This study examined the mechanism of action of a local anesthetic, lidocaine.HCl. Energy transfer between the surface fluorescent probe, 1-anilinonaphthalene-8-sulfonic acid, and the hydrophobic fluorescent probe, 1,3-di(1-pyrenyl) propane, was used to determine the effect of lidocaine.HCl on the thickness (D) of the synaptosomal plasma membrane vesicles (SPMV) isolated from the bovine cerebral cortex, and liposomes of the total lipids (SPMVTL) and phospholipids (SPMVPL) extracted from the SPMV. The thickness (D) of the intact SPMV, SPMVTL and SPMVPL were 1.044+/-0.008, 0.914+/-0.005 and 0.890+/-0.003 (arbitrary units, n=5) at 37degrees C (pH 7.4), respectively. Lidocaine.HCl decreased the thickness of the neuronal and model membrane lipid bilayers in a dose-dependent manner with a significant decrease in the thickness, even at 0.1 mM. The decreasing effect of lidocaine.HCl on the membrane thickness might be responsible for some, but not all of its anesthetic action.
Anilino Naphthalenesulfonates ; Cell Membrane ; Cerebral Cortex ; Energy Transfer ; Lipid Bilayers ; Liposomes ; Membranes ; Neurons ; Phospholipids ; Propane

BACKGROUNDVolatile 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.

METHODSReal-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.

RESULTSThe 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.

CONCLUSIONSOur 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.

Adenosine Monophosphate ; analysis ; Anesthetics, Inhalation ; pharmacology ; Anilino Naphthalenesulfonates ; Calmodulin ; antagonists & inhibitors ; chemistry ; physiology ; Cyclic Nucleotide Phosphodiesterases, Type 1 ; analysis ; Fluorescence ; Humans ; Hydrophobic and Hydrophilic Interactions

We have developed a rapid and high throughput lipase-ANS (8-Anilino-l-naphthalenesulfonic acid) assay to evaluate the thermo-stability of lipases based on the ANS fluorescence signal's increasing and shifting when this small fluorescence probes binds to lipase. The testing lipase samples were incubated at a temperature range of 25 degrees C to 65 degrees C for 30 min before mixed with ANS solution (0.20 mg/mL lipase and 0.05 mmol/L ANS in the buffer of 20 mmol/L Tris-HCl, 100 mmol/L NaCl, pH 7.2) in a cuvette or microplate. Fluorescence signals of the samples were measured at EX 378 nm, EM 465 nm with a fluorescence photometer or a plate reader, and Tm was calculated with the software of GraphPad Prism5.0. The Tm values of several mutants of Penicillium expansum lipase (PEL) were measured with this ANS assay and conventional method simultaneously and the results show that Tm values are comparative and consistent between these methods, suggesting that the lipase-ANS assay is a reliable, rapid and high throughput method for lipase thermo-stability measurement.
Anilino Naphthalenesulfonates ; chemistry ; Enzyme Stability ; High-Throughput Screening Assays ; methods ; Hot Temperature ; Lipase ; metabolism ; Spectrometry, Fluorescence