Gromova L V, Gruzdkov A A
Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg.
Gen Physiol Biophys. 1999 Jun;18(2):209-24.
In order to throw light on the mechanisms responsible for the enzyme-dependent absorption of disaccharides membrane hydrolysis of maltose and trehalose and the absorption of glucose (free and that derived from disaccharides) were studied in isolated loops (20 cm) of the rat small intestine in chronic experiments. The rates of glucose absorption were 0.26-0.81 micromol x min(-1) x cm(-1) when the loop was perfused with a 12.5 to 75.0 mmol/l free glucose solution, which is only insignificantly higher than the rates observed during perfusion with equivalent maltose solutions. The coupling coefficient (the ratio of glucose absorption rate to the rate of disaccharide hydrolysis) decreased from 0.90 to 0.60 with the increasing maltose concentrations in the infusate from 6.25 to 37.5 mmol/l, but remained unchanged (approximately 0.95) within the same range of trehalose concentrations. The permeability of the pre-epithelial barrier was equivalent to that of unstirred water layer of less than 40 microm thickness. Fluid absorption was within the range of 0.73-2.55 microl x min(-1) x cm(-1), and it showed a correlation with the rates of glucose absorption. The results agree with a model developed on the assumption that free glucose and that released from disaccharides share the same membrane transporters. It could be concluded that a close coupling of disaccharide hydrolysis with derived glucose absorption in chronic experiments is achieved mainly due to a high activity of glucose transporters, which are presumably not associated with membrane disaccharidases. The transcellular active transport is a predominant mechanism of disaccharide-derived glucose absorption under conditions close to physiological.
为了阐明双糖酶依赖性吸收的机制，在慢性实验中，对大鼠小肠分离肠袢（20厘米）中麦芽糖和海藻糖的膜水解以及葡萄糖（游离的和双糖衍生的）吸收进行了研究。当肠袢用12.5至75.0毫摩尔/升的游离葡萄糖溶液灌注时，葡萄糖吸收速率为0.26 - 0.81微摩尔×分钟⁻¹×厘米⁻¹，这仅比用等量麦芽糖溶液灌注时观察到的速率略高。随着灌注液中麦芽糖浓度从6.25毫摩尔/升增加到37.5毫摩尔/升，偶联系数（葡萄糖吸收速率与双糖水解速率之比）从0.90降至0.60，但在相同海藻糖浓度范围内保持不变（约0.95）。上皮前屏障的通透性相当于厚度小于40微米的未搅拌水层的通透性。液体吸收范围为0.73 - 2.55微升×分钟⁻¹×厘米⁻¹，并且与葡萄糖吸收速率相关。结果与基于游离葡萄糖和双糖释放的葡萄糖共享相同膜转运体这一假设建立的模型一致。可以得出结论，在慢性实验中，双糖水解与衍生葡萄糖吸收的紧密偶联主要是由于葡萄糖转运体的高活性，这些转运体可能与膜双糖酶无关。在接近生理条件下，跨细胞主动转运是双糖衍生葡萄糖吸收的主要机制。
