bluuebunny/crossref_metadata_2025 huggingface dataset:
Glycogenolytic effect of adenosine involves ATP from hepatocytes and eicosanoids from Kupffer cells
Authors: Nukina S. , Fusaoka T. , Thurman R. G.
Published: December 2017

In the perfused liver, infusion of adenosine (50 microM) caused an increase in portal pressure and glucose output as well as a brief increase in oxygen uptake followed by a transient decrease within 1 min. Half-maximal glycogenolytic effect was observed with approximately 20 microM adenosine, and the stimulation was maximal at concentrations > 50 microM. The effect of adenosine was blocked when Kupffer cells were destroyed with gadolinium chloride treatment (10 mg/kg iv), supporting the hypothesis that eicosanoid release from Kupffer cells participates in the effect of adenosine in the liver. Although adenosine has been reported to increase eicosanoid release from perfused liver (S. vom Dahl, M. Wettstein, W. Gerok, and D. Hussinger, Biochem. J. 270: 39-44, 1990), in this study adenosine failed to stimulate prostaglandin release from cultured Kupffer cells at concentrations ranging from 1 microM to 1 mM, casting doubt on the hypothesis that Kupffer cells are totally responsible for the effect of adenosine. In contrast, adenosine increased ATP transiently from 4 to 15 nM in effluent from perfused livers concomitant with a transient increase in carbohydrate output and portal pressure. To assess which type of hepatic cells released ATP after addition of adenosine, parenchymal, Kupffer, and endothelial cells were isolated and incubated with adenosine. Adenosine increased ATP concentrations in culture media of parenchymal cells but not from Kupffer or endothelial cells. Furthermore, ATP stimulated prostaglandin release from cultured Kupffer cells, whereas ATP (10 microM) infusion caused glucose release with kinetics similar to adenosine in perfused livers, an effect that was blocked by destroying Kupffer cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of sugars and amino acids on amphibian intestinal ClŐ transport and intracellular Na+, K+, and ClŐ activity
Authors: White J. F. , Burnup K. , Ellingsen D.
Published: December 2017

Pages G109–G117L: J. F. White, K. Burnup, and D. Ellingsen. “Effect of sugars and amino acids on amphibian intestinal Cl- transport and intracellular Na+, K+, and Cl, activity.” Page G109 (abstract, 20th line): the sentence that reads “Galactose and valine each reduced intracellular Na Activity (agrNai) markedly, whereas glucose increased agrNai only slightly” should read “Galactose and valine each increased intracellular Na activity (agrNai) markedly, whereas glucose increased agrNai only slightly.”
Nitric oxide production regulates cGMP formation and calcium influx in pancreatic acinar cells
Authors: Gukovskaya A. , Pandol S.
Published: December 2017

Guanosine 3',5'-cyclic monophosphate (cGMP) rise is one of the early events in neurotransmitter or hormone-induced cascade of reactions in pancreatic acinar cells. The mechanism of agonist-stimulated guanylyl cyclase activation in these cells remains, however, unknown. In the present work, mechanisms of cGMP rise, as well as of Ca2+ influx, induced by carbachol were studied on acinar cells isolated from rat and guinea pig pancreas. In both types of acinar cells, blocking nitric oxide (NO) production by inhibitors of NO synthase, NG-monomethyl-L-arginine (L-NMMA) or NG-nitro-L-arginine, abolished carbachol-induced cGMP rise in a dose-dependent manner. The inhibition was reversed by addition of excess L-arginine. L-NMMA also caused inhibition of the basal cGMP level, suggesting a role for NO in cGMP homeostasis in resting cells. Carbachol was found to increase [3H]arginine conversion to [3H]citrulline. This conversion was inhibited by L-NMMA. By contrast, inhibition of carbon monoxide production by Zn-protoporphyrin did not affect carbachol-stimulated cellular cGMP levels. There was no increase in cellular cGMP levels in response to exogenous arachidonic acid (AA). Blocking of lipoxygenase oxidation of AA by nordihydroguaiaretic acid did not produce any changes in carbachol-induced cGMP rise. Indomethacin, a cyclooxygenase inhibitor, increased basal cGMP level through L-NMMA-sensitive mechanism. Blockade of NO production inhibited carbachol-induced increase in 45Ca2+ uptake in both guinea pig and rat acinar cells. The concentration-response curves for inhibition by L-NMMA of 45Ca2+ uptake and cGMP formation were superimposable. L-NMMA also suppressed stimulation of Mn2+ quenching by carbachol in fura 2-loaded acini.(ABSTRACT TRUNCATED AT 250 WORDS)
Analysis of the role of 5-HT in the enteric nervous system using anti-idiotopic antibodies to 5-HT receptors
Authors: Wade P. R. , Tamir H. , Kirchgessner A. L. , Gershon M. D.
Published: December 2017

