银杏叶提取物对超极化激活的环核苷酸门控基因编码的起搏通道电生理特性的影响

目的研究银杏叶提取物对异源表达在卵母细胞上的超极化激活的环核苷酸门控通道（HCN）2、4阻断的电药理学特性及分子机制。方法将人HCN2、4的mRNA显微注射到非洲爪蟾卵母细胞后,利用双电极电压钳技术记录通道电流。结果银杏叶提取物呈浓度依赖性阻滞表达在爪蟾卵母细胞上HCN2、4通道,药物半量抑制浓度IC50值分别为0.12±0.05 mg/ml和0.25±0.01 mg/ml。银杏叶提取物对HCN2、4通道阻断的阻断作用是不可逆的,经过15-20 min药物洗脱,阻滞的HCN电流部分并没有完全恢复到对照水平,只能恢复大约55%-75%。在-110 mV时银杏叶提取物对激活时间常数的值明显增大,对HCN2通道从504.6±39.8 ms（n=8）增为588.4±21.7 ms（0.03 mg/ml,n=8,P〈0.05）,1176.4±57.3 ms（0.3 mg/ml,n=8,P〈0.05）;对HCN4通道从1330.5±59.8 ms（n=8）增为1973.1±83.6 ms（0.03 mg/ml,n=8,P〈0.05）,而银杏叶提取物对HCN电流的去激活时间常数并未明显改变。结论银杏叶提取物以浓度依赖性方式不可逆的作用于HCN2、4通道,且对HCN4通道的抑制作用强于HCN2通道,减慢了通道的激活动力学,而对通道的去激活动力学无明显影响。

Effects of ginkgo biloba extract on pacemaker channels encoded by human hyperpolarization-activated cyclic nucleotide-gated gene expressed in xenopus laevis oocytes

Objective To investigate the electropharmacological activity of ginkgo biloba extract（ GBE） on human hyperpolarization-activated nucleotide-gated channel（ HCN） 2 and 4. Methods HCN mRNA were injected into Xenopus laevis oocytes. After 1-2 days incubation,standard two-electrode voltage-clamp recordings were employed to examine properties of HCN currents under GBE administration at 0. 01,0. 03,0. 1,0. 3 and 1 mg / ml Results HCN2 and HCN4 currents were inhibited by the GBE in a concentration-dependent manner. The value of half maximal inhibitory concentration（ IC 50） of HCN2 and HCN4 was 0. 25 ± 0. 01 mg / ml and 0. 12 ± 0. 05 mg / ml,respectively. Blockages of currents occurred rapidly in the presence of 0. 3 mg / ml GBE but apparently were not reversed after washout for 5min. After 15 to 20 min washout,the current failed to recover completely to control level,approximately was recovered to roughly 55%-75% of control values. The values of τactivation were increased markedly by GBE at- 110 mV from 504. 6 ± 39. 8ms（ n = 8） to 588. 4 ± 21. 7 ms（ 0. 03 mg / ml,n = 8,P 0. 05） and 1176. 4 ± 57. 3 ms（ 0. 3 mg / ml,n = 8,P 0. 05）,1330. 5 ± 59. 8 ms（ n = 8） to 1973. 1 ± 83. 6 ms（ 0. 03 mg / ml,n = 8,P 0. 05） and 2814. 5 ± 107. 6 ms（ 0. 3 mg / ml,n = 8,P 0. 05）,respectively. However,compared with the control,GBE did not significantly affect the deactivation curves of the HCN currents. Conclusion The GBE irreversibly reduces HCN2 and HCN4 currents in a concentration-dependent style,markedly shifts the activation curve of hHCN2 and hHCN4 currents toward more negative potentials and dramatically slows the kinetics of activation,but not that of deactivation.