Identification and comparison of bile acid-binding polypeptides in ileal basolateral membrane

Bile acid-binding polypeptides were examined using basolateral membrane vesicles and enterocytes isolated from rat ileum. The uptake of a photolabile taurocholate derivative, (7,7,-azo-3 alpha,12 alpha-dihydroxy-5 beta[3 beta-3H]cholan-24-oyl)-2- aminoethanesulfonate,7,7-azo-TC, in ileal vesicles preloaded with paraaminohippurate (PAH) was stimulated with respect to uptake in unpreloaded vesicles. The PAH-transstimulated uptake of 7,7-azo-TC was inhibited by taurocholate and vice versa. Irradiation of membrane vesicles in the presence of 7,7-azo-TC irreversibly inhibited PAH-transstimulated taurocholate uptake. Photoaffinity labeling of basolateral membrane vesicles directly with [3H] 7,7-azo-TC and separation of proteins by SDS-PAGE revealed incorporation of radioactivity into several polypeptides. Photoaffinity labeling of vesicles in the presence of taurocholate inhibited the labeling of 54,000 and 59,000 mol. wt. polypeptides. The efflux of taurocholate from ileal enterocytes was cis-inhibited by 7,7-azo-TC and transstimulated by PAH. Irradiation of enterocytes in the presence of 7,7-azo-TC inhibited taurocholate efflux greater than the presence of 7,7-azo-TC in the dark. When enterocytes that were irradiated in the presence of [3H] 7,7-azo-TC were fractionated and the resultant basolateral membrane fraction was subjected to SDS-PAGE, incorporation of radioactivity into the 54,000 and 59,000 mol. wt. polypeptides was seen. In contrast, when the brush-border membrane fraction was subjected to SDS-PAGE, greatest incorporation of radioactivity was seen in the previously described 99,000 mol. wt. polypeptide. These studies suggest that 7,7-azo-TC shared transporters with natural bile acid and identified polypeptides that may be involved in bile acid transport across the basolateral membrane and differ from that seen in the brush-border membrane of the ileal epithelial cell.

The chemotactic peptide N-formyl methionyl-leucyl-phenylalanine increases mucosal permeability in the distal ileum of the rat

Activation of granulocytes within the lamina propria by luminally derived bacterial products may represent an important mechanism in the pathogenesis of inflammatory bowel disease. The objective of this study was to determine the effects of luminal perfusion with N-formyl methionyl-leucyl-phenylalanine (FMLP), a bacterial product that attracts and activates granulocytes, on mucosal permeability in different regions of the rat small intestine and colon. Mucosal permeability was measured using blood-to-lumen clearance of 51Cr-ethylenediamine-tetraacetate during luminal perfusion with FMLP (10(-3) to 10(-8) M) dissolved in Tyrode's solution. Of the bowel segments studied, mucosal permeability was significantly increased by FMLP only in the distal 10 cm of ileum. The minimal FMLP concentration required to increase mucosal permeability was 10(-6) M. The increased mucosal permeability induced by FMLP could be prevented by depletion of circulating granulocytes with antineutrophil serum. The greater sensitivity of the distal ileum to FMLP did not correlate with a higher tissue myeloperoxidase activity, but it was associated with a higher basal ethylenediaminetetraacetate clearance. These observations indicate that a high basal mucosal permeability to solutes the size of FMLP (5-6 A radius), rather than a greater number of resident granulocytes in the lamina propria, predisposes the terminal ileum to the inflammatory actions of FMLP.

Discrepancy between effects of cholera toxin on net fluid movement and cAMP levels in rat jejunum, ileum, and colon

Regional differences in the response to cholera toxin were evaluated in rat jejunum, ileum, and colon in vivo. Ligated intestinal loops were exposed to a supramaximal concentration of cholera toxin for 5 hr, and net fluid transport, adenosine 3',5'-monophosphate (cAMP) concentrations, and adenylate cyclase and phosphodiesterase activities of mucosal homogenates were determined. The fluid transport response and the specific activities of adenylate cyclase (with and without cholera toxin) and phosphodiesterase declined progressively from the jejunum to the colon. In contrast, cAMP concentrations (with and without cholera toxin) were lowest in the jejunum and highest in the colon. These results demonstrate that cAMP concentrations of the total mucosal homogenate do not parallel cholera toxin-induced fluid secretion in the three intestinal segments. Rather, the activities of adenylate cyclase and phosphodiesterase suggest a relation between fluid secretion and the turnover of cAMP.

