The Pore Loop Domain of TRPV1 Is Required for Its Activation by the Volatile Anesthetics Chloroform and Isoflurane

Abstract

The environmental irritant chloroform, a naturally occurring small volatile organohalogen, briefly became the world's most popular volatile general anesthetic (VGA) before being abandoned because of its low therapeutic index. When chloroform comes in contact with skin or is ingested, it causes a painful burning sensation. The molecular basis for the pain associated with chloroform remains unknown. In this study, we assessed the role of transient receptor potential (TRP) channel family members in mediating chloroform activation and the molecular determinants of VGA activation of TRPV1. We identified the subpopulation of dorsal root ganglion (DRG) neurons that are activated by chloroform. Additionally, we transiently expressed wild-type or specifically mutated TRP channels in human embryonic kidney cells and used calcium imaging or wholecell patch-clamp electrophysiology to assess the effects of chloroform or the VGA isoflurane on TRP channel activation. The results revealed that chloroform activates DRG neurons via TRPV1 activation. Furthermore, chloroform activates TRPV1, and it also activates TRPM8 and functions as a potent inhibitor of the noxious chemical receptor TRPA1. The results also indicate that residues in the outer pore region of TRPV1 previously thought to be required for either proton or heat activation of the channel are also required for activation by chloroform and isoflurane. In addition to identifying the molecular basis of DRG neuron activation by chloroform and the opposing effects chloroform has on different TRP channel family members, the findings of this study provide novel insights into the structural basis for the activation of TRPV1 by VGAs.

Location and Character of Volatile General Anesthetics Binding Sites in the Transmembrane Domain of TRPV1

“…Our computational work supports a model where anesthetics occupy multiple sites with a total of five sites identified, in agreement with experimental studies. 23,75 It has been proposed that chloroform and isoflurane could activate TRPV1 via similar mechanisms 23 by using overlapping regions in the pore loop site I. This is in agreement with reported studies showing that hydrophilic-polar interfaces bind volatile anesthetics.…”

“…Therefore, the pain receptor TRPV1 was reported to display agonist-dependent activation stoichiometry. 28 Chloroform became the most popular volatile general anesthetic of the 19th century, before being abandoned because of its low therapeutic index, 23 but has recently regained interest as having been reported to activate the TRPV1 ion channel at millimolar concentrations using a similar mechanism as isoflurane. In particular, experimental data has suggested that TRPV1 is directly activated by chloroform, and none of the other heat-activated channels (TRPV2, TRPV3 or TRPV4) are activated by chloroform at clinical concentrations that are reported to elicit a robust activation of TRPV1.…”

Lysophosphatidic acid activates satellite glia cells and Schwann cells

“…We also obtained this substance dissolved in chloroform, but all procedures employed to evaporate chloroform caused remaining activation of neurons from a pure (LPA‐free) chloroform solution handled identically. It should be noted that chloroform activates TRPV1 (Kimball, Luo, Yin, Hu, & Dhaka, ). The 1‐myristoyl‐2‐hydroxy‐sn‐glycero‐3‐phosphate sodium salt (product 857120P; LPA 14:0) served as control lysophospholipid.…”

Overactivation of the sodium–calcium exchanger and transient receptor potential in anesthesia‐induced malignant hyperthermia

“…Strikingly, TRPV1 has of late been demonstrated to be sensitive to volatile anesthetics in neurons . However, the potential ramifications of TRPV1 channel in the system prompting changed the balance of Ca 2+ level and its association with the pathophysiology of MH has not yet been explored.…”