bluuebunny/crossref_metadata_2025 huggingface dataset:
Intraluminal and intracellular phases of fat absorption are impaired in essential fatty acid deficiency
Authors: Levy E. , Garofalo C. , Thibault L. , Dionne S. , Daoust L. , Lepage G. , Roy C. C.
Published: December 2017

The structure and function of enterocyte membranes are particularly sensitive to the degree of fatty acid saturation. The objective of the present study was to assess intestinal fat transport in essential fatty acid (EFA)-deficient animal models. Both the digestive and absorptive phases leading to the formation and the secretion of triglyceride (TG)-rich lipoproteins were investigated. After an intraduodenal fat infusion, the percentage increase of plasma TG over fasting values was examined over a period of 4 h in two groups of control and EFA-deficient rats. Lower values at 1 and 2 h (P less than 0.05) were observed in EFA-deficient rats, suggesting fat malabsorption. Likewise, postprandial chylomicronemia was diminished. In a separate group of rats, EFA deficiency was associated with reduced TG and chylomicron-TG transport into lymph. Although pancreatic lipase activity did not change (47.1 vs. 46.2 mumol free fatty acids.mg protein-1.h-1), bile flow was decreased over the 8-h period of collection. Concomitantly, a significant decline (nmol.min-1.g liver-1, P less than 0.05) was discernible in the biliary secretory rate of bile salts (14.09 +/- 2.13 vs. 35.09 +/- 3.73), phospholipids (7.01 +/- 0.61 vs. 11.79 +/- 1.65) and cholesterol (0.19 +/- 0.01 vs. 0.83 +/- 0.06). In vitro studies, utilizing everted sacs incubated with mixed micelles, revealed that EFA-deficient jejunal segments of rats incorporated and esterified less [14C]oleic acid (21 and 32%, respectively). Moreover, the synthesis and secretion of TG-rich lipoproteins were found markedly reduced in mouse jejunal explant cultures. We conclude that EFA deficiency modifies both the intraluminal and intracellular phases of fat absorption.
A complex avian intestinal motility response to fasting
Authors: Clench M. H. , Mathias J. R.
Published: December 2017

The rhythmic oscillating complex (ROC) is described from a series of experiments that surveyed the myoelectric activity of the avian small intestine as recorded from chronically implanted bipolar electrodes. A highly organized myoelectric event in the fasting avian small intestine, the ROC is demonstrated in detail in chickens (Gallus); it is also found in other gallinaceous birds but not in owls (Strix) or mammals. The ROC comprises rapidly propagating bursts of spike potentials (SPBs) that occur in a regular and predictable pattern: single orad SPBs alternate with groups of aborad SPBs. An average ROC in a chicken contains a mean of 78.9 +/- 2.0 (mean +/- SE) SPBs (37% orad, 63% aborad) that rapidly traverse the full length of the small intestine. The aborad SPBs move at mean velocities of 25.0 +/- 0.5 cm/s and last a mean of 0.9 +/- 0.0 s at an electrode site; the orad SPBs are faster (41.2 +/- 2.3 cm/s) and longer in duration (1.3 +/- 0.0 s). ROC activity continues for a mean of 7.6 +/- 0.2 min. ROCs occur only in a well-fasted gut as often as every 3 h and apparently for as long as the bird remains without food. Because ROCs restimulate fed-state activity in the stomach and small intestine, we hypothesize that they recycle nutritive material for further digestive activity in the distal tract.
Peptone stimulates gastrin secretion from the stomach by activating bombesin/GRP and cholinergic neurons
Authors: Schubert M. L. , Coy D. H. , Makhlouf G. M.
Published: December 2017

The mechanism by which partly digested protein (peptone) stimulates gastrin secretion was examined in isolated antral tissues with intact intramural innervation. In the isolated vascularly perfused rat stomach, luminal perfusion with 0.5% peptone increased gastrin (62 +/- 14 pg/min; P less than 0.01) and decreased somatostatin (74 +/- 19; P less than 0.01) secretion. The axonal blocker tetrodotoxin (TTX) abolished the gastrin and somatostatin responses indicating that the responses were neurally mediated. Atropine partly inhibited the gastrin response (50%) and converted the somatostatin response to an increase above basal level. The selective bombesin/gastrin-releasing peptide (GRP) antagonist [Leu13-psi(CH2NH)-Leu14]-bombesin partly inhibited the gastrin response (65%) and caused a further decrease in somatostatin secretion. A combination of atropine and the bombesin/GRP antagonist, like TTX, abolished the gastrin and somatostatin responses. The pattern of response to peptone in superfused antral segments was identical to that in the vascularly perfused stomach. In fundic segments that do not secrete gastrin, the somatostatin response to peptone alone and with various antagonists was identical to that in antral segments. The results indicate that peptone stimulates gastrin secretion by activating stimulatory cholinergic and bombesin/GRP neurons. Cholinergic neurons stimulate gastrin directly as well as indirectly by eliminating the inhibitory paracrine influence of somatostatin.
Amylase release from streptolysin O permeabilized fetal pancreatic acini
Authors: Cher D. J. , Padfield P. J. , Jamieson J. D.
Published: December 2017

