Ratnakumari L, Vysotskaya T N, Duch D S, Hemmings H C
Department of Anesthesiology, Weill Medical College of Cornell University, New York, New York 10021, USA.
Anesthesiology. 2000 Feb;92(2):529-41. doi: 10.1097/00000542-200002000-00037.
Despite their key role in the generation and propagation of action potentials in excitable cells, voltage-gated sodium (Na+) channels have been considered to be insensitive to general anesthetics. The authors tested the sensitivity of neuronal Na+ channels to structurally similar anesthetic (1-chloro-1,2,2-trifluorocyclobutane; F3) and nonanesthetic (1,2-dichlorohexafluorocyclobutane; F6) polyhalogenated cyclobutanes by neurochemical and electrophysiologic methods.
Synaptosomes (pinched-off nerve terminals) from adult rat cerebral cortex were used to determine the effects of F3 and F6 on 4-aminopyridine- or veratridine-evoked (Na+ channel-dependent) glutamate release (using an enzyme-coupled spectrofluorimetric assay) and increases in intracellular Ca2+ ([Ca2+]i) (using ion-specific spectrofluorimetry). Effects of F3 and F6 on Na+ currents were evaluated directly in rat lumbar dorsal root ganglion neurons by whole-cell patch-clamp recording.
F3 inhibited glutamate release evoked by 4-aminopyridine (inhibitory concentration of 50% [IC50] = 0.77 mM [approximately 0.8 minimum alveolar concentration (MAC)] or veratridine (IC50 = 0.42 mM [approximately 0.4 MAC]), and veratridine-evoked increases in [Ca2+]i (IC50 = 0.5 mM [approximately 0.5 MAC]) in synaptosomes; F6 had no significant effects up to 0.05 mM (approximately twice the predicted MAC). F3 caused reversible membrane potential-independent inhibition of peak Na+ currents (70+/-9% block at 0.6 mM [approximately 0.6 MAC]), and a hyperpolarizing shift in the voltage-dependence of steady state inactivation in dorsal root ganglion neurons (-21+/-9.3 mV at 0.6 mM). F6 inhibited peak Na+ currents to a lesser extent (16+/-2% block at 0.018 mM [predicted MAC]) and had minimal effects on steady state inactivation.
The anesthetic cyclobutane F3 significantly inhibited Na+ channel-mediated glutamate release and increases in [Ca2+]i. In contrast, the nonanesthetic cyclobutane F6 had no significant effects at predicted anesthetic concentrations. F3 inhibited dorsal root ganglion neuron Na+ channels with a potency and by mechanisms similar to those of conventional volatile anesthetics; F6 was less effective and did not produce voltage-dependent block. This concordance between anesthetic activity and Na+ channel inhibition supports a role for presynaptic Na+ channels as targets for general anesthetic effects and suggests that shifting the voltage-dependence of Na+ channel inactivation is an important property of volatile anesthetic compounds.
尽管电压门控钠（Na+）通道在可兴奋细胞动作电位的产生和传导中起关键作用，但一直被认为对全身麻醉药不敏感。作者通过神经化学和电生理方法测试了神经元Na+通道对结构相似的麻醉剂（1-氯-1,2,2-三氟环丁烷；F3）和非麻醉剂（1,2-二氯六氟环丁烷；F6）多卤代环丁烷的敏感性。
使用成年大鼠大脑皮层的突触体（ pinched-off神经末梢）来确定F3和F6对4-氨基吡啶或藜芦碱诱发的（Na+通道依赖性）谷氨酸释放（使用酶联荧光分光光度法）和细胞内Ca2+（[Ca2+]i）增加（使用离子特异性荧光分光光度法）的影响。通过全细胞膜片钳记录直接评估F3和F6对大鼠腰段背根神经节神经元Na+电流的影响。
F3抑制4-氨基吡啶诱发的谷氨酸释放（50%抑制浓度[IC50]=0.77 mM[约0.8最低肺泡浓度（MAC）]）或藜芦碱诱发的谷氨酸释放（IC50=0.42 mM[约0.4 MAC]），以及突触体中藜芦碱诱发的[Ca2+]i增加（IC50=0.5 mM[约0.5 MAC]）；F6在高达0.05 mM（约为预测MAC的两倍）时无显著影响。F3引起可逆的、与膜电位无关的峰值Na+电流抑制（在0.6 mM[约0.6 MAC]时阻断70±9%），并使背根神经节神经元稳态失活的电压依赖性发生超极化移位（在0.6 mM时为-21±9.3 mV）。F6对峰值Na+电流的抑制作用较小（在0.018 mM[预测MAC]时阻断16±2%），对稳态失活的影响最小。
麻醉性环丁烷F3显著抑制Na+通道介导的谷氨酸释放和[Ca2+]i增加。相比之下，非麻醉性环丁烷F6在预测的麻醉浓度下无显著影响。F3抑制背根神经节神经元Na+通道的效力和机制与传统挥发性麻醉剂相似；F6效果较差，且不产生电压依赖性阻断。麻醉活性与Na+通道抑制之间的这种一致性支持突触前Na+通道作为全身麻醉作用靶点的作用，并表明改变Na+通道失活的电压依赖性是挥发性麻醉化合物的一个重要特性。
