Jones S R, Garris P A, Wightman R M
Department of Chemistry and Curriculum in Neurobiology, University of North Carolina, Chapel Hill, USA.
J Pharmacol Exp Ther. 1995 Jul;274(1):396-403.
The effects of cocaine and nomifensine on the uptake of dopamine have been compared in the caudate-putamen and nucleus accumbens of rat brain slices. Electrical stimulation of brain slices was used to evoke dopamine efflux and the changes in dopamine concentration in the extracellular fluid were monitored with fast-scan cyclic voltammetry with Nafion-coated, carbon-fiber electrodes. The disappearance of extracellular dopamine after the stimulation fit Michaelis-Menten kinetics in both regions. Cocaine and nomifensine were found to competitively inhibit dopamine uptake in both regions. The competitive mechanism of action was apparent in the primary data because the initial uptake rates were unchanged by low doses of inhibitor, but dopamine uptake was slowed at concentrations near the Km value. In both regions, the apparent Km value increased with higher concentrations of cocaine (0.01-60 microM) or nomifensine (0.01-30 microM) in the perfusion buffer. The apparent Km values were used to obtain inhibition constants (Ki values) for the uptake inhibitors in each region. This analysis showed that cocaine had a Ki of 0.29 microM in both regions. Nomifensine, however, had a significantly higher potency in the caudate-putamen (Ki = 0.09 microM) than in the nucleus accumbens (Ki = 0.21 microM). These results show that there are differential effects of uptake inhibitors in different brain regions, and suggest that the dopamine transporter exhibits cell-specific regulation.
已在大鼠脑片的尾状核-壳核和伏隔核中比较了可卡因和诺米芬辛对多巴胺摄取的影响。使用脑片电刺激来诱发多巴胺外流，并使用涂有Nafion的碳纤维电极通过快速扫描循环伏安法监测细胞外液中多巴胺浓度的变化。刺激后细胞外多巴胺的消失在两个区域均符合米氏动力学。发现可卡因和诺米芬辛在两个区域均竞争性抑制多巴胺摄取。在原始数据中，竞争作用机制很明显，因为低剂量抑制剂不会改变初始摄取速率，但在接近Km值的浓度下多巴胺摄取会减慢。在两个区域中，灌注缓冲液中较高浓度的可卡因（0.01 - 60 microM）或诺米芬辛（0.01 - 30 microM）会使表观Km值增加。表观Km值用于获得每个区域中摄取抑制剂的抑制常数（Ki值）。该分析表明，可卡因在两个区域中的Ki均为0.29 microM。然而，诺米芬辛在尾状核-壳核（Ki = 0.09 microM）中的效力明显高于伏隔核（Ki = 0.21 microM）。这些结果表明，摄取抑制剂在不同脑区有不同作用，提示多巴胺转运体表现出细胞特异性调节。
