Mac M, Nehlig A, Nałecz M J, Nałecz K A
Department of Molecular and Cellular Neurobiology, Nencki Institute of Experimental Biology, Pasteur Street 3, Warsaw, 02-093, Poland.
Arch Biochem Biophys. 2000 Apr 15;376(2):347-53. doi: 10.1006/abbi.2000.1724.
Transport of alpha-ketoisocaproic acid (KIC), the product of leucine transamination, was studied in the cerebral cortex cells isolated from the adult rat brain. The process of [(14)C]KIC accumulation was followed in the presence of aminooxyacetate, an inhibitor of transaminases. Accumulation of KIC was not affected by Na(+) replacement, its initial velocity was observed to be higher upon lowering of external pH. Addition of KIC promoted acidification of cytoplasmic pH, monitored with 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. The detected inhibition of KIC accumulation by alpha-cyano-4(OH)cinnamate pointed to an involvement of one of monocarboxylate transporters (MCT), although 4,4'-diisothiocyano-2,2'-stilbenedisulphonate was without effect. Accumulation of KIC was inhibited by lactate; the effect of pyruvate was detected to be much weaker. Other branched-chain alpha-ketoacids (ketoisovalerate, keto-methylvalerate), as well as beta-hydroxybutyrate and valproate decreased the transport of KIC by 30, 60, and 80%, respectively. The observed characteristics of KIC accumulation in the cortical neurons indicate an involvement of one of the MCT transporters. A crucial role of SH group(s) in the process of KIC accumulation, excluding MCT2, indicates the MCT1, although an involvement of another isoform of MCT in the process of KIC transport in neurons from cerebral cortex of adult brain has not been definitely excluded.
在从成年大鼠脑中分离出的大脑皮层细胞中，对亮氨酸转氨作用的产物α-酮异己酸（KIC）的转运进行了研究。在转氨酶抑制剂氨氧基乙酸存在的情况下，追踪了[¹⁴C]KIC的积累过程。KIC的积累不受Na⁺替代的影响，在降低外部pH值时观察到其初始速度较高。添加KIC会促进细胞质pH值的酸化，用2'7'-双（羧乙基）-5（6）-羧基荧光素进行监测。α-氰基-4（OH）肉桂酸对KIC积累的检测抑制表明一元羧酸转运体（MCT）之一参与其中，尽管4,4'-二异硫氰酸-2,2'-二苯乙烯二磺酸盐没有效果。KIC的积累受到乳酸的抑制；检测到丙酮酸的作用要弱得多。其他支链α-酮酸（酮异戊酸、酮甲基戊酸）以及β-羟基丁酸和丙戊酸分别使KIC的转运降低了30%、60%和80%。在皮质神经元中观察到的KIC积累特征表明MCT转运体之一参与其中。SH基团在KIC积累过程中的关键作用（不包括MCT2）表明是MCT1，尽管尚未明确排除成年大脑皮层神经元中KIC转运过程中另一种MCT同工型的参与。