Developmental regulation of Ca(2+)-dependent protein discharge was investigated in fetal and neonatal rat pancreatic acini permeabilized with streptolysin O. When incubated at 37 degrees C in a Ca(2+)-ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid/K glutamate buffer, permeabilized day 19 and 20 fetal acini demonstrated Ca(2+)-dependent release of amylase, whereas day 21 (term) fetal acini did not. Ca(2+)-dependent amylase release reappeared in day 1, 2, and 6 neonatal pancreases. ATP depletion completely inhibited Ca(2+)-stimulated amylase release from both day 20 fetal and adult acini. Ca(2+)-dependent amylase discharge from day 20 fetal acini was enhanced by the nonhydrolyzable GTP analogue, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), and by the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA). Ca(2+)-independent GTP gamma S-stimulated amylase release was observed from adult but not from day 20 fetal acini. In contrast to its stimulatory effects in permeabilized adult acini, adenosine 3',5'-cyclic monophosphate (cAMP) alone had little effect on release from permeabilized day 20 fetal acini. Our studies indicate that the fetal pancreas is competent to undergo Ca(2+)-dependent protein secretion but that this secretion is suppressed at birth. Our studies also suggest that the fetal gland is sensitive to modulators of exocytosis active in the adult pancreas, such as GTP gamma S, TPA, and cAMP but responds differently to these agents compared with responses in adult glands.
Increased apolipoprotein A-IV in rat mesenteric lymph after lipid meal acts as a physiological signal for satiation
Authors: Fujimoto K. , Cardelli J. A. , Tso P.
Published: December 2017

Chylomicron transport and apolipoprotein A-IV (apo A-IV) output in mesenteric lymph increases significantly after a lipid meal. Mesenteric lymph collected from lymph-fistula rats after lipid infusion exerted an anorectic effect on 24 h fasted rats after administration through chronically indwelling right atrial catheter. Lymph before lipid infusion and lymph collected from a rat fed lipid plus Pluronic L-81 (a potent inhibitor of chylomicron formation) had no anorectic effect. Chylomicron and apo A-IV-rich lymph lost its anorectic effect after specific immunoprecipitation of apo A-IV by a monospecific antibody. Intravenous infusion of the same amount of purified apo A-IV as in chylous lymph 6-8 h after a lipid meal suppressed food intake. This unique physiological function of apo A-IV is not shared by apolipoprotein A-I. It is proposed that apo A-IV is a circulating signal released in response to fat feeding and that it is likely to mediate the anorectic effect of a lipid meal.
Stimulation of intramural secretory reflex by luminal distension pressure in rat distal colon
Authors: Itasaka S. , Shiratori K. , Takahashi T. , Ishikawa M. , Kaneko K. , Suzuki Y.
Published: December 2017

The effects of distension on epithelial transport were examined by increasing intraluminal pressure in the rat distal colon in vitro. Two kinds of preparation, one with the musculature intact (intact preparation) and the other with the musculature and the myenteric neurons detached (mucosa-submucosa preparation), were used and the transmural potential difference (PD) changes were measured. In the intact preparation, distension with a luminal pressure of 15 cmH2O for 15 s caused a transient increase in PD (the lumen being more negative) of 3.7 +/- 0.6 mV. The distension-induced increase in PD was largely sustained when the pressure was applied for 10 min. Distension caused by intraluminal pressure, if it is of a similar degree to that caused by fecal pellets, is enough to elicit a PD increase. The distension-induced PD increase was largely abolished by the removal of Cl- from the bathing solution, or by the addition of furosemide or bumetanide. In the mucosa-submucosa preparation, distension with a luminal pressure of 15 cmH2O for 15 s caused an increase in PD of 5.8 +/- 0.6 mV. The distension-induced increase in PD was partially inhibited by atropine and was further decreased in the presence of tetrodotoxin both in the intact and mucosa-submucosa preparation. Indomethacin reduced the distension-induced PD increase in both preparations. These results suggest that distension by increased intraluminal pressure elicits the activation of Cl- secretion, which is mediated by submucosal plexus neurons. In addition, this distension-induced reflex is likely to be activated by normal fecal pellets.
Effect of aspirin on ulcer site blood flow in cat stomachs
Authors: Lau A. T. , Graham G. G. , Day R. O. , Perry M. A.
Published: December 2017

Radioactive microspheres were used to measure blood flow in the cat stomach during exposure to saline, 0.075 M HCl, and then 15 and 30 min after exposure to 20 or 40 mM aspirin in HCl. At the end of the experiment, the stomach wall was divided into ulcerated regions and adjacent nonulcerated areas. When exposed to saline, both regions had similar blood flow: 27 +/- 5 and 25 +/- 5 ml.min-1.100 g-1 (means +/- SE). Addition of acid caused a significant increase in blood flow to 41 +/- 7 ml.min-1.100 g-1 only at those sites that eventually ulcerated in the presence of aspirin. In the adjacent nonulcerated regions, blood flow was 31 +/- 5 ml.min-1.100 g-1 and was not significantly greater than the flow recorded during saline exposure. Aspirin caused ulcer site blood flow to increase dramatically to 89 +/- 12 and 122 +/- 18 ml.min-1.100 g-1 after 15 and 30 min, whereas the adjacent nonulcerated tissue rose to 40 +/- 6 and 44 +/- 5 ml.min-1.100 g-1, respectively. The ulcer site hyperemia with acid alone suggests higher mucosal permeability in these regions allowing back-diffusion of acid and injurious agents. The present data obtained in the cat do not support the notion that ischemia plays a role in initiating nonsteroidal anti-inflammatory drug (NSAID)-induced ulcers, but rather that acute NSAID ulcers are associated initially with a hyperemia.
Subacinar distribution of hepatocyte membrane potential response to stimulation of gluconeogenesis
Authors: Lee S. M. , Clemens M. G.
Published: December 2017

