Harinath S, Sikdar S K
Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India.
Epilepsy Res. 2005 May;64(3):127-35. doi: 10.1016/j.eplepsyres.2005.03.002.
Caffeine (1,3,7-trimethylxanthine) and theophylline (1,3-dimethylxanthine) are used for therapeutic purposes and can cause life-threatening convulsive seizures due to systemic toxicity. The mechanisms for the epileptogenicity of caffeine and theophylline are not clear. TWIK-related K(+) channels (TREK-1) are highly expressed in the human central nervous system and have a major role in the control of neuronal excitability by regulating the resting membrane potential. In view of their physiological significance, inhibition of TREK-1 channels may be implicated in caffeine- and theophylline-induced seizures. We thus investigated, using whole-cell patch-clamp technique, modulation of hTREK-1 channels expressed in Chinese hamster ovary (CHO) cells by caffeine and theophylline. Caffeine and theophylline produced reversible inhibition of TREK-1 channels in a concentration-dependent manner. The half-maximal inhibitory concentrations (IC(50)) for caffeine and theophylline were 377+/-54microM and 486+/-76microM, respectively. Caffeine and theophylline depolarized the membrane potential of CHO(TREK-1) cells in a reversible and concentration-dependent manner. Inhibition by caffeine (5mM) and theophylline (2mM) was attenuated in TREK-1 channels with mutation of the PKA consensus sequence at serine 348, suggesting the involvement of cAMP/PKA pathway in the inhibitory process. Inhibition of TREK-1 channels and consequent membrane depolarization may contribute to the convulsive seizures induced by toxic levels of caffeine and theophylline.
咖啡因（1,3,7 - 三甲基黄嘌呤）和茶碱（1,3 - 二甲基黄嘌呤）用于治疗目的，但由于全身毒性可导致危及生命的惊厥发作。咖啡因和茶碱致痫性的机制尚不清楚。TWIK相关钾通道（TREK - 1）在人类中枢神经系统中高度表达，通过调节静息膜电位在控制神经元兴奋性方面起主要作用。鉴于其生理意义，TREK - 1通道的抑制可能与咖啡因和茶碱诱导的癫痫发作有关。因此，我们使用全细胞膜片钳技术研究了咖啡因和茶碱对中国仓鼠卵巢（CHO）细胞中表达的hTREK - 1通道的调节作用。咖啡因和茶碱以浓度依赖性方式对TREK - 1通道产生可逆性抑制。咖啡因和茶碱的半数最大抑制浓度（IC50）分别为377±54μM和486±76μM。咖啡因和茶碱以可逆且浓度依赖性方式使CHO（TREK - 1）细胞的膜电位去极化。在丝氨酸348处PKA共有序列发生突变的TREK - 1通道中，咖啡因（5mM）和茶碱（2mM）的抑制作用减弱，表明cAMP/PKA途径参与了抑制过程。TREK - 1通道的抑制及随之而来的膜去极化可能导致咖啡因和茶碱中毒水平引起的惊厥发作。
