High affinity binding of 3H-verapamil to rat brain synaptic membrane is antagonized by pyrethroid insecticides

Deltamethrin is a powerful neuroactive agent causing increased neurotransmitter release at the synapse. To understand the cause for such an action of this pyrethroid insecticide, we have studied its binding characteristics to the calcium channel by utilizing 3H-verapamil as a specific ligand. It was found that deltamethrin is capable of competing at the same binding site as 3H-verapamil. Also, it was found that nonlabeled verapamil could reduce the binding of 3H-deltamethrin (tested at 1 nM) to its binding site. The EC50 value of verapamil to displace 50% of 3H-deltamethrin was in the order of 0.3 microM, which coincides with the approximate KD value for this ligand to bind with calcium channels in the rat brain synaptosomal plasma membranes.