Isolated rat livers were perfused and the membrane potentials of matched periportal and pericentral hepatocytes were determined using glass microelectrodes. O2 uptake and gluconeogenesis were increased by both phenylephrine and glucagon and the extent of the increase was not affected by the direction of perfusion. With no exogenous substrate, hepatocyte membrane potentials were approximately -27 mV. No gradients were found. Substrate produced hyperpolarization in all hepatocytes, with a small but significant gradient produced. Phenylephrine-induced hyperpolarization was higher in periportal than in pericentral hepatocytes during anterograde perfusion, but reversed during retrograde perfusion. Similar effects on membrane potential were produced by phorbol myristate acetate (PMA). Glucagon hyperpolarized homogeneously during both anterograde and retrograde perfusion with no gradients across the acinus. Octanol addition during glucagon stimulation, however, resulted in heterogeneity similar to phenylephrine or PMA. Thus when hepatocytes are stimulated by substrate or hormones, the degree of hepatocyte membrane potential heterogeneity across the acinus is highly dependent on the nature of the stimulus. We propose that the differential hormone effects on hepatocyte membrane potential may be mediated at least in part by differential modulation of cell to cell communication via gap junctions.
Effects of agonists on p21ras and ras-related proteins in rat pancreatic acinar cells
Authors: Zimmermann P. , Schnefel S. , Zeuzem S. , Profrock A. , Haase W. , Schulz I.
Published: December 2017

This study shows the presence of seven different low-molecular-weight GTP binding proteins (smg proteins) with molecular masses between 18 and 27 kDa in subfractions of rat pancreatic acinar cells. After stimulation of isolated intact and permeabilized pancreatic acinar cells with cholecystokinin octapeptide (CCK-OP), the diacylglycerol (DG) analogue 12-O-tetradecanoylphorbol 13-acetate (TPA), vasoactive intestinal peptide (VIP), adenosine 3',5'-cyclic monophosphate (cAMP), or guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), [alpha-32P]GTP binding to 21- to 22-kDa smg protein(s) in microsomal membranes (MM) was reduced, whereas the [alpha-32P]GTP binding to 23-kDa protein(s) was enhanced. In addition, prestimulation of permeabilized cells with GTP gamma S caused enhancement of [alpha-32P]GTP binding to a 19-kDa protein in MM [immunologically identified as the ADP-ribosylation factor (arf)]. In the presence of cytosol, direct addition of GTP gamma S to isolated MM resulted in an apparent translocation of the 19-kDa protein (arf) from the cytosol to membranes. This indicates increased association of arf with the membrane in its GTP-bound state. In CCK-OP-prestimulated acinar cells, [alpha-32P]GTP binding to plasma membrane-located 21- to 22-kDa proteins (immunologically identified as p21ras proteins) was enhanced, suggesting that there is an interrelationship between p21ras proteins and CCK receptors. Our results give evidence for a role of 19-kDa, 21- to 22-kDa, and 23-kDa smg proteins in cAMP-protein kinase A- and DG-protein kinase C-mediated stimulation of intracellular pathways in pancreatic acinar cells.
Effects of fractionated doses of ionizing radiation on colonic motor activity
Authors: Otterson M. F. , Sarna S. K. , Leming S. C. , Moulder J. E. , Fink J. G.
Published: December 2017

The colonic motor effects of fractionated irradiation were studied in five conscious dogs. Seven colonic and two ileal strain gauge transducers were implanted. After control recordings, an abdominal dose of 250 cGy was administered three times a week on alternate days for three successive weeks (total dose 2,250 cGy). Recordings were then continued for 3 wk after the completion of radiation. Colonic giant migrating contractions (GMCs) occurred at a frequency of 0.15 +/- 0.05 contractions/h in the control state. Only one of these contractions (8.3%) originated in the small bowel and propagated into the colon. Abdominal field irradiation significantly increased the incidence of colonic GMCs to 0.51 +/- 0.11 contractions/h (P < 0.05). Fifty-four percent of GMCs originated in the small intestine. GMCs during the radiation schedule were associated with explosive diarrhea on seven occasions. Irradiation did not alter the frequency of colonic migrating motor complexes, but the mean duration of contractile states decreased in the middle and distal colon. Diarrhea occurred as early as the second dose of radiation. Pathological changes in the colon were correlated with motor activity. Both small intestinal and colonic GMCs reverted to control frequencies after cessation of radiation exposure. Abdominal irradiation significantly altered the contractile activity of the colon. These changes are associated with abdominal cramping and diarrhea.
Constitutive expression of the taurine transporter in a human colon carcinoma cell line
Authors: Tiruppathi C. , Brandsch M. , Miyamoto Y. , Ganapathy V. , Leibach F. H.
Published: December 2017

