Munck L K
Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark.
Am J Physiol. 1993 Nov;265(5 Pt 1):G979-86. doi: 10.1152/ajpgi.1993.265.5.G979.
This article examines the nature of the Cl- dependence of the rabbit intestinal imino acid carrier using 2-methyl-aminoisobutyric acid (MeAIB) as substrate for measuring influx across the luminal membrane of rabbit distal ileum. Reduction of mucosal Cl- concentration from 140 to 6 mM successively increased the concentration at which MeAIB influx is half-maximal from 3.6 +/- 0.2 (SD) to 21.0 +/- 3.7 mM. Maximal influx of MeAIB was unchanged. Measured at 70 mM Cl-, MeAIB induced a Cl- influx across the brush-border membrane (delta JClmc) of 5.01 +/- 0.65 mumol.cm-2 x h-1 (SE, n = 16; 45%), and an identical Cl(-)-independent influx of leucine induced a delta JClmc of 1.82 +/- 0.52 mumol.cm-2 x h-1 (SE, n = 12; 16%) (P < 0.001). At 24 mM Cl-, delta JClmc induced by leucine did not differ significantly from zero, whereas the effect of MeAIB was maintained. The ratio between Na+ influx across brush-border membrane (delta JNamc) and the Na(+)-dependent flux measured at 140 mM Cl- was 2.4 +/- 0.7 (n = 8) for MeAIB, 1.4 +/- 0.4 (n = 10) for leucine, and 1.1 +/- 0.2 (n = 13) for D-glucose. The Hill coefficient of Na+ activation (+/- SD) in distal ileum was 0.82 +/- 0.19 for leucine and 1.14 +/- 0.03 for D-glucose. A Hill coefficient of 1.60 +/- 0.05 was obtained for D-glucose in the jejunum. Concentrations of MeAIB and D-glucose, chosen to given equal delta JNamc, induced a 40 and 21% increment of JClmc (P < 0.05), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
本文以2-甲基氨基异丁酸（MeAIB）作为底物，用于测量兔回肠远端肠腔膜的流入量，以此研究兔肠道亚氨基酸载体对氯离子的依赖性本质。将黏膜氯离子浓度从140 mM降至6 mM，依次使MeAIB流入量达到最大值一半时的浓度从3.6±0.2（标准差）mM增加至21.0±3.7 mM。MeAIB的最大流入量未发生变化。在70 mM氯离子浓度下测量时，MeAIB诱导穿过刷状缘膜的氯离子流入量（δJClmc）为5.01±0.65 μmol·cm⁻²·h⁻¹（标准误，n = 16；45%），而相同的不依赖氯离子的亮氨酸流入量诱导的δJClmc为1.82±0.52 μmol·cm⁻²·h⁻¹（标准误，n = 12；16%）（P < 0.001）。在24 mM氯离子浓度下，亮氨酸诱导的δJClmc与零无显著差异，而MeAIB的作用得以维持。对于MeAIB，穿过刷状缘膜的钠离子流入量（δJNamc）与在140 mM氯离子浓度下测量的依赖钠离子通量的比值为2.4±0.7（n = 8），亮氨酸为1.4±0.4（n = 10），D-葡萄糖为1.1±0.2（n = 13）。回肠中亮氨酸的钠离子激活希尔系数（±标准差）为0.82±0.19，D-葡萄糖为1.14±0.03。空肠中D-葡萄糖的希尔系数为1.60±0.05。选择使δJNamc相等的MeAIB和D-葡萄糖浓度，分别使JClmc增加了40%和21%（P < 0.05）。（摘要截取自250字）
