title: Volatile anesthetics inhibit the activity of calmodulin by interacting with its hydrophobic site.
abstract: BACKGROUND
  Volatile anesthetics (VAs) may affect varied and complex physiology processes by manipulating Ca(2+)-calmodulin (CaM). However, the detailed mechanism about the action of VAs on CaM has not been elucidated. This study was undertaken to examine the effects of VAs on the conformational change, hydrophobic site, and downstream signaling pathway of CaM, to explore the possible mechanism of anesthetic action of VAs.
  
  
  METHODS
  Real-time second-harmonic generation (SHG) was performed to monitor the conformational change of CaM in the presence of VAs, each plus 100 µmol/L Ca(2+). A hydrophobic fluorescence indicator, 8-anilinonaphthalene-1-sulfonate (ANS), was utilized to define whether the VAs would interact with CaM at the hydrophobic site or not. High-performance liquid chromatography (HPLC) was carried out to analyze the activity of CaM-dependent phosphodiesterase (PDE1) in the presence of VAs. The VAs studied were ether, enflurane, isoflurane, and sevoflurane, with their aqueous concentrations 7.6, 9.5, 11.4 mmol/L; 0.42, 0.52, 0.62 mmol/L; 0.25, 0.31, 0.37 mmol/L and 0.47, 0.59, 0.71 mmol/L respectively, each were equivalent to their 0.8, 1.0 and 1.2 concentration for 50% of maximal effect (EC50) for general anesthesia.
  
  
  RESULTS
  The second-harmonic radiation of CaM in the presence of Ca(2+) was largely inhibited by the VAs. The fluorescence intensity of ANS, generated by binding of Ca(2+) to CaM, was reversed by the VAs. HPLC results also showed that AMP, the product of the hydrolysis of cAMP by CaM-dependent PDE1, was reduced by the VAs.
  
  
  CONCLUSIONS
  Our findings demonstrate that the above VAs interact with the hydrophobic core of Ca(2+)-CaM and the interaction results in the inhibition of the conformational change and activity of CaM. This in vitro study may provide us insight into the possible mechanism of anesthetic action of VAs in vivo.
authors.affiliation: Department of Anesthesiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, China.
authors.forename: Miao-Miao
authors.initials: MM
authors.lastname: Zhou
authors.forename: Hui-Min
authors.initials: HM
authors.lastname: Xia
authors.forename: Jiao
authors.initials: J
authors.lastname: Liu
authors.forename: You-Nian
authors.initials: YN
authors.lastname: Xu
authors.forename: Nai-Xin
authors.initials: NX
authors.lastname: Xin
authors.forename: Shi-Hai
authors.initials: SH
authors.lastname: Zhang
mesh_terms: D000249:Adenosine Monophosphate / Q000032:analysis; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000817:Anilino Naphthalenesulfonates; D002147:Calmodulin / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000502:physiology; D054677:Cyclic Nucleotide Phosphodiesterases, Type 1 / Q000032:analysis; D005453:Fluorescence; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions
chemical_list: D018685:Anesthetics, Inhalation; D000817:Anilino Naphthalenesulfonates; D002147:Calmodulin; D000249:Adenosine Monophosphate; D054677:Cyclic Nucleotide Phosphodiesterases, Type 1