アフリカツメガエル卵母細胞に発現したセロトニントランスポーターに対する麻酔薬の作用

Serotonin (5-hydroxytryptamine, 5-HT) transporter (SERT) is the only functional membrane protein responsible for efficient synaptic clearance of extracellular 5-HT which has psychotogenic properties. Anesthetics clinically contribute to psychosedation to relieve phobia or anxiety accompanied with dental treatment. Nevertheless, little is known about the effects of anesthetics on SERT. In this study, [^3H]5-HT uptake assay and two-electrode voltage-clamp method were utilized to examine directly the effects of anesthetics on the human SERT expressed in Xenopus oocytes. Ketamine (1-100μM) significantly inhibited SERT function in concentration- and voltage dependent manners (IC_<50>=4μM). Eadie-Hofstee analysis showed a significant increase in Km (control ; 2.37±0.83μM, 10μM of ketamine ; 12.11±4.69μM) with no significant changes in the apparent Vmax (control ; 12.60±1.14pmol/oocyte/hr, 10μM of ketamine ; 14.67±2.66pmol/oocyte/hr), suggesting that ketamine competitively inhibited [^3H]5-HT uptake. Propofol inhibited [^3H]5-HT uptake and 5-HT-induced inward current only at high concentration (100μM). Pentobarbital (5-500μM) did not have significant effect on SERT function. Neither sevoflurane (50μM-2mM) nor isoflurane (50μM-2mM) had significant effect to SERT functiton. Interestingly, lidocaine (10nM-1μM) inhibited [^3H]5-HT uptake in a dose-dependent manner and [^3H]5-HT uptake was completely inhibited by 1μM of lidocaine. Eadie-Hofstee analysis showed a significant decrease in Vmax (control ; 13.28±2.07μM, 500nM of lidocaine ; 9.33±1.14μM) with no significant changes in Km (control ; 15.98±6.26pmol/oocyte/hr, 500nM of Lidocaine ; 15.81±4.91pmol/oocyte/hr), suggesting that lidocaine non-competitively inhibited [^3H]5-HT uptake. Intracellular QX314 (permanently charged lidocaine analogue) inhibited the [^3H]5-HT uptake by SERT, but intracellular or extracellular benzocaine (permanently uncharged local anesthetics) was without effect. These results suggest that the action sites of lidocaine on SERT seem to be located intracellularly. The effect of lidocaine was partially abolished in the present of staurosporine, protein kinase C inhibitor. In conclusion, these results suggest that ketamine and lidocaine directly inhibit SERT function at clinical concentrations, and PKC may partially be responsible for lidocaine-induced inhibition of SERT function.

公開日:2010年1月24日で登録したコンテンツは、国立情報学研究所において電子化したものです。