The human colon carcinoma cell line HT-29, when grown to confluence, was found to take up taurine and accumulate it against a concentration gradient from a NaCl-containing uptake medium. Replacement of NaCl with choline chloride almost totally abolished the uptake. Taurine uptake was dependent not only on Na+ but also on Cl-, because other anions failed to support the uptake in the presence of Na+. The uptake process was specific for beta-amino acids such as taurine, hypotaurine, and beta-alanine. Apparently, a single transport system with a Michaelis-Menten constant of 10.6 +/- 0.3 microM was responsible for the uptake. Stoichiometric analyses revealed that the Na+:taurine coupling ratio was 2:1, whereas the Cl-:taurine coupling ratio was 1:1. Culture of the cells in the presence of taurine caused downregulation of the uptake system. These cells were also capable of accumulating beta-alanine against a concentration gradient in the presence of NaCl. Beta-Alanine uptake occurred via a single transport system with an apparent Michaelis-Menten constant of 36 +/- 2 microM. Taurine and beta-alanine exhibited mutual interaction during uptake. Kinetic experiments strongly suggested that a common transporter was responsible for the uptake of these two beta-amino acids. It is concluded that the HT-29 cells constitutively express the taurine transporter and that this cell line may be a suitable model for investigations of intestinal taurine transporter.
Histamine potentiation by hydroxylamines: structure-activity relations; inhibition of diamine oxidase
Authors: Rangachari P. K. , Prior T. , Bell R. A. , Huynh T.
Published: December 2017

Hydroxylamines potentiated the responses of the canine colonic epithelium to histamine but not to other agonists such as serotonin or carbachol. We tested the hypothesis that an inhibition of histamine catabolism could explain the observed potentiation. A clear structure activity relation was defined, active compounds having the structure NH2-O-R, R being a simple uncharged aliphatic group. Active compounds delayed the disappearance of histamine from the bathing solutions and inhibited colonic diamine oxidase, an effect mimicked by standard inhibitors aminoguanidine and semicarbazide. Histamine agonists that possessed an imidazole nucleus (2- and 4-methylhistamine) were affected, whereas impromidine, 2 pyridylethylamine, and dimaprit were not. Agonist specificity combined with the enzyme data suggest an inhibition of histamine catabolism as a possible mechanism for the potentiating effects observed.
Organic cation transport by rat liver plasma membrane vesicles: studies with tetraethylammonium
Authors: Moseley R. H. , Jarose S. M. , Permoad P.
Published: December 2017

Recently, an organic cation:H+ antiport was selectively identified on the sinusoidal domain of rat liver with the use of the endogenous organic cation N1-methylnicotinamide (NMN). Absence of NMN+:H+ exchange on canalicular membrane suggested that this transport process was primarily involved in organic cation uptake, leaving the mechanism(s) for organic cation secretion into bile unknown. To further define hepatic organic cation transport, we examined the characteristics of tetraethylammonium (TEA) transport in basolateral (blLPM) and canalicular (cLPM) rat liver plasma membrane vesicles. In cLPM vesicles, under voltage-clamped conditions, an outwardly directed H+ gradient stimulated [14C]TEA uptake compared with [14C]TEA uptake under pH-equilibrated conditions, consistent with electroneutral TEA:H+ exchange. The proton ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone had no effect on [14C]TEA uptake, demonstrating that pH-dependent [14C]TEA uptake was not the result of a H+ diffusion potential. In the absence of a pH gradient, the intravesicular presence of TEA trans-stimulated uptake of [14C]TEA. Procainamide ethobromide (PAEB), vecuronium, and tributylmethylammonium (TBuMA), organic cations selectively excreted in bile, cis-inhibited pH-dependent TEA uptake. In contrast, in blLPM vesicles, no pH gradient-dependent [14C]TEA uptake was demonstrated. Instead, basolateral [14C]TEA uptake was significantly stimulated by a valinomycin-induced intravesicular-negative K+ diffusion potential. Basolateral [14C]TEA uptake was also cis-inhibited by PAEB, vecuronium, and TBuMA, but not by NMN. Conversely, PAEB, vecuronium, and TBuMA had no effect on basolateral pH-dependent [3H]NMN uptake. These findings suggest that organic cation transport, with TEA as a model quaternary amine, across the canalicular membrane is driven by an electroneutral organic cation:H+ exchange and that the transport of certain organic cations across the basolateral membrane is via a carrier-mediated system stimulated by an inside-negative membrane potential.
Somatostatin restraint of gastrin secretion in pigs revealed by monoclonal antibody immunoneutralization
Authors: Holst J. J. , Jorgensen P. N. , Rasmussen T. N. , Schmidt P.
Published: December 2017

We studied the functional coupling between antral somatostatin and gastrin cells in isolated perfused porcine antrum using immunoneutralization with monoclonal antibodies against somatostatin. Their binding affinity was 10(11) l/mol, and the final binding capacity was 11.7 nmol/ml. Antibody infusion within 1 min increased gastrin secretion, reaching a rate of 349 +/- 64% (means +/- SE, n = 7) of basal secretion (59 +/- 5 pmol/l) after 5 min. The effect of somatostatin at 10(-9) mol/l, which inhibited gastrin secretion from 58 +/- 11 to 14 +/- 3 pmol/min (n = 4), was abolished by antibody infusion. Electrical stimulation of the vagus nerves (n = 7) performed during antibody infusion increased gastrin secretion from 224 +/- 61 to 328 +/- 55 pmol/min, not significantly different from the increase in control experiments from 43 +/- 9 to 118 +/- 20 pmol/min, indicating that the vagal stimulation of gastrin secretion does not depend on mechanisms involving somatostatin. We conclude that paracrine antral somatostatin secretion is one of the most important factors regulating basal gastrin secretion in pigs.
Organic cation transport by rat hepatocyte basolateral membrane vesicles
Authors: McKinney T. D. , Hosford M. A.
Published: December 2017

