GABA(A) receptor subtype selectivity of the proconvulsant rodenticide TETS

The rodenticide tetramethylenedisulfotetramine (TETS) is a potent convulsant (lethal dose in humans 7–10 mg) that is listed as a possible threat agent by the United States Department of Homeland Security. TETS has previously been studied in vivo for toxicity and in vitro in binding assays, with the latter demonstrating it to be a non-competitive antagonist on GABA(A) receptors. To determine whether TETS exhibits subtype selectivity for a particular GABA(A) receptor combination, we used whole-cell patch-clamp to determine the potency of TETS on the major synaptic and extrasynaptic GABA(A) receptors associated with convulsant activity. The active component of picrotoxin, picrotoxinin, was used as a control. While picrotoxinin did not differentiate well between 13 GABA(A) receptors, TETS exhibited the highest activity on α2β3γ2 (IC(50) 480 nM, 95% CI 320–640 nM) and α6β3γ2 (IC(50) 400 nM, 95% CI 290–510 nM). Introducing β1 or β2 subunits into these receptor combinations reduced or abolished TETS sensitivity, suggesting that TETS preferentially affects receptors with α2/β3 or α6/β3 composition. Since α2β3γ2 receptors make up 15–20% of the GABA(A) receptors in the mammalian CNS, we suggest that α2β3γ2 is probably the most important GABA(A) receptor for the seizure-inducing activity of TETS.