Veale E L, Buswell R, Clarke C E, Mathie A
Medway School of Pharmacy, Universities of Kent and Greenwich at Medway, Kent, UK.
Br J Pharmacol. 2007 Nov;152(5):778-86. doi: 10.1038/sj.bjp.0707436. Epub 2007 Sep 10.
The TASK subfamily of two pore domain potassium channels (K2P) encodes for leak K currents, contributing to the resting membrane potential of many neurons and regulating their excitability. TASK1 and TASK3 channels are regulated by a number of pharmacological and physiological mediators including cannabinoids such as methanandamide. In this study, we investigate how methanandamide blocks these channels.
Currents through wild type and mutated TASK1 and TASK3 channels expressed in modified HEK-293 cells were measured using whole-cell electrophysiological recordings in the presence and absence of methanandamide.
Methanandamide (3 microM) produced substantial block of hTASK1, hTASK3 and mTASK3 channels but was most potent at blocking hTASK3 channels. Block of these channels was irreversible unless cells were washed with buffer containing bovine serum albumin. Mutation of the distal six amino acids of TASK1 did not alter methanandamide inhibition, whilst C terminal truncation of TASK3 channels caused a small but significant reduction of inhibition. However, deletion of six amino acids (VLRFLT) at the interface between the final transmembrane domain and cytoplasmic C terminus of TASK3 channels gave functional currents that were no longer inhibited by methanandamide or by activation of GPCRs.
Methanandamide potently blocked TASK3 and TASK1 channels and both methanandamide and G protein-mediated inhibition converged on the same intracellular gating pathway. Physiologically, methanandamide block of TASK1 and TASK3 channels may underpin a number of CNS effects of cannabinoids that are not mediated through activation of CB1 or CB2 receptors.
双孔钾通道（K2P）的TASK亚家族编码钾离子泄漏电流，该电流有助于许多神经元的静息膜电位，并调节其兴奋性。TASK1和TASK3通道受多种药理和生理介质调节，包括大麻素如N-花生四烯酸乙醇胺。在本研究中，我们探究了N-花生四烯酸乙醇胺如何阻断这些通道。
在存在和不存在N-花生四烯酸乙醇胺的情况下，使用全细胞膜片钳电生理记录技术测量在修饰的HEK-293细胞中表达的野生型及突变型TASK1和TASK3通道的电流。
N-花生四烯酸乙醇胺（3 microM）对人TASK1、人TASK3和小鼠TASK3通道产生显著阻断作用，但对人TASK3通道的阻断作用最强。除非用含有牛血清白蛋白的缓冲液洗涤细胞，否则这些通道的阻断是不可逆的。TASK1远端六个氨基酸的突变不改变N-花生四烯酸乙醇胺的抑制作用，而TASK3通道的C末端截短导致抑制作用有小幅但显著的降低。然而，删除TASK3通道最后一个跨膜结构域与胞质C末端之间界面处的六个氨基酸（VLRFLT）后产生的功能性电流不再受N-花生四烯酸乙醇胺或G蛋白偶联受体激活的抑制。
N-花生四烯酸乙醇胺有效阻断TASK3和TASK1通道，且N-花生四烯酸乙醇胺和G蛋白介导的抑制作用都汇聚于同一细胞内门控途径。在生理上，N-花生四烯酸乙醇胺对TASK1和TASK3通道的阻断可能是大麻素许多中枢神经系统效应的基础，这些效应并非通过CB1或CB2受体的激活介导。
