Scherer R W, Lo C F, Breitwieser G E
Department of Physiology, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205.
J Gen Physiol. 1993 Jul;102(1):125-41. doi: 10.1085/jgp.102.1.125.
The effects of leukotriene C4 (LTC4) on activation of muscarinic acetylcholine receptor (mAChR)-stimulated, inwardly rectifying K+ current (IK[ACh]) were examined in single bullfrog atrial myocytes using the whole-cell patch clamp technique. LTC4 produced a reversible, concentration-dependent increase in steady-state, guanosine-gamma-thiotriphosphate (GTP gamma S)-activated IK[ACh], with a K0.5 of 3.1 microM. LTC4 also increased the rate of GTP gamma S-mediated IK[ACh] activation, both in the absence and presence of 1 nM ACh, with comparable K0.5 values of 4.7 microM under basal conditions and 4.9 microM in the presence of 1 nM ACh. LTC4 did not alter the relative affinities of the G protein, Gk, for GTP gamma S and GTP. We hypothesize that all of the effects of LTC4 on the kinetics of Gk-mediated IK[ACh] activation are produced at a common site with a K0.5 of 3-5 microM. The effects of LTC4 on IK[ACh] activation are fully reversible in the presence of GTP gamma S. Under physiological conditions (i.e., intracellular GTP), 10 microM LTC4 increased the ACh-activated peak IK[ACh]. Inhibitors of cellular LTC4 production, including 5,8,11,14-eicosatetraynoic acid, baicalein, cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate, and alpha-pentyl-4-(2-quinolinylmethoxy)-benzene methanol, greatly attenuated ACh-dependent IK[ACh] activation, preventing activation of peak, and producing a lower steady-state IK[ACh] (when compared with the control response in the same cell). Addition of exogenous LTC4 was able to overcome the effects of LTC4 synthesis inhibitors, restoring both the peak and steady-state IK[ACh] responses. Although the mechanism of LTC4-mediated modulation of IK[ACh] activation is not known, our results suggest that endogenously produced lipoxygenase metabolites of arachidonic acid, specifically LTC4, are involved in the physiological process of IK[ACh] activation.
运用全细胞膜片钳技术，在单个牛蛙心房肌细胞中研究了白三烯C4（LTC4）对毒蕈碱型乙酰胆碱受体（mAChR）刺激的内向整流钾电流（IK[ACh]）激活的影响。LTC4使稳态鸟苷-γ-硫代三磷酸（GTPγS）激活的IK[ACh]产生可逆的、浓度依赖性增加，其半数效应浓度（K0.5）为3.1微摩尔/升。在不存在和存在1纳摩尔乙酰胆碱（ACh）的情况下，LTC4均增加了GTPγS介导的IK[ACh]激活速率，在基础条件下和存在1纳摩尔ACh时的半数效应浓度（K0.5）值相当，分别为4.7微摩尔/升和4.9微摩尔/升。LTC4未改变G蛋白Gk对GTPγS和GTP的相对亲和力。我们推测，LTC4对Gk介导的IK[ACh]激活动力学的所有影响均在一个半数效应浓度（K0.5）为3至5微摩尔/升的共同位点产生。在存在GTPγS的情况下，LTC4对IK[ACh]激活的影响是完全可逆的。在生理条件下（即细胞内GTP），10微摩尔/升的LTC4增加了ACh激活的IK[ACh]峰值。细胞LTC4产生的抑制剂，包括5,8,11,14-二十碳四烯酸、黄芩素、肉桂酰-3,4-二羟基-α-氰基肉桂酸酯和α-戊基-4-（2-喹啉基甲氧基）-苯甲醇，极大地减弱了ACh依赖性IK[ACh]激活，阻止了峰值激活，并产生了较低的稳态IK[ACh]（与同一细胞中的对照反应相比）。添加外源性LTC4能够克服LTC4合成抑制剂的影响，恢复峰值和稳态IK[ACh]反应。虽然LTC4介导的IK[ACh]激活调节机制尚不清楚，但我们的结果表明，花生四烯酸的内源性产生的脂氧合酶代谢产物，特别是LTC4，参与了IK[ACh]激活的生理过程。
