Neurotoxic implications of the agonistic action of CS-syndrome pyrethroids on the N-type Ca(v)2.2 calcium channel.

BACKGROUND

Cismethrin (T-syndrome) and deltamethrin (CS-syndrome) pyrethroids have been previously shown to increase membrane depolarization and calcium influx, but only deltamethrin increased Ca(2+)-dependent neurotransmitter release from rat brain synaptosomes. Deltamethrin's action was blocked by omega-conotoxin GVIA, delineating a separate action at N-type Ca(v)2.2 channels that is consistent with the in vivo release of neurotransmitter. It is hypothesized that other CS-syndrome pyrethroids will elicit similar actions at presynaptic nerve terminals.

RESULTS

Nine additional pyrethroids were similarly examined, and these data were used in a cluster analysis. CS-syndrome pyrethroids that possessed alpha-cyano groups, cypermethrin, deltamethrin and esfenvalerate, all caused Ca(2+) influx and neurotransmitter release and clustered with two other alpha-cyano pyrethroids, cyfluthrin and cyhalothrin, that shared these same actions. T-syndrome pyrethroids, bioallethrin, cismethrin and fenpropathrin, did not share these actions and clustered with two non-alpha-cyano pyrethroids, tefluthin and bifenthrin, which likewise did not elicit these actions. Deltamethrin reduced peak current of heterologously expressed wild-type Ca(v)2.2, increased peak current of T422E Ca(v)2.2 and was 20-fold more potent on T422E Ca(v)2.2 than on wild-type channels, indicating that the permanently phosphorylated form of Ca(v)2.2 is the preferred target.

CONCLUSIONS

Ca(v)2.2 is directly modified by deltamethrin, but the resulting perturbation is dependent upon its phosphorylation state. The present findings may provide a partial explanation for the different toxic syndromes produced by these structurally distinct pyrethroids.