Peripheral inactivation of neurotensin. Isolation and characterization of a metallopeptidase from rat ileum

A peptidase that inactivated neurotensin by cleaving the peptide at the Pro10-Tyr11 bond, generating the biologically inactive fragments neurotensin(1-10) and neurotensin(11-13) was purified from whole rat ileum homogenate. The purified enzyme behaved as a 70-75-kDa monomer as determined by SDS-PAGE analysis in reducing or non-reducing conditions and gel permeation on Ultrogel AcA34. The peptidase was insensitive to thiol-blocking agents and acidic and serine protease inhibitors but could be strongly inhibited by 1,10-phenanthroline, EDTA, dithiothreitol and heavy metal ions such as zinc, copper and cobalt. Zinc was the only divalent cation able potently to reactivate the apoenzyme. This enzyme could be distinguished from endopeptidases EC 3.4.24.15 and EC 3.4.24.11, angiotensin-converting enzyme, proline endopeptidase, aminopeptidase and pyroglutamyl-peptide hydrolase since it was not affected by micromolar concentrations of their specific inhibitors. The peptidase displayed a high affinity for neurotensin (1.6 microM). Studies concerning the specificity of the enzyme towards the sequence of neurotensin established the following. (a) Neurotensin(9-13) was the shortest partial sequence that fully inhibited tritiated neurotensin degradation; shortening the C-terminal part of the neurotensin molecule led to inactive fragments. (b) Amidation of the C-terminal end of the peptide did not prevent the recognition by the peptidase. (c) There existed a strong stereospecificity of the peptidase for the residues in positions 8, 9 and 11 of the neurotensin molecule. (d) Pro-Xaa dipeptides (where Xaa represented aromatic or hydrophobic residues) were the most potent inhibitors of tritiated neurotensin degradation while all the Xaa-Pro dipeptides tested were totally ineffective. (e) The neurotensin-related peptides: neuromedin N, xenopsin and [Lys8-Asn9]neurotensin(8-13), as well as angiotensins I and II and dynorphins(1-8) and (1-13) were as potent as neurotensin in inhibiting [3H]neurotensin hydrolysis.

Elevated PGI2 and PGE2 production in the rat ileum following mild hypotension

Ileal prostaglandin (PGs) biosynthesis was compared in female rats in normal mild hemorrhage (exposed to mild hypotension, reperfusion, and maintenance on hyperalimentation for 5 days) and control groups (instrumentation and hyperalimentation without hemorrhage). Tissue PG levels were analyzed by radiochromatographic analysis of microsomal membrane fractions prepared from the ileum in each group. Total cyclooxygenase activity in the normal and control groups was modest, with low levels of 6-keto-PGF1 alpha, PGE2, PGF2 alpha, thromboxane B2, PGA2, and PGD2 being produced. Hemorrhage, reperfusion, and maintenance on hyperalimentation for 5 days markedly induced total cyclooxygenase activity in the female rat ileum. Ileal microsomal membrane fractions obtained from the mild hemorrhage group synthesized levels of individual PGs three- to seven-fold higher than the normal or control groups, with 6-keto- PGF1 alpha (breakdown product of prostacyclin), PGE2, and PGA2 demonstrating the highest levels of biosynthesis. These data suggest that the gastrointestinal tract could serve as a source for the elevated PGs known to occur in various shock models.

Single-villus analysis of disaccharidase expression by different regions of the mouse intestine

1. The present results describe how a new technique of whole-tissue cytochemistry can be combined with automatic scanning of microdissected villi to measure the capacity of individual villi to hydrolyse disaccharides in different parts of the small intestine. 2. Intact villi from the mouse proximal jejunum are found to be eight times more effective than ileal villi in hydrolysing 2-naphthyl-alpha-D-glucoside, an artificial substrate for enzymes normally hydrolysing sucrose, maltose, isomaltose and trehalose in adult intestine. Homogenates of jejunal scrapings are four times more effective than ileal homogenates in hydrolysing this substrate. This discrepancy arises from relating enzyme activities to homogenate protein in cases where intestinal structure changes. 3. The eightfold difference in villus alpha-glucosidase activity is associated with a threefold difference in villus surface area. This discrepancy in turn reflects changes in the capacity of individual enterocytes to express alpha-glucosidase during migration along the crypt-villus axis. These results emphasize the futility of trying to gauge intestinal function from measurement of intestinal structure. 4. Differences between ileal and jejunal villus alpha-glucosidase activities have been further partitioned into those depending on villus structure and those depending on enterocyte development. Present results are discussed in relation to the ability of luminal nutrition to maintain a proximal-distal gradient of digestive enzyme function in the small intestine. The general applicability of this method of analysis to other studies of adaptive response is also emphasized.

