Mishkin S, Yalovsky M, Kessler J I
J Lipid Res. 1972 Mar;13(2):155-68.
The stages of uptake and incorporation of micellar palmitic acid by hamster proximal intestinal mucosa were investigated by incubation of everted sacs at 4 degrees C and 37 degrees C for 2, 5, 10, and 15 min in a micellar solution (10 micro moles of [1-(14)C]palmitic acid, 10 micro moles of monoolein, and 100 micro moles of sodium taurodeoxycholate) and subsequent serial rinsing of the sacs in ice-cold solutions as follows: one 20-sec rinse in unlabeled micellar solution, five 1-min rinses in Krebs-Ringer buffer (0.15 m, pH 6.3), and ten 2-min rinses in 2.5% albumin solution. The fatty acid-solubilizing capacity of all the rinsing solutions was always in excess of the amounts of radioactive palmitic acid released during each rinse. Radioactivity was determined in the tissue homogenates, rinsing solutions, and serosal fluids. The results indicate that a significant proportion of radioactive palmitic acid taken up by the sacs during the short incubation was released into the rinsing solutions. Rinsing in Krebs-Ringer buffer resulted in release of 15.5 +/- 2.4% of the labeled fatty acid, and this fraction was independent of the temperature of incubation. In contrast, the amounts of palmitic acid released in albumin were significantly greater and were markedly dependent on the temperature of incubation; a total of 48.6 +/- 7.0% and 26.3 +/- 5.1% was released from sacs incubated at 4 degrees C and 37 degrees C, respectively. While the proportion of radioactive palmitic acid in the free fatty acid fraction of the tissue after the rinsing sequence remained reasonably constant regardless of the temperature and duration of incubation, the radioactivity of the esterified palmitic acid in the tissue was much greater in the sacs incubated at 37 degrees C and tended to increase linearly up to 10 min of incubation. A highly significant inverse relationship was found between the fraction of radioactive palmitic acid released by rinsing in albumin and the fraction of the label in the tissue esterified fatty acids. The results suggest that the initial uptake of micellar fatty acid by intestinal mucosa may involve reversible binding to superficial sites with at least two strengths of binding: a weak, temperature-independent binding which could be easily dissociated by rinsing in Krebs-Ringer buffer, and a stronger, temperature-dependent binding which could be dissociated by rinsing in albumin, but not in Krebs-Ringer buffer. Analogous binding of micellar palmitic acid occurred in a brush border preparation of proximal intestine which was devoid of any fatty acid esterifying activity. This suggested that the reversible binding of fatty acid by the intestinal mucosa may be a property of its superficial components, namely the glycocalyx or microvillous membranes, and that it may be independent of the esterifying capacity of the tissue.
通过在4℃和37℃下，将外翻肠囊在胶束溶液（10微摩尔[1-(14)C]棕榈酸、10微摩尔单油酸甘油酯和100微摩尔牛磺脱氧胆酸钠）中孵育2、5、10和15分钟，随后按如下方式在冰冷溶液中对肠囊进行连续冲洗，研究了仓鼠近端肠黏膜对胶束棕榈酸的摄取和掺入阶段：在未标记的胶束溶液中冲洗20秒，在 Krebs-Ringer缓冲液（0.15 m，pH 6.3）中冲洗5次，每次1分钟，在2.5%白蛋白溶液中冲洗10次，每次2分钟。所有冲洗溶液的脂肪酸溶解能力始终超过每次冲洗过程中释放的放射性棕榈酸的量。测定了组织匀浆、冲洗溶液和浆膜液中的放射性。结果表明，在短时间孵育期间，肠囊摄取的大量放射性棕榈酸释放到冲洗溶液中。在Krebs-Ringer缓冲液中冲洗导致15.5±2.4%的标记脂肪酸释放，且该部分与孵育温度无关。相比之下，在白蛋白中释放的棕榈酸量显著更大，且明显依赖于孵育温度；在4℃和37℃孵育的肠囊中，分别有48.6±7.0%和26.3±5.1%的棕榈酸被释放。尽管冲洗序列后组织游离脂肪酸部分中放射性棕榈酸的比例无论孵育温度和持续时间如何都保持相当恒定，但在37℃孵育的肠囊中，组织中酯化棕榈酸的放射性要高得多，并且在孵育10分钟内趋于线性增加。在白蛋白中冲洗释放的放射性棕榈酸部分与组织酯化脂肪酸中的标记部分之间发现了高度显著的负相关关系。结果表明，肠黏膜对胶束脂肪酸的初始摄取可能涉及与表面位点的可逆结合，至少有两种结合强度：一种是弱的、与温度无关的结合，可通过在Krebs-Ringer缓冲液中冲洗轻易解离；另一种是较强的、与温度有关的结合，可通过在白蛋白中冲洗解离，但不能在Krebs-Ringer缓冲液中解离。在近端肠的刷状缘制剂中发生了胶束棕榈酸的类似结合，该制剂没有任何脂肪酸酯化活性。这表明肠黏膜对脂肪酸的可逆结合可能是其表面成分即糖萼或微绒毛膜的特性，并且可能与组织的酯化能力无关。
