Suzuki H, Yanagisawa M, Yoshioka K, Hosoki R, Otsuka M
Department of Pharmacology, Faculty of Medicine, Tokyo Medical and Dental University, Japan.
Neurosci Res. 1997 Jul;28(3):261-7. doi: 10.1016/s0168-0102(97)00052-7.
The possible involvement of enzymatic degradation in the inactivation of enkephalins in the spinal cord of neonatal rats was investigated electrophysiologically and biochemically. In an isolated spinal cord-saphenous nerve preparation, electrical stimulation of the saphenous nerve evoked a slow depolarization lasting 20-30 s of the ipsilateral L3 ventral root. This slow depolarization was depressed by a mixture of peptidase inhibitors, consisting of actinonin (10 microM), thiorphan (0.6 microM), bestatin (10 microM), arphamenine B (10 microM) and captopril (10 microM). Naloxone (0.5 microM) not only reversed this effect of the mixture of peptidase inhibitors but also potentiated the slow depolarization beyond the pre-control level. In an isolated spinal cord preparation, electrical stimulation of a lumbar dorsal root evoked a slow depolarization of the contralateral ventral root of the same segment. This slow depolarization was depressed by application of [Met5]enkephalin in a dose dependent manner. This effect of [Met5]enkephalin was markedly potentiated by addition of the mixture of peptidase inhibitors. Among the five peptidase inhibitors, actinonin, thiorphan or bestatin alone potentiated the depressant effect of [Met5]enkephalin, whereas arphamenine B and captopril did not. Membrane fractions prepared from neonatal rat spinal cords showed degrading activities for [Met5]- and [Leu5]enkephalins and these activities were inhibited by the mixture of peptidase inhibitors. Among the five peptidase inhibitors, actinonin and thiorphan markedly inhibited the [Met5]enkephalin-degrading activity while bestatin was less effective. Arphamenine B and captopril were ineffective. The present results suggest that enzymatic degradation by peptidases plays a role in the termination of the transmitter action of enkephalins in the neonatal rat spinal cord. The present results, together with our previous results on the enzymatic degradation of tachykinins in a study in which we used the same preparations, suggest that similar but distinct combinations of peptidases are involved in the inactivation of enkephalin and tachykinin neurotransmitters.
用电生理学和生物化学方法研究了酶促降解在新生大鼠脊髓中脑啡肽失活过程中可能发挥的作用。在离体脊髓 - 隐神经标本中，电刺激隐神经可诱发同侧L3腹根持续20 - 30秒的缓慢去极化。这种缓慢去极化被由抑肽酶（10微摩尔）、硫氧还蛋白（0.6微摩尔）、贝司他汀（10微摩尔）、阿弗曼宁B（10微摩尔）和卡托普利（10微摩尔）组成的肽酶抑制剂混合物所抑制。纳洛酮（0.5微摩尔）不仅逆转了肽酶抑制剂混合物的这种作用，还使缓慢去极化增强至超过对照前水平。在离体脊髓标本中，电刺激腰背根可诱发同一节段对侧腹根的缓慢去极化。这种缓慢去极化被[Met5]脑啡肽以剂量依赖方式抑制。添加肽酶抑制剂混合物可显著增强[Met5]脑啡肽的这种作用。在这五种肽酶抑制剂中，单独使用抑肽酶、硫氧还蛋白或贝司他汀可增强[Met5]脑啡肽的抑制作用，而阿弗曼宁B和卡托普利则无此作用。从新生大鼠脊髓制备的膜组分显示出对[Met5]-和[Leu5]脑啡肽的降解活性，这些活性被肽酶抑制剂混合物所抑制。在这五种肽酶抑制剂中，抑肽酶和硫氧还蛋白显著抑制[Met5]脑啡肽的降解活性，而贝司他汀的作用较弱。阿弗曼宁B和卡托普利无效。目前的结果表明，肽酶的酶促降解在新生大鼠脊髓中脑啡肽递质作用的终止中发挥作用。目前的结果，连同我们之前在一项研究中使用相同标本对速激肽酶促降解的结果，表明类似但不同的肽酶组合参与了脑啡肽和速激肽神经递质的失活。