Hepatocyte basolateral membrane possesses transport systems for mediated uptake of organic cations, the first step in the subsequent biliary excretion and/or metabolism of these compounds. The purpose of these studies was to evaluate potential mechanisms for transport of this class of solutes across this membrane by measuring 3H-labeled tetraethylammonium ([3H]TEA) transport into rat hepatocyte basolateral membrane vesicles. [3H]TEA uptake was stimulated by an outwardly directed proton gradient consistent with TEA-proton exchange. Proton gradient-stimulated [3H]TEA uptake was inhibited by quinidine and by the combination of valinomycin and carbonyl cyanide m-chlorophenylhydrazone (CCCP) but not by CCCP alone or by N1-methylnicotinamide (NMN). An outwardly directed TEA gradient also stimulated uptake of [3H]TEA with values at early time points exceeding those at equilibrium. This trans-stimulation or countertransport was saturable with an apparent Michaelis constant of 106 microM and maximal velocity of 434 pmol.mg-1.15 s-1. TEA countertransport was cis-inhibited by quinidine, cimetidine, and thiamine and by low temperature, but not by NMN. Thiamine was also capable of trans-stimulating [3H]TEA uptake. An outwardly directed potassium gradient enhanced and an inwardly directed potassium gradient reduced TEA countertransport but had no effect on [3H]TEA uptake occurring in the absence of other electrochemical driving forces. These studies indicate that there are at least two potential mechanisms in the hepatocyte basolateral membrane for transport of organic cations; organic cation-organic cation exchange (countertransport) and organic cation-proton exchange. Furthermore, the results are consistent with the existence of more than one transporter with different substrate affinities in each of these categories.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of intestinal epithelial proliferation: a few answers, many questions
Authors: Podolsky D. K.
Published: December 2017

The epithelium of the gastrointestinal tract mucosa is a highly dynamic and diverse mixture of cell populations requiring exquisite integration of the processes of cellular proliferation, differentiation, and senescence. It is likely that the proliferative compartment of the intestinal epithelium encompasses a hierarchy of totipotent and pluripotent stem cells in a manner similar to that which generates diversity in hematopoietic cell populations. Identification and characterization of the stem cell and progenitor populations in the intestine has been limited by the absence of markers or culture systems to identify these cells. Regulation of the proliferative compartment may be accomplished through the combined integration of key peptide growth factors and constituents of the extracellular matrix. The relative contribution of the epithelial populations themselves and the contributions made by associated cell populations such as pericryptal fibroblasts remain unclear. Recent studies have suggested that the transforming growth factors-alpha and -beta, two structurally unrelated peptide growth factors, might serve to regulate the balanced proliferation and turnover of intestinal epithelial cells. The proproliferative effects of TGF-alpha may be counterbalanced by the proliferation-inhibiting TGF-beta. Recent studies have demonstrated close interregulation of these peptides, which act through autocrine and paracrine mechanisms in model intestinal epithelial cell lines.
Electroneutral uptake and electrogenic secretion of a fluorescent bile salt by rat hepatocyte couplets
Authors: Weinman S. A. , Graf J. , Veith C. , Boyer J. L.
Published: December 2017

The role of membrane voltage as a driving force for the hepatic uptake and secretion of fluorescent bile salts has been examined in isolated hepatocyte couplets. The present study demonstrates that the fluorescent bile salt derivative (N-[7-(nitrobenz-2-oxa- 1,3-diazol-4-yl)]-7-amino-3 alpha, 12 alpha-dihydroxy-5-cholan-24-oyl)-2-aminoethanesulfonate (7 beta-NBD-NCT) is taken up into hepatocytes by a saturable process with a Kt of 2.7 microM. Uptake rate was reduced by only 22% after total Na+ replacement and was independent of transmembrane potential difference over a range of -135 to +25 mV. In contrast, secretion into the canalicular space was strongly dependent on membrane voltage over the range from -34 to 0 mV in a manner consistent with electrodiffusion of an anion. Fitting the secretion time course to that predicted by electrodiffusion demonstrated that only approximately 50% of total secretion can result from electrodiffusion. Studies in isolated perfused liver confirmed this observation that depolarization caused a decrease in bile salt secretion rate. These results demonstrate that 7 beta-NBD-NCT is transported by a neutral uptake process at the sinusoidal membrane and is secreted across the canalicular membrane in part by electrogenic transport. This suggests that voltage changes could be a common pathway resulting in impaired organic anion secretion in diverse cholestatic syndromes.
Effect of varying the rate and pattern of gastric distension on its sensory perception and motor activity
Authors: Khan M. I. , Read N. W. , Grundy D.
Published: December 2017

The aim of the present study was to see if varying the rate and pattern of gastric distension affected its motor and sensory responses to distension. A balloon was used to carry out distensions in male volunteers at constant rates of 20, 50, 100, and 200 ml/min. In addition rapid (75 ml/s) intermittent distensions (RID) were carried out with the use of a large hand-held syringe. Subjects were asked to indicate the first perception of the balloon, fullness, and discomfort. Increasing the rate of ramp distension caused all sensations to occur at higher volumes and higher pressures and reduced the frequency and amplitude of phasic oscillations in gastric pressure. During RID, the same sensations were experienced at much reduced volumes but were poorly sustained. These data suggest that ramp and RID are likely to induce gastric sensations by activating different populations of receptors. The responses to ramp distension are compatible with the activation of stretch receptors situated in parallel with the muscle elements, whereas RID appear to be activating a different population of rapidly adapting mechanoreceptors possibly situated in the mucosa.
Protection against hydrophobic bile salt-induced cell membrane damage by liposomes and hydrophilic bile salts
Authors: Sagawa H. , Tazuma S. , Kajiyama G.
Published: December 2017

