Kanner B I, Sharon I
Biochemistry. 1978 Sep 19;17(19):3949-53. doi: 10.1021/bi00612a011.
Membrane vesicles, isolated after osmotic shock of synaptosomal rat brain fractions, actively accumulate L-glutamate. This process requires the presence of external sodium ions and internal potassium ions and is driven by artifically imposed ion gradients as the sole energy source. Either an Na+ gradient (out is greater than in) or a K+ gradient (in is greater than out) or both can be utilized to concentrate L-glutamate inside the vesicles. Transport is enhanced by valinomycin or by external thiocyanate ions and is about 50% inhibited by the proton ionophore carbonyl cyanide m-chlorophenylhydrazone. This transport thus appears to be stimulated by a membrane potential (interior negative). The glutamate transporter, the Km of which has been determined to be 3 micrometer, is specific for L-glutamate. The transport process is unaffected by ouabain but is strongly inhibited by p-hydroxymercuribenzoate as well as by nigericin, which collapses the energizing ion gradients across this membrane. Unlike the sodium dependent, but potassium independent active accumulation of gamma-aminobutyric acid in these vesicles (Kanner, B.I. (1978) Biochemistry 17, 1207) active L-glutamate uptake is not dependent on the presence of small monovalent anions in the external medium. The results provide direct evidence for Na+-coupled electrogenic active L-glutamate transport by rat brain membrane vesicles. The dependence on internal potassium ions is discussed.
通过对大鼠脑突触体部分进行渗透压休克后分离得到的膜囊泡能够主动积累L-谷氨酸。这一过程需要细胞外钠离子和细胞内钾离子的存在，并且由人工施加的离子梯度作为唯一能量来源驱动。无论是Na⁺梯度（细胞外大于细胞内）还是K⁺梯度（细胞内大于细胞外）或者两者都可以用于在囊泡内浓缩L-谷氨酸。缬氨霉素或细胞外硫氰酸根离子可增强转运，而质子离子载体羰基氰化物间氯苯腙可抑制约50%的转运。因此，这种转运似乎受到膜电位（膜内为负）的刺激。谷氨酸转运体的Km值已确定为3微米，对L-谷氨酸具有特异性。转运过程不受哇巴因影响，但受到对羟基汞苯甲酸以及尼日利亚菌素的强烈抑制，后者会破坏跨膜的供能离子梯度。与这些囊泡中γ-氨基丁酸的钠依赖性但钾非依赖性主动积累不同（Kanner, B.I. (1978) Biochemistry 17, 1207），L-谷氨酸的主动摄取不依赖于细胞外介质中小单价阴离子的存在。这些结果为大鼠脑膜囊泡中Na⁺偶联的电生性L-谷氨酸转运提供了直接证据。文中还讨论了对细胞内钾离子的依赖性。
