Trichloroethanol, an active metabolite of chloral hydrate, modulates tetrodotoxin-resistant Na+ channels in rat nociceptive neurons

BackgroundChloral hydrate is a sedative-hypnotic drug widely used for relieving fear and anxiety in pediatric patients. However, mechanisms underlying the chloral hydrate-mediated analgesic action remain unexplored. Therefore, we investigated the effect of 2 ',2 ',2 '-trichloroethanol (TCE), the active metabolite of chloral hydrate, on tetrodotoxin-resistant (TTX-R) Na+ channels expressed in nociceptive sensory neurons.MethodsThe TTX-R Na+ current (I-Na) was recorded from acutely isolated rat trigeminal ganglion neurons using the whole-cell patch-clamp technique.ResultsTrichloroethanol decreased the peak amplitude of transient TTX-R I-Na in a concentration-dependent manner and potently inhibited persistent components of transient TTX-R I-Na and slow voltage-ramp-induced I-Na at clinically relevant concentrations. Trichloroethanol exerted multiple effects on various properties of TTX-R Na+ channels; it (1) induced a hyperpolarizing shift on the steady-state fast inactivation relationship, (2) increased use-dependent inhibition, (3) accelerated the onset of inactivation, and (4) retarded the recovery of inactivated TTX-R Na+ channels. Under current-clamp conditions, TCE increased the threshold for the generation of action potentials, as well as decreased the number of action potentials elicited by depolarizing current stimuli.ConclusionsOur findings suggest that chloral hydrate, through its active metabolite TCE, inhibits TTX-R I-Na and modulates various properties of these channels, resulting in the decreased excitability of nociceptive neurons. These pharmacological characteristics provide novel insights into the analgesic efficacy exerted by chloral hydrate.