Under physiological circumstances, cell membrane damage is not evident in biliary systems, despite the fact that hydrophobic bile salts are known to induce such damage by their detergent effects. The aim of this study was to determine the cytoprotective effects of liposomes and hydrophilic bile salts against hydrophobic bile salt-induced cell membrane damage, with the use of hemolysis of erythrocytes as a model of cytotoxicity. Washed human erythrocytes were incubated for 10, 30, 60, 90, and 120 min in buffered media (pH 7.45) containing increasing concentrations of different bile salts (1, 2.5, 5, 25, 50 mM). The cytotoxicity of the bile salts was found to be dose and time dependent and was correlated to the degree of the hydrophobicity of the bile salts as determined by the retention factor in reversed-phase high-performance liquid chromatography. Hydrophobic bile salt-induced hemolysis was reduced by liposomes and hydrophilic bile salts. Cytoprotection by liposomes was related to the degree of saturation of the fatty acyl chains, and cytoprotection by hydrophilic bile salts was related to their hydrophilicity. These in vitro findings indicate that vesicles may play a role in protection against cell membrane damage by hydrophobic bile salts in biliary systems and that such damage may be caused by an imbalance between hydrophobic and hydrophilic bile salts.
Multiple kinases phosphorylate the pancreatic cholecystokinin receptor in an agonist-dependent manner
Authors: Gates L. K. , Ulrich C. D. , Miller L. J.
Published: December 2017

The cholecystokinin (CCK) receptor on the rat pancreatic acinar cell is a guanine nucleotide-binding protein (G protein)-coupled receptor, which was recently demonstrated to be phosphorylated in response to agonist stimulation (Klueppelberg et al., J. Biol. Chem. 266: 17744-17746, 1991). In this work, we establish that this receptor is phosphorylated in response to a variety of homologous and heterologous secretagogues and that these phosphorylation events represent action by more than one protein kinase. One subgroup of kinases includes one or more isotype of protein kinase C (PKC), and is capable of playing a role in homologous and heterologous desensitization. A second subgroup of kinases that acts on the CCK receptor was defined by its resistance to 10 microM staurosporine, which was shown to inhibit all PKC in these cells. The activity of the second group of kinases was observed only in response to occupation of the CCK receptor by high concentrations of native hormone, raising the possibility of a "receptor-specific kinase." Similar to the prototypical kinase, beta-adrenergic receptor kinase (beta-ARK), this activity was inhibited in permeabilized cells by heparin. Furthermore, like this enzyme activity, beta-ARK was shown to be resistant to staurosporine. Based on its action on a G protein-coupled receptor, its activation at high concentrations of native agonist, and its pattern of inhibition, we believe that the staurosporine-insensitive CCK receptor kinase activity represents either beta-ARK or a closely related member of the receptor-specific kinase enzyme family.
Effects of valinomycin on osmotic lysis of zymogen granules and amylase exocytosis from parotid acini
Authors: Takuma T. , Ichida T. , Okumura K. , Sasaki Y. , Kanazawa M.
Published: December 2017

The role of osmotic swelling of the secretory granules in adenosine 3',5'-cyclic monophosphate (cAMP)-mediated amylase exocytosis was evaluated by use of isolated zymogen granules and saponin-permeabilized acini of the rat parotid gland. The osmotic lysis of the isolated granules was markedly enhanced by the addition of valinomycin (> 10(-9) M) in the presence of isosmotic KSCN or KI medium. However, valinomycin (up to 10(-5) M) did not increase the granule lysis in KCl medium, although the granules were slightly less stable in KCl medium than in K2SO4 or potassium gluconate medium. Guanosine 5'-O-(3-thiotriphosphate) did not affect the granule lysis. Valinomycin alone had no effect on amylase release from saponin-permeabilized parotid acini incubated in KCl medium, but completely abolished cAMP-mediated amylase release in all K+ media used. The inhibition was clearly detected at 0.1 microM valinomycin in KCl medium, not blocked by the addition of 1 mM MgATP to the medium, and was greatly reduced in NaCl medium. cAMP-evoked amylase release was completely inhibited by SCN- and I- (permeant anions), the mean inhibitory dosages of which were approximately 25 and 50 mM, respectively. These results suggest that 1) the membrane of parotid zymogen granules has no detectable Cl- channels responsible for osmotic swelling of the granules, and 2) increase in K+ or anion conductance of the granule does not enhance but inhibits cAMP-mediated amylase exocytosis from parotid acini.
Effect of 1,25(OH)2D3 and its analogues on membrane phosphoinositide turnover and [Ca2+]i in Caco-2 cells
Authors: Tien X. Y. , Brasitus T. A. , Qasawa B. M. , Norman A. W. , Sitrin M. D.
Published: December 2017

Our laboratory has recently reported that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] rapidly stimulates membrane polyphosphoinositide turnover and increases intracellular calcium concentration ([Ca2+]i) in Caco-2 cells. The role of binding to the vitamin D receptor (VDR) in the regulation of these rapid biochemical events, however, remains unclear. The present studies were, therefore, conducted using analogues of 1,25(OH)2D3, which differ markedly in their affinities for the VDR, to assess and compare their effects on [Ca2+]i and on inositol 1,4,5-trisphosphate (IP3) formation. Competitive binding studies performed with both intact cells and high-salt cytosolic extracts from Caco-2 cells demonstrated that 1,25(OH)2D3 and 1,24-(OH)2-22-ene-24-cyclopropyl-D3 (BT) have high affinities for the VDR; 25(OH)-16-ene,23-yne-D3 (AT), however, has a much lower affinity (approximately 1,000-fold less) for the VDR. Despite these large differences in binding affinities for the VDR, AT and BT produced similar concentration-dependent increases in [Ca2+]i and in IP3 formation while 1,25(OH)2D3 was approximately 10-fold less active. These results indicate that the structural requirements for the rapid action of these secosteroids on signal transduction in Caco-2 cells are different from those for receptor binding and transcriptional regulation.
Gastrointestinal longitudinal muscle contractions
Authors: Sarna S. K.
Published: December 2017

