Calcium transport in epithelial cells of the intestine and kidney

The central role of 1α,25-dihydroxyvitamin D₃ in the regulation of calcium balance is well established. By increasing the absorption of calcium in the intestine and the reabsorption of filtered calcium in the kidney tubule, the hormone maintains an appropriate calcium balance. The cellular mechanisms that underlie the increase in calcium transport in epithelial cells in response to 1α,25-dihydroxyvitamin D₃ are beginning to be defined. These events include an increase in the movement of calcium across the apical membrane of the cell, an increase in the movement of calcium across the cell, and an increase in the extrusion of calcium at the basolateral portion of the cell. In this Prospects article, I will discuss the nature of the various processes and proteins involved in transcellular calcium movement, and I will attempt to highlight various future areas of research.     

Phosphofructokinase D from the epithelial cells of rat small intestine.

Phosphofructokinase from the epithelial cells of rat small intestine was characterized with respect to isoenzyme type in a comparison of its properties with those of the skeletal-muscle, brain and major liver isoenzymes by using five different techniques, namely electrophoresis on cellulose acetate and in polyacrylamide gels, chromatography on DEAE-cellulose, (NH4)2SO4 precipitation and immunotitration. When precautions were taken to inhibit the formation of active proteolytic artifacts by the action of endogenous proteinases, each technique revealed that rat intestinal mucosa contains only a single form of phosphofructokinase. The mucosal isoenzyme was found to be very similar to, although not identical with, the major liver isoenzyme and to be quite distinct from the skeletal-muscle isoenzyme when studied by the techniques of cellulose acetate electrophoresis, chromatography on DEAE-cellulose and immunotitration, whereas the converse was true when studied by the techniques of (NH4)2SO4 precipitation and polyacrylamide-gel electrophoresis. The mucosal isoenzyme was distinct from the brain isoenzyme when studied by each of the five techniques. Tsai & Kemp [(1973) J. Biol. Chem. 248, 785-792] reported that animal tissues contain three principal isoenzymes of phosphofructokinase, type A found as the sole isoenzyme in skeletal muscle, type B found as the major isoenzyme in liver and type C found as a significant isoenzyme in brain. Phosphofructokinase from mucosa is distinct from each of these isoenzymes. Following the nomenclature of Tsai & Kemp (1973), the isoenzyme from the mucosa of rat intestinal epithelial cells is designated phosphofructokinase D. The mucosal and liver isoenzymes behave so similarly with respect to their charge and immunological characteristics, on which the typing of isoenzymes is conventionally based, that it is likely that some tissues reported to contain the liver isoenzyme contain instead the mucosal isoenzyme.     

小肠上皮分泌细胞特性的组织学观察

目的寻找一种可以替代人体消化管的动物标本,并通过特殊染色方法,使得小肠上皮分泌细胞的形态特征能够明显地显示出来。方法随机采集成年猫小肠的新鲜标本,经Bouin液灌注固定24h后,石蜡包埋切片脱蜡入水。分别采用Gomori染色法、PAS反应、Gomori＋PAS反应、阿利新蓝（alcian blue,AB）染色法、AB＋PAS反应、HE染色法和苏木精-焰红染色法进行染色。结果在各种染色的切片标本上,能够观察到杯状细胞的形态、分布和染色特性以及肠内分泌细胞的特点,并发现在它们之间还存在一种绿色颗粒细胞和嗜酸性颗粒细胞。结论通过特殊染色可以肯定猫的小肠杯状细胞合成的是中性粘蛋白和酸性粘蛋白;绿色颗粒细胞为未成熟杯状细胞;嗜酸性颗粒细胞为Paneth细胞,其特点是单个分散分布。肠内分泌细胞与周围其他上皮细胞的染色对比明显而容易识别。     

Cell cycle time and rate of entry of cells into mitosis in the small intestine of young rats

Cell cycle time (T(C)) and the rate of entry of cells into mitosis (r(M)) in the jejunum and duodenum of young rats were investigated using the stathmokinetic method. The cell cycle times in the jejunum were 24.3 and 28.3 h in light and dark periods, respectively. Cell cycle times in the duodenum were 17.1 and 21.5 h in light and dark periods, respectively. Rates of entry of cells into mitosis in the jejunum were 1.2 and 1.1 cells/cell/h in light and dark periods and rates of entry of cells into mitosis in the duodenum were 1.4 and 1.8 cells/cell/h in light and dark periods, respectively. Although these changes to cell cycle time values are not statistically significant, the variation between the two periods should be considered in relation to its possible biological effects.     

Catalase particles in the epithelial cells of the guinea-pig small intestine

Synopsis Purified preparations of epithelial cells have been made from the guinea-pig small intestine. Homogenates of these preparations have been analysed by centrifugation in a zonal rotor. The results confirm the presence of lysosomes in these cells and indicate the existence of catalase particles which equilibrate in a sucrose gradient at a density of between 1.21 and 1.23 and which have a different distribution from other subcellular particles except lysosomes. Injection of Triton WR-1339 into fasting animals enables the separation of lysosomes and catalase particles.     

Two novel decaglycosylceramides with a blood group A-active tetrasaccharide repeat in the epithelial cells of the small intestine of inbred rats.

A novel type of blood group A-active glycosphingo-lipid was isolated from the epithelial cells of the small intestine of one strain of inbred rats. Electron-impact mass spectrometry of the permethylated and LiAlH4-reduced glycolipid indicated that it is a decaglycosylceramide with a branched oligosaccharide chain. Methylation analysis, gas chromatography-mass spectroscopy of the partially methylated alditol acetates, sequential degradation by exoglycosidases and characterization of the reaction products by TLC immunostaining with appropriate anti-A and anti-H antibodies, and 1H NMR spectrometry resulted in the characterization of a decaglycosylceramide with two variants in a 7/3 ratio. It was termed AA-10. [formula: see text] The major variant has only type 1 chains, whereas the minor one has type 2 chain in the C6-linked branch. This is a novel type of glycolipid with a blood group A-active tetrasaccharide repeat. Genetic analysis demonstrated that AA-10 is inherited as an autosomal dominant trait.     