Effects of a high-protein, low-carbohydrate diet on degradation of sucrase-isomaltase in rat jejunoileum

During the degradation of intestinal sucrase-isomaltase by pancreatic proteinases, degradation of sucrase-active site precedes that of the isomaltase-active site in rats. In the present paper, we demonstrate that the extent of degradation of sucrase-isomaltase is altered by dietary manipulation in vivo. Adult rats were starved for 24 h and received either a standard diet (20 cal% protein, 55% carbohydrate) or an isocaloric high-protein, low-carbohydrate diet (70 cal% protein, 5% carbohydrate). Animals were killed 15 h after the refeeding. In rats fed a high-protein, low-carbohydrate diet, luminal trypsin activity was three times higher than controls, and sucrase activity in proximal ileum was significantly lower (P less than 0.001) than controls, whereas isomaltase activity was similar in both groups. In proximal jejunum, luminal trypsin activity was remarkably lower (P less than 0.01) than in proximal ileum in both groups; sucrase and isomaltase activity was similar in both groups. Crossed immunoelectrophoresis demonstrated that a degradation product of sucrase-isomaltase, i.e., isomaltase monomer, was present in a larger amount in rats fed a high-protein, low-carbohydrate diet. In rats with bypassed pancreatic ducts, the amount of this degradation product was decreased and effect of a high-protein, low-carbohydrate diet was abolished. Experiments with a sequential isolation of epithelial cells of proximal ileum revealed that sucrase activity was decreased along the entire height of the villus in animals fed a high-protein, low-carbohydrate diet.(ABSTRACT TRUNCATED AT 250 WORDS)

New, improved lanthanide-based methods for the ultrastructural localization of acid and alkaline phosphatase activity

New, improved techniques for the ultrastructural localization of acid and alkaline phosphatase activity using lanthanide cations as the trapping agent were developed. Delayed penetration of the capture ions and the incubation constituents into cellular compartments was prevented by pretreating specimens with borohydride/saponin. Both the concentration of the capture agent in the incubation medium and the incubation time of the tissue specimens were optimized to achieve a satisfactory cytochemical reaction and to avoid precipitation artefacts caused by local matrix effects. The conversion of cerium phosphate into the almost insoluble cerium fluoride minimized losses of the reaction product during postincubation processing. Moreover, lanthanum itself as well as lanthanides other than cerium, e.g., gadolinium and didymium (praseodymium, neodymium), were successfully applied and can be recommended as capture agents for phosphatase cytochemistry.

Maturational patterns of carbohydrases in the ileal remnant of rats after jejunectomy at infancy

The enteric epithelium of suckling rat undergoes dramatic functional and cytokinetic changes (redifferentiation) with maturation. Ileal epithelial maturation was studied in infant rats subjected to 60% proximal enterectomy at age 10 d in an effort to examine redifferentiation mechanisms. Two months after resection the residual ileal remnant was increased in diameter, weight, total protein, and DNA per unit length compared with ileal segments from control littermates that had laparotomy without resection. The residual ileum demonstrated increased sucrase activity per unit length but was indistinguishable from control ileal segments in activity per unit DNA or villus distribution. Lactase activity was negligible in all segments of the residual intestine. Villus height and crypt depth were increased in the residual ileum with slight increases in cell turnover and cell-migration rates. These results show the presence of an intrinsic program for regulation of ileal epithelial maturation and its resistance to alteration by a major stimulus applied before its expression.