The patterns of longitudinal muscle contractions of the stomach and the small intestine and their relationship with circular muscle contractions during the fasting and the fed state were investigated in conscious dogs. In the stomach, the longitudinal muscle contracted in a 1:1 relationship with the circular muscle contractions. There was no significant difference between the frequency, duration, and time of onset of gastric longitudinal and circular muscle contractions, and their amplitudes were significantly correlated with each other. In the small intestine when the circular muscle contracted, the longitudinal muscle exhibited passive elongation during the fasting and the fed state. There was no significant difference between the onset, duration, and frequency of small intestinal circular muscle contractions and the passive longitudinal muscle elongations; their amplitudes were strongly correlated with each other. During a circular muscle giant migrating contraction, the longitudinal muscle exhibited a monophasic contraction, initially a contraction followed by passive elongation or a pure passive elongation. During a retrograde giant contraction, the longitudinal muscle exhibited only a pure monophasic contraction or a contraction-elongation complex. These data suggest that the enteric nerves in the small intestine innervate the two muscle layers in a reciprocal fashion and those in the stomach in a complementary fashion.
Nitric oxide donors reduce the rise in reperfusion-induced intestinal mucosal permeability
Authors: Payne D. , Kubes P.
Published: December 2017

Recent data have demonstrated that inhibition of nitric oxide synthesis exacerbated the mucosal injury associated with reperfusion of the postischemic intestine. In this study, using a feline 1-h intestinal ischemia followed by reperfusion model, we tested the possibility that exogenous sources of nitric oxide may prevent the reperfusion-induced mucosal barrier disruption and examined the mechanisms involved. Mucosal barrier integrity was assessed by determining 51Cr-EDTA clearance from blood to lumen. Intestinal blood flow and resistance were also determined. Reperfusion after 1 h of ischemia significantly increased 51Cr-EDTA clearance (0.05 +/- 0.01 to 0.35 +/- 0.07 ml.min-1.100 g-1) and decreased intestinal blood flow by 50%. Exogenous sources of nitric oxide including SIN-1, CAS-754, and nitroprusside as well as exogenous L-arginine all reduced reperfusion-induced mucosal barrier dysfunction without improving intestinal blood flow. Inhibition of endogenous nitric oxide with NG-nitro-L-arginine methyl ester between 1 and 2 h of reperfusion further augmented the rise in mucosal permeability associated with ischemia-reperfusion. Addition of the permeable analogue of guanosine 3',5'-cyclic monophosphate, 8-bromoguanosine 3',5'-cyclic monophosphate, improved reperfusion-induced intestinal blood flow significantly but did not provide protection against mucosal barrier disruption associated with the first hour of ischemia-reperfusion. Exogenous sources of nitric oxide can reduce reperfusion-induced mucosal barrier dysfunction independent of alterations in intestinal blood flow.
Peripheral vascular neuroeffector mechanisms in experimental cholestasis
Authors: Jacob G. , Said O. , Finberg J. , Bomzon A.
Published: December 2017

Jaundiced patients have systemic hypotension and are more susceptible to hemorrhagic shock than nonjaundiced individuals. We have hypothesized that the mechanism whereby these cardiovascular complications arise is linked to a disturbance of the vascular neuroeffector process in the cardiovascular system. With the use of 3-day bile duct-manipulated (sham-operated) and bile duct-ligated rats, we have evaluated alpha-adrenoceptor function and amine uptake using in vivo and in vitro techniques. Blunted pressor responsiveness to norepinephrine, electrical stimulation, and the alpha 1-adrenoceptor agonists, methoxamine and phenylephrine, was observed in the bile duct-ligated pithed rats. In contrast, normal responsiveness to BHT-933 and clonidine, the alpha 2-adrenoceptor agonists, was seen in these animals. The uptake 1 blocker, cocaine, caused potentiation of equal magnitudes of the pressor responsiveness to electrical stimulation and norepinephrine in the sham-operated and bile duct-ligated pithed rats. In aortic rings prepared from the bile duct-ligated rats, blunted in vitro vascular reactivity to norepinephrine and the same alpha 1-adrenoceptor agonists was seen. Bile duct ligation had no effect on norepinephrine uptake or its kinetics in stressed and unstressed arterial rings and portal veins. We have thus concluded that bile duct ligation induces a defect in the functional expression of cardiovascular alpha 1-adrenoceptors without any effects on the activity of alpha 2-adrenoceptors or norepinephrine uptake.
Partial agonism by gastrin for a cholecystokinin receptor mediating pepsinogen secretion
Authors: Tang L. H. , Miller M. D. , Goldenring J. R. , Modlin I. M. , Hersey S. J.
Published: December 2017

