Kivatinitz S C, Miglio A, Ghidoni R
Department of Medical Chemistry and Biochemistry, Medical School, University of Milan, Italy.
Biochem J. 1991 Mar 1;274 ( Pt 2)(Pt 2):581-5. doi: 10.1042/bj2740581.
The fate of exogenous ganglioside GM1 labelled in the sphingosine moiety, [Sph-3H]GM1, administered as a pulse, in the isolated perfused rat liver was investigated. When a non-recirculating protocol was employed, the amount of radioactivity in the liver and perfusates was found to be dependent on the presence of BSA in the perfusion liquid and on the time elapsed after the administration of the ganglioside. When BSA was added to the perfusion liquid, less radioactivity was found in the liver and more in the perfusate at each time tested, for up to 1 h. The recovery of radioactivity in the perfusates followed a complex course which can be described by three pseudo-first-order kinetic constants. The constants, in order of decreasing velocity, are interpreted as: (a) the dilution of the labelled GM1 by the constant influx of perfusion liquid; (b) the washing off of GM1 loosely bound to the surface of liver cells; (c) the release of gangliosides from the liver. Process (b) was found to be faster in the presence of BSA, probably owing to the ability of BSA to bind gangliosides. The [Sph-3H]GM1 in the liver underwent metabolism, leading to the appearance of products of anabolic (GD1a, GD1b) and catabolic (GM2, GM3) origin; GD1a appeared before GM2 and GM3 but, at times longer than 10 min, GM2 and GM3 showed more radioactivity than GD1a. At a given time the distribution of the radioactivity in the perfusates was quite different from that of the liver. In fact, after 60 min GD1a was the only metabolite present in any amount, the other being GM3, the quantity of which was small. This indicates that the liver is able to release newly synthesized gangliosides quite specifically. When a recirculating protocol was used, there were more catabolites and less GD1a than with the non-recirculating protocol. A possible regulatory role of ganglioside re-internalization on their own metabolism in the liver is postulated.
研究了以脉冲形式给予的、鞘氨醇部分标记的外源性神经节苷脂GM1（[Sph-3H]GM1）在离体灌注大鼠肝脏中的命运。当采用非循环方案时，发现肝脏和灌注液中的放射性量取决于灌注液中牛血清白蛋白（BSA）的存在以及给予神经节苷脂后经过的时间。当向灌注液中添加BSA时，在每次测试时间（长达1小时），肝脏中发现的放射性较少，而灌注液中的放射性较多。灌注液中放射性的回收遵循一个复杂的过程，可用三个伪一级动力学常数来描述。按速度递减顺序，这些常数被解释为：（a）标记的GM1被灌注液的持续流入所稀释；（b）从肝细胞表面松散结合的GM1被洗脱；（c）神经节苷脂从肝脏释放。发现过程（b）在有BSA存在时更快，这可能是由于BSA结合神经节苷脂的能力。肝脏中的[Sph-3H]GM1发生了代谢，导致出现合成代谢（GD1a、GD1b）和分解代谢（GM2、GM3）来源的产物；GD1a比GM2和GM3出现得早，但在超过10分钟的时间里，GM2和GM3的放射性比GD1a更多。在给定时间，灌注液中放射性的分布与肝脏中的分布有很大不同。事实上，60分钟后，GD1a是唯一大量存在的代谢产物，另一种是GM3，其数量很少。这表明肝脏能够相当特异性地释放新合成的神经节苷脂。当使用循环方案时，与非循环方案相比，分解代谢产物更多，GD1a更少。推测神经节苷脂重新内化对其在肝脏中自身代谢可能具有调节作用。
