Correlation between enhancement of [ 3H]flunitrazepam binding and suppression of pentylenetetrazol-induced seizures by L-lysine

Abstract

L-Lysine enhanced the specific [ 3H]flunitrazepam (FTZ) binding of bovine brain membranes in vitro. Inhibition of specific [ 3H]FTZ binding to brain membranes in vitro by pentylenetetrazol (PTZ) at concentrations 0.46 mM and below was reversed by increasing L-lysine concentrations in the incubation mixture; further increase of L-lysine concentration enhanced this binding. However, inhibition of [ 3H]FTZ binding by PTZ higher than 2.3 mM was reversed only partially by L-lysine. L-Lysine enhanced specific [ 35S]t-butylbicyclophosphorothionate (TBPS) binding on mouse brain membranes in a dose-dependent manner (EC ≈ 5 μM). This enhancement was inhibited by PTZ dose dependently. Inhibition of [ 35S]TBPS binding by PTZ was attenuated slightly by L-lysine. L-Lysine enhanced [ 3H]FTZ binding in intact mice in a dose- or concentration-dependent manner with an ED 50 of 6 mmol/kg body weight or EC 50 of 3 μmol/g brain tissue, respectively. Similar effect was observed for L-lysine in ex vivo [ 3H]FTZ binding study when [ 3H]FTZ was incubated in vitro with an ED 50 of 1 mmol/kg mouse or EC 50 of 0.7 μmol/g brain. PTZ not only induced seizures, but also inhibited specific [ 3H]FTZ binding to brain membranes in a dose-dependent manner. L-Lysine, in a dose-dependent manner, suppressed seizures caused by PTZ at 50 or 60 mg/kg, or prolonged the time of seizure onset (seizure latency) caused by higher doses of PTZ (90 or 100 mg/kg). Pretreatment with L-lysine at 1, 5, 10 or 20 mmol/kg not only reversed the inhibition of the specific [ 3H]FTZ binding caused by PTZ at 50, 90 or 100 mg/kg, but also enhanced this binding above control level. A positive correlation with correlation coefficient of 0.79 to 0.98 was observed between the enhancement of specific [ 3H]FTZ binding and increase of seizure latency against PTZ-induced seizures for mice pretreated with L-lysine.