Abstract: The synergetic mechanisms of deltamethrin and phoxim mixtures were studied on cell from a mesencephalic dopaminergic cell line MN-9D using the patch-clamp technique. The results showed that these mixtures were more powerful inhibitors of sodium currents than single pesticides, more rapidly reducing the action potential and blocking the nerve impulse of axon membrane. Recording of whole cell sodium currents showed that slow decaying tail currents were associated with repolarization following a depolarizing pulse in deltamethrin modified cells. The average constant of tail currents was concentration independent. Most cells showed a marked reduction in peak current with only a few showing an increase. The inhibition of sodium channels was concentration-dependent and could not recover later. We concluded that deltamethrin modified the action kinetics of sodium channels in such a way as to slow opening, prolong closure or otherwise inactivate them and that this modification occurs predominantly when the channels are in the closed or resting state. The inhibition of sodium currents will cause the reduction of action potential and loss of electrical excitability of axon membrane.

Key words: deltamethrin, phoxim, sodium channel, mixture synergy