甲硫-脑啡肽对大鼠DRG分离神经元ATP-激活内向电流的抑制

Inhibition of ATP-activated currents by met-Enk in isolated DRG neurons of the rat

本研究探讨了甲硫－脑啡肽（ｍｅｔ－Ｅｎｋ）对ＡＴＰ－激活电流（ＩＡＴＰ）的调制作用。实验在大鼠新鲜分离背根神经节（ＤＲＧ）神经元上进行。应用全细胞膜片钳技术所记录的ＩＡＴＰ为内向电流。在被检测的ＤＲＧ神经元中，９０．０％（４５／５０）的细胞对ＡＴＰ有反应。在４５个对ＡＴＰ感的细胞中：对大部分细胞（２９／４５）施加ｍｅｔ－Ｅｎｋ（１０－９～１０－５ ｍｏｌ／Ｌ）也引起一内向电流；少部分细胞（９／４５）为外向电流；其余的细胞（７／４５）未引起可检测的腹反应。预加ｍｅｔ－Ｅｎｋ后ＩＡＴＰ明显地被抑制，此种抑制作用为剂量依赖性的。在预加１０－９、１０－８、１０－７、１０－６、１０－５ ｍｏｌ／Ｌ ｍｅｔ－Ｅｎｋ后，ＩＡＴＰ的抑制分别为：１３．２±５．４％（ｎ＝５）、３９．２±８．６％（ｎ＝８）、５４．１±８．６％（ｎ＝ ８）、４３．３±７．９％（ｎ＝７）；４３．１±７．９％（ｎ＝７）（ｍｅａｎ±ＳＥＭ）。阿片肽拮抗剂纳洛酮能翻转此种抑制效应。ＩＡＴＰ的量－效关系表明，预加ｍｅｔ－Ｅｎｋ后曲线明显压低，在浓度为１０－３ｍｏｌ／Ｌ时ＩＡＴＰ下降约２５％，而Ｋｄ值几乎不变。

The present study aimed to explore modulation of ATP-activated currents (IATP) by met-Enk in rat DRG neurons. IATP were recorded using the whole-cell patch clamp technique. The majority of the neurons examined responded to ATP (90.0%, 45/50) with inward currents. In the 45 ATP sensitive neurons three kinds of responses to application of met-Enk were distinguished: (1) inward currents (29/45), (2) outward currents (9/45), and (3) no effect (7/45). Pretreatment with met-Enk (10-9~10-5 mol/L) suppressed IATP(10-4 mol/L) in 29 neurons responding to met-Enk with inward currents. The inhibition by met-Enk of IATP could be blocked by naloxone (10-7mol/L) in a concentration-dependent manner. Met-Enk of 10-9, 10-8, 10-7.10-6and 10-5 mol/L suppressed I ATP by 13.2±5.4% (n=5);39.2±8.6% (n=8),54.1 ±8.6%(n=8),43.3±7.9%(n=7)and 43.1±7.9%(n=7)(mean±MSE),respectively.A compar-ison of concentration - response relations of ATP with and without preapplication of met-Enk indicated that after pretreatment with met-Enk (10-7 rnol/L) the curve shifted downward markedly with a decrease of 25% of the maxmum value of IAPT and unchanged KD value. The suppression of IATP by met-Enk was reversed as evi-denced by intracellular dialysis of H-9 by using die repatch technique. Taken together, it is suggested that the inhibition by met-Enk of IATP is caused by activiation of opiate receptor, which eventurally results in phosphory- lation of ATP receptor, mediated by modulation of G protein coupling and intracellular signal transduction.