INSECTICIDAL ACTIVITY OF SIKIMI EXTRACT AND ITS MODULATION OF THE GABA(A) RECEPTOR-CHANNEL

Sikimi plant (also known as Japanese star anise), Illicium anisatium, is toxic to mammals. Extracts of Sikimi were studied for their insecti cidal activity against the larvae of mosquito, Culex quinquefasciatus, and for their mechanism of action on ion channels. Crude methanol ext ract and its ethyl acetate-soluble fractions were insecticidally activ e, with EC50 values of 63.0 mu g ml(-1) and 43.7 mu g ml(-1), respecti vely. The ethyl acetate-soluble fraction was perfused through the bath ing solution and the current induced by a brief (10 ms) application of GABA by pressure ejection through pipette electrode was recorded by t he whole-cell patch clamp technique. The extract suppressed GABA-induc ed currents irreversibly with an EC50 value of 0.42 mu g ml(-1). The t ime constant of current fitted to the single exponential function was shortened by the ethyl acetate-soluble fraction at concentrations rang ing from 0.1 mu g ml(-1) to 10 mu g ml(-1) in a concentration-dependen t manner. It was concluded that Sikimi extracts decreased the affinity of GABA for its binding site on the GABA receptor, thereby suppressin g GABA-induced currents. (C) 1998 SCI.