Effect of alpha-cypermethrin and theta-cypermethrin on delayed rectifier potassium currents in rat hippocampal neurons.

Cypermethrin is a photostable synthetic pyrethroid and the most widely used Type II pyrethroid pesticide. The effects of two different stereoisomers of cypermethrin insecticides, alpha-cypermethrin and theta-cypermethrin, on the delayed rectifier potassium current (IK) in hippocampal neurons of rat, were studied using whole-cell patch clamp technique. Alpha-cypermethrin and theta-cypermethrin decreased the amplitude value of IK, and shifted the steady state activation curve of IK towards negative potential at any concentrations (10(-9) M, 10(-8) M, 10(-7) M). Furthermore, at higher concentration, alpha-cypermethrin (10(-7) M) and theta-cypermethrin (10(-8) M, 10(-7) M) had observable effects of the steady state inactivation of IK. The results suggest that IK is the target of alpha-cypermethrin and theta-cypermethrin, which may explain the mechanism of toxic effects of both steroeisomers of cypermethrin on mammalian neurons. Cypermethrin-altered properties of voltage gated delayed rectifier K+ channels may contribute to neurotoxicity by eliciting abnormal electrical discharges in hippocampal CA3 neurons.