Selective modulation of hepatic and ileal Na+-K+-ATPase by bile salts in the rat

Sodium-potassium adenosinetriphosphatase (Na+-K+-ATPase) is modulated by functional demands. We determine whether Na+-K+-ATPase specific activity was changed by oral administration of different bile salts and whether upregulation in the liver is due to increased numbers of catalytic units. In rats after bile duct drainage for 18 h, Na+-K+-ATPase activity was reduced to 50% of control in liver and ileum but unchanged in jejunum and kidney. Increased Na+-K+-ATPase activity after short-term feeding of bile salts was noted only following trihydroxy bile salts, i.e., taurocholate (100 mg/100 g body wt) increased hepatic Na+-K+-ATPase 143% and ileum 138% above control, whereas jejunum and kidney were unchanged. Chronic feeding of trihydroxy bile salts for 4 days increased hepatic Na+-K+-ATPase (214-260%) and alkaline phosphatase (189-274%), whereas 5'-nucleotidase and Mg2+-ATPase activities were unchanged from control. Plasma membrane Na+-K+-ATPase activity significantly increased as early as 4 h after taurocholate administration, whereas homogenate activity did not rise until 16 h; both reached a new steady state between 24 and 48 h. Sixteen hours after bile salt feeding, increased Na+-K+-ATPase activity was blocked by cycloheximide, and in the liver increased enzyme activity (179%) was associated with a comparable change in sodium-dependent [gamma-32P]ATP binding (162%) to liver plasma membrane fractions. These studies show Na+-K+-ATPase activity adapts selectively in liver and ileum following administration of trihydroxy bile salts, and the process involves increased density of Na+-K+ pump sites on the liver plasma membrane.

Similarity of the sugar moiety of human alkaline phosphatases between the kidney cortex and duodenum, or medulla and ileum

Characteristics of human renal cortex and medulla alkaline phosphatase (ALP) were compared. Enzymatic and hydrophobic properties of both ALPs were almost similar. However, the results of concanavalin A affinity chromatography and wheat germ agglutinin affinity electrophoresis, exhibited that sugar chain structure(s) might be different between the cortex and medulla ALPs. In addition, the molecular mass and substrate specificity differed from each other, and these results of cortex and medulla ALPs were well accordant with those of human duodenal and ileal ALPs, respectively, as described previously (Clin Chim Acta 1987;163:279-287).

Immunolocalization of blood group A gene specified alpha 1,3N-acetylgalactosaminyltransferase and blood group A substance in the trans-tubular network of the Golgi apparatus and mucus of intestinal goblet cells

The subcellular distribution of blood group A gene specified alpha 1,3N-acetylgalactosaminyltransferase and its product was studied in human intestinal goblet cells by immunoelectron microscopy. The O-glycosylation step yielding blood group A-active glycoconjugates occurred in the trans region of the Golgi apparatus as indicated by the presence of immunolabel for both antigens. In the Golgi apparatus, immunoreactive alpha 1,3N-acetylgalactosaminyltransferase was detectable in trans cisternae and in the trans-tubular network which was found to be continuous with the cisternal stack and exhibited acid phosphatase activity. This demonstrates that in intestinal goblet cells (i) the trans-tubular network does not constitute a compartment distinct from trans cisternae, and (ii) structures corresponding to GERL are structurally and functionally part of the Golgi apparatus. In addition to immunolabel for transferase at the inner surface of the cisternal membranes, luminally located immunolabel indicating the presence of free, not membrane-associated transferase became first detectable in the trans-tubular network and early forming mucus droplets contained therein. Further, the content of mature mucus droplets as well as the extracellular mucus layer were labeled. Absence of immunolabel in blood group 0 subjects lacking the blood group A gene specified transferase and the apparent non-reactivity of the antibodies with carbohydrate epitopes indicates that free alpha 1,3N-acetylgalactosaminyltransferase is present in mucus droplets and becomes secreted by intestinal goblet cells.

On the presence of intermediate cells in the small intestine

In the small intestine, the presence of transitional cells or cells intermediate between Paneth cells and goblet cells has been reported frequently for 100 years. Light microscopy and, more recently, fine structural studies have indicated that secretory granules observed in intermediate cells share some morphologic characteristics with those of granular goblet cells and of Paneth cells. In order to verify if intermediate cells in the jejunum and ileum of the adult mouse have functional similarities with either granular goblet or Paneth cells, we have studied the incorporation of sulfur-35 by radioautography and the localization of lysozyme by immunocytochemistry. After radioautography, goblet cells and, to a lesser extent, granular goblet cells had incorporated sulfur-35, whereas Paneth cells and intermediate cells were completely negative. Immunolocalization of lysozyme was done by using rabbit anti-rat lysozyme and protein A-peroxidase. After demonstration of peroxidase activity, only Paneth cells were stained and intermediate cells were negative. Therefore, intermediate cells do not contain sulfomucin or lysozyme, and they are functionally different from goblet and Paneth cells. Their function remains unknown.

