Abstract
The effects of the dihydropyrazole insecticide RH-3421 on the tetrodotoxin-resistant (TTX-R) voltage-gated sodium channels in rat dorsal root ganglion (DRG) neurons were studied using the whole-cell patch clamp technique. RH-3421 at 10 nM to 1 μM completely blocked action potentials. The sodium currents were irreversibly suppressed by 1 μM RH-3421 in a time- and a dose-dependent manner and the IC 50 value of RH-3421 was estimated to be 0.7 μM after 10 min of application. RH-3421 blocked the sodium currents to the same extent over the entire range of test potentials. The sodium conductance–voltage curve was not shifted along the voltage axis by 1 μM RH-3421 application. In contrast, both fast and slow steady-state sodium channel inactivation curves were shifted in the hyperpolarizing direction in the presence of 1 μM RH-3421. It was concluded that RH-3421 bound to the resting and inactivated sodium channels to cause block with a higher affinity for the latter state.
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