Markov Dmitriy, Mosharov Eugene V, Setlik Wanda, Gershon Michael D, Sulzer David
Department of Neurology, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA.
J Neurochem. 2008 Dec;107(6):1709-21. doi: 10.1111/j.1471-4159.2008.05737.x. Epub 2008 Jan 11.
Acute exposure to amphetamines (AMPHs) collapses secretory vesicle pH gradients, which increases cytosolic catecholamine levels while decreasing the quantal size of catecholamine release during fusion events. AMPH and methamphetamine (METH), however, are retained in tissues over long durations. We used optical and electron microscopic probes to measure the effects of long-term METH exposure on secretory vesicle pH, and amperometry and intracellular patch electrochemistry to observe the effects on neurosecretion and cytosolic catecholamines in cultured rat chromaffin cells. In contrast to acute METH effects, exposure to the drug for 6-48 h at 10 microM and higher concentrations produced a concentration-dependent rebound hyperacidification of secretory vesicles. At 5-10 microM levels, prolonged METH increased the quantal size and reinstated exocytotic catecholamine release, although very high (> 100 microM) levels of the drug, while continuing to produce rebound hyperacidification, did not increase quantal size. Secretory vesicle rebound hyperacidification was temperature dependent with optimal response at approximately 37 degrees C, was not blocked by the transcription inhibitor, puromycin, and appears to be a general compensatory response to prolonged exposure with membranophilic weak bases, including AMPHs, methylphenidate, cocaine, and ammonia. Thus, under some conditions of prolonged exposure, AMPHs and other weak bases can enhance, rather than deplete, the vesicular release of catecholamines via a compensatory response resulting in vesicle acidification.
急性接触苯丙胺类药物（AMPHs）会破坏分泌囊泡的pH梯度，这会增加胞质儿茶酚胺水平，同时在融合事件期间降低儿茶酚胺释放的量子大小。然而，AMPH和甲基苯丙胺（METH）会在组织中长时间留存。我们使用光学和电子显微镜探针来测量长期接触METH对分泌囊泡pH的影响，并使用安培法和细胞内膜片电化学来观察对培养的大鼠嗜铬细胞中神经分泌和胞质儿茶酚胺的影响。与急性METH效应相反，在10 microM及更高浓度下将药物暴露6 - 48小时会导致分泌囊泡出现浓度依赖性的反弹超酸化。在5 - 10 microM水平时，长时间的METH会增加量子大小并恢复儿茶酚胺的胞吐释放，尽管非常高（> 100 microM）的药物水平虽然继续产生反弹超酸化，但并未增加量子大小。分泌囊泡的反弹超酸化依赖于温度，在约37摄氏度时反应最佳，不受转录抑制剂嘌呤霉素的阻断，并且似乎是对长时间暴露于包括AMPHs、哌甲酯、可卡因和氨在内的亲膜性弱碱的一种普遍补偿反应。因此，在某些长时间暴露的条件下，AMPHs和其他弱碱可通过导致囊泡酸化的补偿反应增强而非耗尽儿茶酚胺的囊泡释放。
