Activation of K(+) current plays a critical role in the control of programmed cell death. In the present study, whole-cell patch-clamp recording, a caspase-3 activity assay, and flow cytometric analysis were used to examine the effects of the MT2 melatonin receptor agonist 2-iodomelatonin on the delayed-rectifier K(+) current (IK) and the prevention of apoptosis. It was found that apoptosis of cerebellar granular neurons induced by low-K(+) (5 mm) incubation was associated with an increase in IK amplitude and caspase-3 activity. After 6 hr of low-K(+) treatment, IK was increased by 45% (n = 86). Flow cytometry showed that the apoptosis rate increased by 333% compared with the control neurons. In addition, exposure of cultured granule cells to low K(+) also resulted in a significant activation of caspase-3, by 466%. 2-Iodomelatonin (10 microm in injection pipette) inhibited the IK amplitude recorded from control cells and from cells undergoing apoptosis. However, 2-iodomelatonin only modified the IK-channel activation kinetics of cells under both conditions. Furthermore, 2-iodomelatonin reduced the rate of apoptosis and caspase-3 activation, by 66 and 64%, respectively. The melatonin receptor antagonist, 4P-PDOT, abrogated the effect of 2-iodomelatonin on the IK augmentation, caspase-3 activity, and apoptosis. These results suggest that the neuroprotective effects of melatonin are not only because of its function as a powerful antioxidant, but also to its interactions with specific receptors. The effect of 2-iodomelatonin against apoptosis may be mediated by activating a melatonin receptor, which modulates IK channels and reduces K(+) efflux.

中文翻译：

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褪黑素受体激动剂2-碘降钙素通过K（+）电流抑制阻止小脑颗粒神经元的凋亡。

K（+）电流的激活在程序性细胞死亡的控制中起着关键作用。在本研究中，全细胞膜片钳记录，caspase-3活性测定和流式细胞仪分析被用来检查MT2褪黑素受体激动剂2-iodomelatonin对延迟整流器K（+）电流的影响（ IK）和细胞凋亡的预防。发现低K（+）（5 mm）孵育诱导的小脑颗粒神经元凋亡与IK振幅和caspase-3活性增加有关。低K（+）治疗6小时后，IK增加了45％（n = 86）。流式细胞仪检测结果表明，与对照组相比，细胞凋亡率提高了333％。此外，将培养的颗粒细胞暴露于低K（+）也会导致caspase-3的显着活化（466％）。2-碘降钙素（注射吸管中的10微米）抑制了从对照细胞和经历凋亡的细胞中记录的IK振幅。然而，2-碘降钙素仅在两种条件下均改变了细胞的IK-通道活化动力学。此外，2-碘降钙素分别使细胞凋亡和caspase-3激活率降低66％和64％。褪黑激素受体拮抗剂4P-PDOT废除了2-碘降钙素对IK增高，caspase-3活性和细胞凋亡的作用。这些结果表明，褪黑激素的神经保护作用不仅是因为其具有强大的抗氧化剂功能，还在于其与特定受体的相互作用。2-iodomelatonin对细胞凋亡的影响可能是通过激活褪黑激素受体介导的，该受体调节IK通道并降低K（+）外排。