Milusheva E A, Dóda M, Baranyi M, Vizi E S
Institute of Physiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.
Neurochem Int. 1996 May-Jun;28(5-6):501-7. doi: 10.1016/0197-0186(95)00129-8.
Release of [3H]dopamine ([3H]DA) from rat striatal slices kept under hypoxic or/and glucose-free conditions was measured using a microvolume perfusion method. The corresponding changes in nucleotide content were determined by reverse-phase high-performance liquid chromatography (RPHPLC). The resting release of [3H]DA was not affected by hypoxia, but under glucose-free conditions massive [Ca2+]o-independent release of [3H]DA was observed. Hypoxia reduced the energy charge (E.C.) and the total purine content from 19.36 +/- 4.15 to 6.98 +/- 1.83 nmol/mg protein. Glucose deprivation by itself, or in combination with hypoxia, markedly reduced the levels of adenosine 5'-triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP). The E.C under glucose-free conditions was significantly reduced from 0.73 +/- 0.04 to 0.44 +/- 0.20. When the tissue was exposed to hypoxic and glucose-free conditions for 18 min the level of ATP was reduced to 3.15 +/- 0.11 nmol/mg protein. However, when the exposure time was 30 min the ATP level was further reduced to 1.11 +/- 0.37 nmol/mg protein. The resting release was enhanced in a [Ca2+]o-independent manner, but there was no release in response to stimulation, and tetrodotoxin did not affect the enhanced resting release, indicating that the release was not associated with axonal activity. Similarly, 50 microM ouabain, inhibitor of Na+/K(+)-activated ATPase, enhanced the release of [3H]DA at rest in a [Ca2+]o-independent manner. It seems very likely that the reduced ATP level under glucose-free conditions leads to an inhibition of the activity of Na+/K(+)-ATPase that results in reversal of the uptake processes and in [Ca2+]o-independent [3H]DA release from the axon terminals.
采用微量灌注法测定了在缺氧或/和无糖条件下保存的大鼠纹状体切片中[3H]多巴胺（[3H]DA）的释放。通过反相高效液相色谱法（RPHPLC）测定核苷酸含量的相应变化。缺氧不影响[3H]DA的静息释放，但在无糖条件下观察到大量不依赖细胞外钙离子（[Ca2+]o）的[3H]DA释放。缺氧使能荷（E.C.）和总嘌呤含量从19.36±4.15降至6.98±1.83 nmol/mg蛋白质。单独或与缺氧联合的葡萄糖剥夺显著降低了三磷酸腺苷（ATP）、二磷酸腺苷（ADP）和一磷酸腺苷（AMP）的水平。无糖条件下的能荷从0.73±0.04显著降至0.44±0.20。当组织暴露于缺氧和无糖条件18分钟时，ATP水平降至3.15±0.11 nmol/mg蛋白质。然而，当暴露时间为30分钟时，ATP水平进一步降至1.11±0.37 nmol/mg蛋白质。静息释放以不依赖[Ca2+]o的方式增强，但对刺激无释放反应，河豚毒素不影响增强的静息释放，表明该释放与轴突活动无关。同样，50μM哇巴因（Na+/K(+)-激活的ATP酶抑制剂）以不依赖[Ca2+]o的方式增强静息时[3H]DA的释放。很可能无糖条件下ATP水平的降低导致Na+/K(+)-ATP酶活性受到抑制，从而导致摄取过程逆转，并使轴突终末出现不依赖[Ca2+]o的[3H]DA释放。