A novel N-acetylglucosaminidase from neonatal rat enterocytes

The luminal surface of ileal enterocytes in fetal and neonatal mammals is covered by beta-hexosaminidase, which is attached to a fibrillar array. In this study, we have isolated this enzyme and subjected it to kinetic and structural analyses. The enzyme is identified as N-acetyl-beta-glucosaminidase (NA beta G) on the basis of substrate specificity and susceptibility to inhibition by N-acetylgalactosamine. Its catalytic properties and thermal stability are characteristics of the acidic, thermally labile human isoenzyme, but it differs from the human glycosidase in size. The neonatal NA beta G is a species of 225,000 relative mass (Mr), composed of two subunits of 125,000 and 115,000 Mr. Both its cellular location and differences in biophysical properties from the adult rat lysosomal forms and human glycosidases suggest that the neonatal rat NA beta G is a novel isoenzyme.

Effect of dietary carbohydrates on bacterial cholyltaurine hydrolase in poultry intestinal homogenates

The bile salt hydrolase activity in intestinal homogenates reflects composite activities of the gastrointestinal microbial consortia. We have proposed that specific transformations of conjugated bile acids by the intestinal microflora result in the production of metabolites which depress the growth of poultry. The influence of dietary carbohydrates on the physical and kinetic properties of cholyltaurine hydrolase activity, one such bile acid-transforming enzyme in gastrointestinal homogenates of young chickens, was characterized by using a sensitive radiochemical assay. Cholyltaurine hydrolase activity in crude extracts of ileal homogenates was increased twofold by 0.25% Triton X-100 and a freeze-thaw cycle. The pH optimum for cholyltaurine hydrolase from ileal homogenates was very broad and reflected the pH range of poultry intestinal contents (i.e., 5.8 to 6.4). The carbohydrate component of the diet did not affect the apparent temperature optimum (41 degrees C) or stability profile, nor did it affect the apparent Km for taurocholic acid hydrolysis (approximately 0.43 mM). The enzymes in intestinal homogenates were active on all taurine-conjugated bile acids tested. The carbohydrate component of the diet did, however, affect the specific activity of cholyltaurine hydrolase in ileal homogenates from chickens. The levels of cholyltaurine hydrolase activity (rye greater than sucrose greater than corn) in homogenates from birds fed the different diets were directly related to the amount of growth depression (rye greater than sucrose greater than corn) associated with feeding these dietary carbohydrates. These data suggest that intestinal levels of cholyltaurine hydrolase are correlated with the amount of carbohydrate-induced growth depression in poultry.

Fatty acid desaturation in the intestinal mucosa

Information as to the ability of the enterocyte to desaturate fatty acids is lacking. This is important in understanding whether the source of intestinal arachidonic (20:4(n-6) acid is biliary or from de novo synthesis. Delta 9- and delta 6-desaturase enzymes were assayed in homogenates of rat jejunum, ileum and liver. Rat small intestine possesses desaturase activity to convert palmitic (16:0) to palmitoleic (16:1) and linoleic (18:2(n-6) to linolenic (18:3(n-6) acid. Enzyme activities were highest in liver relative to activity in jejunal and ileal homogenates. It is concluded that delta 9- and delta 6-desaturase activities may have an important role in determining physico-chemical properties and thus transport properties of enterocyte membranes.

Contribution of the microflora to proteolysis in the human large intestine

Protease activities in human ileal effluent were approximately 20-fold greater than in normal faeces. Comparative studies with faeces from a person who did not have a pancreas suggested that a substantial proportion of the proteolytic activity in normal faeces was of bacterial origin. Thimerosal, iodoacetate, EDTA and cysteine significantly inhibited proteolysis in faeces, but not in small intestinal contents, showing that cysteine and metalloproteases were produced by bacteria in the large gut. These results, together with results from studies using p-nitroanilide substrates, demonstrated that faecal proteolysis was both qualitatively and quantitatively different from that in the small intestine. Studies with pure cultures of proteolytic gut bacteria indicated that the cell-bound proteases of Bacteroides fragilis-type organisms were likely to contribute significantly towards proteolytic activity associated with the washed cell fraction and washed particulate fraction of faeces. Extracellular proteases were formed by Streptococcus faecalis ST6, Propionibacterium acnes P6, Clostridium perfringens C16, Cl. bifermentans C21 and Cl. sporogenes C25. Inhibition results suggested that these bacteria, and similar organisms, may be partly responsible for the extracellular proteolytic activity found in the cell-free supernatant fraction of faeces.

