Center for Stroke Research and Department of Experimental Neurology, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany.
Institute of Computer-Assisted Cardiovascular Medicine, Deutsches Herzzentrum der Charité, Berlin, Germany, and Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Berlin, Germany.
Anesthesiology. 2023 Jun 1;138(6):611-623. doi: 10.1097/ALN.0000000000004553.
Maintenance of ion homeostasis is essential for normal brain function. Inhalational anesthetics are known to act on various receptors, but their effects on ion homeostatic systems, such as sodium/potassium-adenosine triphosphatase (Na+/K+-ATPase), remain largely unexplored. Based on reports demonstrating global network activity and wakefulness modulation by interstitial ions, the hypothesis was that deep isoflurane anesthesia affects ion homeostasis and the key mechanism for clearing extracellular potassium, Na+/K+-ATPase.
Using ion-selective microelectrodes, this study assessed isoflurane-induced extracellular ion dynamics in cortical slices of male and female Wistar rats in the absence of synaptic activity, in the presence of two-pore-domain potassium channel antagonists, during seizures, and during spreading depolarizations. The specific isoflurane effects on Na+/K+-ATPase function were measured using a coupled enzyme assay and studied the relevance of the findings in vivo and in silico.
Isoflurane concentrations clinically relevant for burst suppression anesthesia increased baseline extracellular potassium (mean ± SD, 3.0 ± 0.0 vs. 3.9 ± 0.5 mM; P < 0.001; n = 39) and lowered extracellular sodium (153.4 ± 0.8 vs. 145.2 ± 6.0 mM; P < 0.001; n = 28). Similar changes in extracellular potassium and extracellular sodium and a substantial drop in extracellular calcium (1.5 ± 0.0 vs. 1.2 ± 0.1 mM; P = 0.001; n = 16) during inhibition of synaptic activity and two-pore-domain potassium suggested a different underlying mechanism. After seizure-like events and spreading depolarization, isoflurane greatly slowed extracellular potassium clearance (63.4 ± 18.2 vs. 196.2 ± 82.4 s; P < 0.001; n = 14). Na+/K+-ATPase activity was markedly reduced after isoflurane exposure (greater than 25%), affecting specifically the α2/3 activity fraction. In vivo, isoflurane-induced burst suppression resulted in impaired extracellular potassium clearance and interstitial potassium accumulation. A computational biophysical model reproduced the observed effects on extracellular potassium and displayed intensified bursting when Na+/K+-ATPase activity was reduced by 35%. Finally, Na+/K+-ATPase inhibition with ouabain induced burst-like activity during light anesthesia in vivo.
The results demonstrate cortical ion homeostasis perturbation and specific Na+/K+-ATPase impairment during deep isoflurane anesthesia. Slowed potassium clearance and extracellular accumulation might modulate cortical excitability during burst suppression generation, while prolonged Na+/K+-ATPase impairment could contribute to neuronal dysfunction after deep anesthesia.
离子动态平衡的维持对于正常的大脑功能至关重要。吸入麻醉剂已知作用于各种受体，但它们对离子动态平衡系统（如钠/钾-三磷酸腺苷酶（Na+/K+-ATPase））的影响在很大程度上仍未得到探索。基于报告表明间质离子可调节全脑网络活动和觉醒，因此假设深度异氟醚麻醉会影响离子动态平衡和清除细胞外钾的关键机制，即 Na+/K+-ATPase。
本研究使用离子选择性微电极，在无突触活动、存在双孔钾通道拮抗剂、癫痫发作和播散性去极化期间，评估雄性和雌性 Wistar 大鼠皮质切片中异氟醚诱导的细胞外离子动力学。使用偶联酶测定法测量异氟醚对 Na+/K+-ATPase 功能的特定影响，并研究体内和体外研究结果的相关性。
临床相关的异氟醚浓度可抑制爆发抑制麻醉，增加基础细胞外钾（平均值±标准差，3.0±0.0 与 3.9±0.5 mM；P<0.001；n=39）并降低细胞外钠（153.4±0.8 与 145.2±6.0 mM；P<0.001；n=28）。在抑制突触活动和双孔钾通道时，细胞外钾和细胞外钠的类似变化以及细胞外钙（1.5±0.0 与 1.2±0.1 mM；P=0.001；n=16）的大幅下降表明存在不同的潜在机制。癫痫样事件和播散性去极化后，异氟醚大大减缓了细胞外钾的清除（63.4±18.2 与 196.2±82.4 s；P<0.001；n=14）。Na+/K+-ATPase 活性在异氟醚暴露后显著降低（大于 25%），特别是影响α2/3 活性分数。在体内，异氟醚诱导的爆发抑制导致细胞外钾清除受损和间质钾积累。计算生物物理模型再现了观察到的细胞外钾效应，并显示当 Na+/K+-ATPase 活性降低 35%时，爆发加剧。最后，在体内轻度麻醉时，Na+/K+-ATPase 抑制用哇巴因诱导爆发样活动。
结果表明，在深度异氟醚麻醉期间，皮质离子动态平衡受到干扰，Na+/K+-ATPase 特异性受损。钾清除和细胞外积累的减缓可能会调节爆发抑制产生期间的皮质兴奋性，而 Na+/K+-ATPase 损伤的延长可能导致深度麻醉后神经元功能障碍。
