大鼠海马CA1区神经元Na^+通道在出生后早期发育的变化

Changes of Na^+ channels in rat hippocampal CA1 neurons in early development after birth

为了探索大鼠海马CA1区锥体神经元电压门控性Na+通道发育的关键期,本研究采用膜片钳技术,分别对急性分离的出生后0周、1周、2周、3周、4周的大鼠海马CA1区锥体神经元进行全细胞记录。结果显示,随着大鼠出生后周龄的增大,Na+通道的最大电流密度逐渐增大,出生后1~4周相对于出生后0周的最大电流密度的增幅分别为(42.76±4.91)%、(146.80±7.63)%、(208.79±5.28)%、(253.72±5.74)%(n=10,P<0.05),出生后1周与2周之间的增幅最为显著;Na+通道的稳态激活曲线向左移动,出生后0~2周的半数激活电压逐渐减小,分别为39.06±0.65、43.41±0.52、48.29±0.45(mV,n=10,P<0.05),出生后2~4周的半数激活电压变化不大,出生后0~4周的斜率因子没有显著变化;Na+通道的稳态失活曲线及半数失活电压没有显著变化,但出生后1~2周斜率因子减小,分别为5.77±0.56、4.42±0.43(n=10,P<0.05),出生后0~1周、2~4周之间的斜率因子没有明显变化;Na+通道失活后恢复曲线左移,出生后1~3周的恢复时间常数逐渐减小,分别为8.30±0.24、7.15±0.21、6.18±0.25(ms,n=10,P<0.05),而出生后0~1周、3~4周之间没有明显变化;随着出生后的发育,海马CA1区锥体神经元动作电位发生变化,超射值与最大上升速率增大,阈值降低,与Na+电流的变化一致。结果提示,出生后1~2周可能是电压门控性Na+通道发育的关键期,此期间Na+通道分布显著增加,激活曲线左移,失活速度变快,失活后恢复的时间缩短。

The purpose of this research is to investigate the critical period of voltage-gated Na＋ channel development in hippocampal CA1 neurons. Changes ofNa＋ currents in acutely isolated hippocampal CA1 neurons of rats at different ages （0-4 weeks after birth） were recorded using the whole-cell patch-clamp technique. The results indicated that the maximum current density of Na＋ channels was increasing with age, and the amplitudes in 1, 2, 3 and 4 weeks respectively grew by （42.76 ± 4.91）%, （146.80 ± 7.63）%, （208.79 ± 5.28）% and （253.72 ± 5.74）% （n = 10, P 〈 0.05） compared with that in 0 week. The current density in CA1 neurons of 1-2 weeks after birth increased more significantly than those of other groups. The activation curve ofNa＋ channel shifted to the left. The half-activa- tion voltages （mV） in 0-2 weeks were -39.06 ± 0.65, -43.41 ± 0.52, -48.29 ± 0.45 （n = 10, P 〈 0.05）, respectively, showing signifi- cant age-dependent decrease, and there were no significant changes in other groups. The slope factors of activation curve for each group did not change significantly. There were no regular changes in inactivation curve and no significant changes in half-inactivation voltage. The slope factors of inactivation curve in 1-2 weeks were： 5.77 ± 0.56, 4.42 ± 0.43 （n = 10, P 〈 0.05）. The inactivation rate of the second week after birth was faster than that of the first week, and there were no significant changes during 0-1 week and 2-4 weeks. The recovery from inactivation curve ofNa＋ channel shifted to the left. The recovery time declined in 1-3 weeks. Changes of action potential properties were consistent with Na＋ current. These results suggest that the period of 1-2 weeks after birth may be the critical development period of voltage-gated Na＋channel in hippocampal CA1 neurons. During this time, the distribution ofNa＋ channel increases significantly; the activation curve ofNa＋ channel shifts to the left; inactivation rate increases as well as recovery time shortens.