Lipoproteins of rat small intestine epithelial cells in D-hypovitaminosis

Chemical composition of lipoproteins has been studied in intestinal epitheliocytes of rats in normalcy and under D-hypovitaminosis. It is found that D-hypovitaminosis induces changes in the lipid and protein composition of lipoproteins. It is supposed that disturbances in biosynthesis of the lipoprotein components and their transport may be possible reasons of such changes.     

The isolation and characterization of phosphofructokinase from the epithelial cells of rat small intestine.

1. Only a single phosphofructokinase isoenzyme is present in the mucosa of rat small intestine. 2. Mucosal phosphofructokinase was purified to yield a homogeneous preparation of specific activity 175 units/mg of protein. 3. The native enzyme is a tetramer, with monomer Mr 84 500 +/- 5000. 4. The native enzyme may be degraded by the action of endogenous proteinases to give two products with the same specific activity as the native enzyme: degradation occurs in the order native enzyme leads to proteolytic product 1 leads to proteolytic product 2. 5. Proteolytic product 1 has a greater mobility in cellulose acetate electrophoresis at pH8 and binds more strongly to DEAE-cellulose than does native enzyme; the converse is true for proteolytic product 2. 6. Proteolytic product 1 is a tetramer with a monomer Mr about 74 300; proteolytic product 2 is also a tetramer. 7. Native enzyme can only be prepared in the presence of proteinase inhibitors; partial purifications based on simple fractionation of crude mucosal extracts in the absence of proteinases inhibitors contain proteolytic product 2 as the main component and proteolytic product 1 together with little native enzyme. 8. Purified native mucosal phosphofructokinase displayed little co-operativity with respect to fructose 6-phosphate at pH 7.0 and was only weakly inhibited by ATP.     

Diet, mucosal architecture and epithelial cell production in the small intestine of specified-pathogen-free and conventional rats.

Upper jejunum and terminal ileum were examined in specified-pathogen-free (SPF), conventional and conventional after SPF rearing (ex-SPF) rats. The effect of 2 differential diets on the last 2 groups was examined. Ex-SPF rats had taller villi and deeper crypts than SPF rats, but similar crypt to villus ratios and cell production rates. Ex-SPF rats had similar crypt depth and jejunal villus height to conventional rats on the same diet, but taller ileal villi and a lower cell production rate. Even after 6-8 weeks, in a conventional environment, ex-SPF rat intestine was still not identical with conventional rat intestine. Diet had a significant effect on mucosal architecture, and a smaller effect on cell production rate. It is concluded that diet, microbiological status of colony of origin, and environment after weaning, can all affect mucosal architecture and epithelial cell production, and should be properly controlled in experimental studies.     

Antigenic translocation of carcinoembryonic antigen in large intestine epithelial cells

By an indirect Coons test, a carcinoembryonic antigen (CEA) localization was studied in cells of colon mucosa at various stages of human embryonic development, polyps, and in cases of non-tumoral changes. Laboratory investigations have shown that there are several variants of CEA localization in embryogeny, precancerous tissue, and in cells with inflammatory changes. A comparison of the obtained data and forms of antigenic translocation in malignant tissue leads to a conclusion that the antigenic translocation phenomenon is of biological nature, reflecting the degree of changes in the inner structure of cells under various conditions of existence.     

L-MBP is expressed in epithelial cells of mouse small intestine

The mannan-binding proteins (L-MBP and S-MBP, also denoted MBL-C and MBL-A), mainly produced in liver and existing in liver and serum, play important roles in the innate immunity against a variety of pathogens. Total RNA from mouse tissues were screened for MBP mRNA by RT-PCR. In addition to liver, S-MBP mRNA was detected in lung, kidney, and testis, and L-MBP mRNA was detected in kidney, thymus, and small intestine. Quantitative RT-PCR revealed that the small intestine is a predominant site of extrahepatic expression of L-MBP. Western blotting with polyclonal Abs against rat L-MBP demonstrated this protein in Triton X-100 extracts of the small intestine obtained from mice that had undergone systemic perfusion. Immunohistochemical staining with an mAb against mouse L-MBP and in situ hybridization revealed that L-MBP is selectively expressed in some villous epithelial cells of the small intestine. These findings suggest that L-MBP plays a role in mucosal innate immunity.     

Phosphodiesterase II in epithelial cells from guinea-pig and rat small intestine

Phosphodiesterase II activity was determined by using a synthetic substrate, the 2,4-dinitrophenyl ester of thymidine 3'-phosphate. The enzyme activity was determined in fractions obtained by differential centrifugation of homogenates of epithelial cells from the small intestinal mucosa of guinea pigs and rats. In guinea-pig preparations phosphodiesterase II occurred with highest specific activity in those fractions rich in succinate dehydrogenase and acid phosphatase. A lysosomal location for the guinea-pig enzyme was indicated by its structure-linked latency and by its association with particles that under-went a characteristic decrease in equilibrium density when Triton WR-1339 was injected into the animals. With rat preparations a much greater proportion of the phosphodiesterase II activity was found in the soluble fraction after ultracentrifugation. The rat enzyme exhibited a lower degree of latency and administration of Triton WR-1339 had no effect. The rat enzyme further differed from that of the guinea pig in other respects; it was more labile at 60 degrees C, it exhibited a lower pH optimum and it had a higher molecular weight as determined by gel-filtration chromatography.