binding was determined in the presence of 300 μΜ aconitine. The reaction was terminated by rapid filtration using a UniFilter-96 GF/B (PerkinElmer Life and Analytical Sciences). The filtration plates were washed five times with ice-cold wash buffer. Radioactivity trapped on a 96-well filtration plate was measured by liquid scintillation spectrometry in 40 μL of Mi-croscint 20 scintillation cocktail. Binding affinity of lanperisone was determined to be 13.7 uM.