Neutrophil-induced decrease in wound margin strength after intestinal anastomosis--influence on collagen and mechanisms of granulocyte action

A marked decrease in strength occurs early after surgery in tissues adjacent to an incisional wound. In this study measurement of collagen and a histological examination were carried out in a rat intestinal anastomosis. The decrease in tissue strength of the bowel wall did not correlate to the amount of collagen or to changes in collagen solubility. At histology the collagen layer was seen unaffected. Our previous studies showed that the decrease in strength was eliminated if the number of circulating neutrophils was reduced by antineutrophil serum. In addition, the decrease was counteracted by a proteinase inhibitor, the soybean trypsin inhibitor (STI), and the oxygen-free-radical scavengers superoxide dismutase (SOD) and catalase. To further examine the mechanisms of the decrease, neutrophil accumulation in the anastomosis was examined by myeloperoxidase (MPO) assay, and at histology, after treatment of the animals with the proteinase inhibitor, the scavengers or saline solution. MPO activity increased by 110% 24 h after the operation in saline-treated animals, but the increase was not influenced by STI or SOD and catalase. At the histological examination neutrophil accumulation was not seen affected by the drugs. Thus, the proteinase inhibitor and the scavengers counteract the decrease in strength in some other way than by reducing the number of neutrophils in the wound edges, for instance by local inhibition of neutrophil proteolytic enzymes and oxygen-free radicals.

Increased phospholipase A2 activity of Ileal mucosa in Crohn's disease

The activity of phospholipase A2 (EC 3.1.1.4) in endoscopic biopsy specimens of intestinal mucosa was compared in patients with Crohn's disease and controls without inflammatory bowel disease. In postresection Crohn patients there was significantly enhanced phospholipase A2 activity proximal to the anastomosis in the neoterminal ileum, whether or not the mucosa was inflamed at the time of biopsy. Highly elevated ileal phospholipase A2 activity had a predictive value for symptomatic relapse within 1 year after resection. Patients with concomitant Crohn's colitis, in whom the risk of ileal recurrence is particularly high, had greater ileal phospholipase A2 activity than noncolitis Crohn patients. Association thus was demonstrated between activity of phospholipase A2 in ileal mucosa and proneness to ileal inflammation in Crohn's disease.

Neurotensin metabolism in various tissues of central and peripheral origins: ubiquitous involvement of a novel neurotensin degrading metalloendopeptidase

The metabolism of neurotensin in vitro, in various membrane preparations and cell lines of central and peripheral origins was studied. Neurotensin degradation products were separated by HPLC and identified by either amino acid analysis or by their retention times. Peptidases responsible for the cleavages were identified by means of specific fluorigenic substrates or inhibitors. Although the patterns of neurotensin inactivation varied according to the tissue source in all cases, a major primary cleavage occurred at the Pro10-Tyr11 bond, leading to the biologically inactive fragments NT1-10 and NT11-13. A novel neurotensin-degrading metallopeptidase was responsible for this cleavage. Interestingly, it was the only peptidase that was ubiquitously detected. In addition, endopeptidase 24.11 (EC 3.4.24.11) contributed to this cleavage in rat brain synaptic membranes as well as in circular and longitudinal smooth muscle plasma membranes from dog ileum.

The nonspecific nature of the vanadate inhibition of rat ileal (NA,K)-ATPase

Vanadate has been suggested as an intracellular regulator of (Na+ + K+)-ATPase. To test this hypothesis we examined the stimulatory and inhibitory effects of vanadate on 86--Rb efflux and influx (measurements of the activity of the Na-pump) in rat ileum under conditions of normal, reduced and increased (Na+ + K+)-ATPase activity. The half maximal stimulation of the Rb efflux and the half maximal inhibition of the Rb influx were not different in the three conditions tested. This suggests that vanadate does not have a regulatory effect on the activity of the Na-K-transport enzyme. The vanadate effect seem rather, to be nonspecific in terms of being unrelated, on a mole per mole basis, to the activity of the (Na+ + K+)-ATPase enzyme.

