綠茶萃取物對初級培養大鼠胚胎神經細胞興奮性質的影響

Abstract

從綠茶中萃取出來的多酚化合物主要有四種成份：(–)-epigallocatechin gallate (EGCG), (–)-epigallocatechin (EGC), (–)-epicatechin gallate (ECG), and (–)-epicatechin (EC)。這些多酚已經被證實能夠抑制癌細胞的生長，防止神經退 化性疾病的形成，甚至能減少許多疾病的產生風險，像是中風、肥胖、心血管疾 病和老化。為了探討綠茶多酚對初級培養大鼠胚胎神經細胞的興奮性質有何影 響，我們利用全細胞膜片箝制技術去記錄離子通道電流和動作電位。研究結果顯 示ECG 減慢了電壓調控型鈉離子通道的不活化速率，而EC50 為12.88 ± 0.73 μM，同時此反應是可逆轉的；然而EGCG 卻沒有同樣的作用。鈉離子通道的不 活化恆穩態曲線也被ECG從-41.67 ± 0.08 毫伏特向負極移動到 -45.15 ± 0.05 毫 伏特。另外鈉離子通道從關閉狀態的恢復速率時間常數也從3.91 ± 0.08 毫秒延 長到 7.74 ± 0.43 毫秒。利用全細胞膜電流箝制技術記錄動作電位，ECG 會將電 作電位的強度和半寬分別從原先的96.5 ± 0.5 毫伏特和3.17 ± 0.13 毫秒增加到 103.9 ± 0.3 毫伏特和7.07 ± 0.12 毫秒，但是動作電位產生的頻率卻從16.4 ± 1.2 赫茲降到 6.6 ± 0.8 赫茲。這些研究結果顯示ECG 會經由影響鈉離子通道的性質 進一步改變神經細胞動作電位的產生，因而改變神經細胞的興奮性質。

ABSTRACT Polyphenols extracted from green tea (Camellia sinensis) is composed of four major chemicals: (–)-epigallocatechin gallate (EGCG), (–)-epigallocatechin (EGC), (–)-epicatechin gallate (ECG), and (–)-epicatechin (EC). These polyphenols have been shown to inhibit the growth of tumor cells, prevent neurodegenerative diseases, and reduce the risk of a series of illnesses, such as stroke, obesity, cardiovascular diseases, and aging. To study the effects of polyophenols on the excitability of primary cultured rat embryonic cortical neurons, whole-cell patch-clamp recording was used to monitor the ionic currents and action potential firing. The result showed that ECG reversibly slowed the inactivation of voltage-gated sodium channels with an EC50 of 12.88 ± 0.73 μM; however, EGCG did not have any effect on Na+ current. The steady-state inactivation of Na+ channel was negatively shifted from -41.67 ± 0.08 to -45.15 ± 0.05 mV and the time constant required for the recovery of Na+ channel to close state was prolonged from 3.91 ± 0.08 to 7.74 ± 0.43 ms by ECG. When action potentials were elicited under current clamp mode, the amplitude and half-width were increased from 96.5 ± 0.5 to 103.9 ± 0.3 mV and 3.17 ± 0.13 to 7.07 ± 0.12 ms, respectively; but frequency was decreased from 16.4 ± 1.2 to 6.6 ± 0.8 Hz. The results suggest that ECG may modulate excitability of neurons through altering sodium channels.