Aschner M, Du Y L, Gannon M, Kimelberg H K
Department of Pharmacology and Toxicology, Albany Medical College, NY 12208.
Brain Res. 1993 Feb 5;602(2):181-6. doi: 10.1016/0006-8993(93)90680-l.
To determine whether methylmercury (MeHg) has the potential to interfere with homeostatic functions in neonatal rat cortical primary astrocyte cultures, the effects of MeHg on the uptake and efflux of both L-glutamate and D-aspartate were examined. Uptake of both of these excitatory amino acids (EAAs) was significantly (P < 0.05) reduced in the presence of MeHg concentrations as low as 10(-5) M. Efflux of both glutamate and aspartate from preloaded astrocytes was also increased by MeHg in a dose- and time-dependent fashion. Since in our earlier studies we had found that MeHg causes dose-dependent astrocytic swelling, which could have been the mechanism of the increased efflux, we examined whether blockage of conductive ion fluxes, which have been implicated in astrocytic swelling, could reverse the MeHg-induced increase in L-glutamate and D-aspartate efflux. Three compounds which inhibit the hypotonic-media-induced efflux of EAA, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS), L-644,711 (a derivative of ethacrynic acid) and furosemide were tested at their maximal concentrations for their ability to reverse MeHg-induced EAA efflux. Only furosemide (5 mM) could sustain the reversal for the entire 120 min duration of the efflux measurement. Since hypotonic-media swelling-induced release of EAAs is inhibited by these anion inhibitors (in the following rank order: L-644,711 > SITS > furosemide), we conclude that different mechanisms account for EAA release from primary astrocyte cultures during MeHg exposure as compared to hypotonic media-induced efflux.
为了确定甲基汞（MeHg）是否有可能干扰新生大鼠皮质原代星形胶质细胞培养物中的稳态功能，研究了MeHg对L-谷氨酸和D-天冬氨酸摄取及外排的影响。在低至10(-5) M的MeHg浓度存在下，这两种兴奋性氨基酸（EAAs）的摄取均显著（P < 0.05）降低。MeHg还以剂量和时间依赖性方式增加了来自预负载星形胶质细胞的谷氨酸和天冬氨酸的外排。由于在我们早期的研究中发现MeHg会导致剂量依赖性的星形胶质细胞肿胀，这可能是外排增加的机制，因此我们研究了与星形胶质细胞肿胀有关的传导性离子通量的阻断是否能逆转MeHg诱导的L-谷氨酸和D-天冬氨酸外排增加。测试了三种抑制低渗介质诱导的EAA外排的化合物，4-乙酰氨基-4'-异硫氰酸基芪-2,2'-二磺酸（SITS）、L-644,711（依他尼酸的衍生物）和呋塞米，以它们的最大浓度来测试其逆转MeHg诱导的EAA外排的能力。只有呋塞米（5 mM）能够在整个120分钟的外排测量期间维持这种逆转。由于这些阴离子抑制剂（以下排序：L-644,711 > SITS > 呋塞米）抑制了低渗介质肿胀诱导的EAAs释放，我们得出结论，与低渗介质诱导的外排相比，MeHg暴露期间原代星形胶质细胞培养物中EAA释放的机制不同。