Homodimer and heterodimer forms of adult rat intestinal alkaline phosphatase

Three forms of alkaline phosphatase have been isolated from different sections of the small intestine: F3 180 kDa from the duodenum; F2 150 kDa principally jejunal; F1 120 kDa the only ileal form. Their catalytic properties have been compared as well as the electrophoretic properties the dimer and monomer of their phosphorylated intermediates. Pi was a competitive inhibitor of F1 and F3, whereas glycerophosphate was competitive inhibitor only of F3. Pi was a non competitive inhibitor of F2 and of a mixture F1 plus F3. Heating the phosphorylated enzyme preparations led to their dissociation into the phosphorylated monomers: F1 and F3 appear to be homodimers 65 kDa and 90 kDa peptides respectively whilst F2 seems to be a dimer formed from one of each monomer. F1 was phosphorylated faster but less intensively than F3. F2 was strongly phosphorylated over a long time-course and its 65 kDa monomer fraction was phosphorylated more strongly for longer than that from F1.

Effect of inhibitors of enkephalin degradation in the isolated guinea-pig ileum

Bestatin and high concentration of puromycin increase the depressing effect of [Met] enkephalin on the twitch response of the electrically stimulated guinea-pig ileum. Thiorphan (enkephalinase A inhibitor) is hardly effective, but phelorphan (mercapto-acetyl-Phe-Phe) a newly synthesized enzyme-inhibitor which effectively inhibits the enkephalinase A, enkephalinase B and soluble aminopeptidase activity, potentiates the effect of enkephalin dose-dependently and in low concentrations (0.01-1 microM). Enkephalinase A, though present in these tissues, is not functional under the conditions of the test, because it is inhibited by the physiological buffer itself. These results demonstrate that enkephalinase B and the membrane bound aminopeptidase, but not the soluble aminopeptidase or enkephalinase A hydrolyse enkephalins in the isolated guinea-pig ileum.

[M-cholinergic regulation of Na+,K+-ATPase activity of vesicular preparations of sarcolemma from the myocardium and intestinal smooth muscles]

Acetylcholine (10(-7)-10(-2) M) enhanced the Na+, K+-ATPase activity in sarcolemmal vesicles from myocardium and intestinal smooth muscle. The stimulation of the enzyme from canine ventricles reaches 150% and was less pronounced (10-20%) in the case of frog myocardium and canine ileal muscles. The activating action of the neurotransmitter was simulated by gramicidin D (1-5 microM), but not by valinomycin 1-5 microM), blocked both by ouabain (200 microM) and atropine (0.1 microM), a muscarinic cholinergic antagonist. The activating action disappeared after treatment of membranes with alamethicin, a pore-producing antibiotic (0.8 mg/mg of protein). It is suggested that an increase in the Na+, K+-ATPase activity caused by acetylcholine is induced by Na+ which permeate the sarcolemmal vesicles through the ionic channel coupled with muscarinic acetylcholine receptor.

Short-term effect of a high-protein/low-carbohydrate diet on aminopeptidase in adult rat jejunoileum. Site of aminopeptidase response

The short-term effects of high-protein/low-carbohydrate diet on aminopeptidase N activity were studied in the brush-border membranes of proximal jejunum and proximal ileum of adult rats. The animals were starved overnight and re-fed for 15 h either with a standard diet (20% protein, 55% carbohydrate, in terms of energy content) or with a high-protein/low-carbohydrate diet of equal energy content (70% protein, 5% carbohydrate). All rats consumed similar amounts of diet, and measurements were made 15 h after initiation of re-feeding. In the proximal jejunum a slight increase in aminopeptidase activity was observed after the high-protein intake. In contrast, considerable stimulation (52%) of the enzyme specific activity was obtained in the proximal ileum. This increase in ileal aminopeptidase activity was more prominent in the mature cells of the upper villus. To determine if the increase of aminopeptidase activity was due to an increased amount of enzyme protein, rocket immunoelectrophoresis was performed with detergent-solubilized brush-border protein from ileum on agarose gels containing anti-(rat brush-border) antiserum. When the same amount of enzyme activity was loaded on the gels, the peaks of immunoprecipitate for aminopeptidase were similar for animals fed on a standard or a high-protein diet. When the same amount of protein was loaded, the peak of immunoprecipitate for aminopeptidase was higher (81%) after a high-protein diet. These results showed that the high protein intake evoked an increase in aminopeptidase activity, with a concomitant increase in the amount of immunoreactive protein.