Isolated gastric glands from rabbit were used to characterize the functional cholecystokinin (CCK)-like peptide receptors that mediate pepsinogen secretion. Pepsinogen secretion was stimulated by both CCK octapeptide sulfate (CCK-8) and A-71378, a selective CCK-A-type receptor agonist, with similar mean effective doses (1.0 and 0.8 nM, respectively). Compared with CCK-8, gastrin-17 (G-17-I) showed reduced potency and only partial efficacy for stimulation of pepsinogen secretion while inhibiting the maximal CCK-8-stimulated response. The nonpeptide inhibitors, asperlicin and L-364,718, inhibited pepsinogen secretion with identical pA2 values for antagonism of both CCK and gastrin, indicating that both peptides interact with the same functional receptor. Specific binding of [3H]CCK-8 to isolated chief cell membranes was displaced fully by both CCK and gastrin, indicating full receptor occupancy by both peptides. A novel synthetic peptide analogue, pseudogastrin [(Glu)5-Ala-Tyr-Nle-Gly-Trp-Nle-Asp-Phe-NH2], was used to investigate the structural basis for the lower potency and efficacy of G-17-I. The potency of CCK and gastrin analogues for pepsinogen secretion was found to be dependent on both sulfation of a tyrosine residue and the position of the tyrosine residue relative to the COOH-terminal phenylalanine amide. The efficacy appears to be determined partially by the extended NH2-terminal sequence of G-17-I. The results of the present study are interpreted to show that pepsinogen secretion is mediated by a CCK-A-type receptor and gastrin acts at the same receptor as a partial agonist.
Potassium current in circular smooth muscle of human jejunum activated by fenamates
Authors: Farrugia G. , Rae J. L. , Sarr M. G. , Szurszewski J. H.
Published: December 2017

Thirty-eight cells, freshly isolated from circular smooth muscle of normal human jejunum obtained from nine patients undergoing weight-reduction surgery for morbid obesity, were patch clamped using a perforated patch-clamp technique. A highly potassium-selective voltage-dependent outward current was present in all cells. The current was carried by a 220-pS channel that activated near -75 mV and reached unit open probability at about +10 mV. Blockade of the current by quinidine (50 microM) and tetraethylammonium (25 mM) was accompanied by membrane depolarization to 0 to -3 mV, suggesting that this current was the major determinant of the membrane potential. Flufenamic and mefenamic acid at concentrations comparable with blood levels reached when these drugs are used in clinical therapy as nonsteroidal anti-inflammatory agents, activated the potassium outward current and hyperpolarized the membrane potential. The shift in the membrane potential for 250 microM flufenamic acid was -36 +/- 24 (SD) mV. Activation was rapid (seconds) and reversible. It was concluded that normal human jejunal circular smooth muscle cells have a highly potassium-selective outward current, which is the major determinant of the membrane potential and which is activated by fenamates.
Guinea pig gallbladder and pancreas possess identical CCK-A receptor subtypes: receptor cloning and expression
Authors: De Weerth A. , Pisegna J. R. , Wank S. A.
Published: December 2017

Cholecystokinin (CCK) receptors mediate pancreatic acinar secretion and gallbladder contraction. Pharmacological and functional studies in pancreas and gallbladder demonstrate a CCK-A receptor subtype in both tissues. However, some pharmacological studies and affinity cross-linking studies of CCK receptors on pancreatic acini and gallbladder suggest that these two tissues possess two different subtypes of the CCK-A receptor. We cloned these receptors in guinea pig using a cDNA clone of the CCK-A receptor from rat pancreas. The guinea pig gallbladder CCK-A receptor was cloned by hybridization screening of a gallbladder cDNA library using a cDNA probe from the rat CCK-A receptor coding region. The guinea pig pancreas CCK-A receptor cDNA was cloned via the polymerase chain reaction using primers corresponding to the guinea pig gallbladder CCK-A receptor 5'- and 3'-noncoding regions. CCK-A receptor clones from guinea pig pancreas and gallbladder had identical nucleotide sequences, which were 80% homologous to the rat CCK-A receptor cDNA sequence. The deduced amino acid sequence from guinea pig CCK-A receptors was 89% homologous to the rat CCK-A receptor sequence. Dose-inhibition binding studies of transiently expressed receptors by CCK agonists and antagonists exhibited a CCK-A receptor pharmacologically similar to the rat CCK-A receptor. These studies indicate that the CCK-A receptors in guinea pig pancreas and gallbladder are identical and do not support previous proposals that they may represent different receptor subtypes.
Characterization of intestinal gamma-glucoamylase deficiency in CBA/Ca mice
Authors: Quezada-Calvillo R. , Senchyna M. , Underdown B. J.
Published: December 2017

In previous work, we found that CBA/Ca mice display only 20% of the maltase activity present in other mouse strains. In this study, we characterized more fully the maltase deficiency in CBA/Ca mice. Virtually all of the intestinal maltase activity of CBA/Ca mice was inactivated at 50 degrees C, indicating that it was due only to the sucrase-isomaltase complex. High-performance liquid chromatographic analysis revealed that CBA/Ca mice had undetectable maltase activity displaying the molecular mass characteristic of murine gamma-glucoamylase (gamma-GA) (530 kDa). Gel electrophoretic analysis confirmed that CBA/Ca mice lacked maltase activity with molecular mass of 530 kDa corresponding to gamma-GA. Two-dimensional electrophoretic analysis revealed that the gamma-GA deficiency in CBA/Ca mice was due to the failure to synthesize the enzyme and not to the synthesis of an inactive protein. gamma-GA maltase activity could not be induced in CBA/Ca mice by a diet rich in starch, whereas the activity of other disaccharidases were readily increased. gamma-GA-deficient CBA/Ca mice appear to lack any gross metabolic abnormality resulting from this defect.