The effects of anti-idiotypic antibodies (alpha-id) that recognize serotonin [5-hydroxytryptamine (5-HT)] receptors on myenteric neurons of the guinea pig small intestine were characterized electrophysiologically, and alpha-id binding sites were located immunocytochemically. Initial applications of the alpha-id mimicked each of three actions of 5-HT: a rapid depolarization, associated with a fall in input resistance (Rin), which was inhibited by the 5-HT3 antagonists tropisetron (> or = 1 microM) and renzapride (100 microM); a slow membrane depolarization, associated with increased Rin, that was inhibited by the 5-HT1P antagonist renzapride but was unaffected by a 5-HT4 blocking concentration of tropisetron (10 microM); and a hyperpolarization, associated with decreased Rin, that was antagonized by the 5-HT1A inhibitor NAN-190. Cross-desensitization was observed between responses to 5-HT and the alpha-id. After exposure to the alpha-id, subsequent responses to the alpha-id, 5-HT, and stimulus-evoked slow excitatory postsynaptic potentials were antagonized; however, responses to carbachol and substance P were unaffected. The alpha-id thus specifically inhibits the effects of endogenously released and exogenously applied 5-HT. The alpha-id bound to sites on myenteric and submucosal neurons and a subepithelial nerve plexus. Binding of the alpha-id was blocked by 5-HT1P-, 5-HT3-, and 5-HT4-specific antagonists. We concluded that the alpha-id binds selectively to all known subtypes of 5-HT receptor in the enteric nervous system and is thus useful for investigating the gastrointestinal function of 5-HT.
Osmotic water flow pathways across Necturus gallbladder: role of the tight junction
Authors: Loeschke K. , Bentzel C. J.
Published: December 2017

To explore the quantitative significance of passive water flow through tight junctions of leaky epithelia, transepithelial water flow rates were measured in Necturus gallbladder mounted in chambers. Osmotic flows generated by raffinose gradients were asymmetrical with the greater flow in the mucosal-to-serosal direction. In tissue fixed in situ, intercellular spaces were dilated during mucosal-to-serosal flow and closed during serosal-to-mucosal flow. Tight junctions were focally separated (blistered), which correlated with the magnitude of mucosal-to-serosal flow. Blisters were not observed during serosal-to-mucosal flow or in nontransporting gallbladders. In freeze-fracture replicas, blisters appeared as pockets between intramembranous strands. Protamine, which decreases electrical conductance and increases depth and complexity of the tight junction, reduced osmotic water flow by approximately 30% in the mucosal-to-serosal direction (100 mosmol/kg gradient) without altering serosal-to-mucosal flow. We suggest that in the steady state, at least 30% of osmotically driven water passes transjunctionally in the mucosal-to-serosal direction, but flow is transcellular in the serosal-to-mucosal direction. Directionally divergent pathways may account for flow asymmetry.
Reoxygenation injury in isolated rat hepatocytes: relation to oxygen free radicals and lipid peroxidation
Authors: Caraceni P. , Rosenblum E. R. , Van Thiel D. H. , Borle A. B.
Published: December 2017

Oxygen free radical (OFR) formation and lipid peroxidation (LP) were measured in freshly isolated perfused rat hepatocytes during 2-h reoxygenation after 2.5 h of anoxia. Superoxide anions and hydrogen peroxide (H2O2) were detected by enhanced chemiluminescence. LP and cell damage were assessed by measuring malondialdehyde (MDA) and lactic dehydrogenase (LDH) release, respectively. During anoxia, the chemiluminescence decreased to background levels and MDA remained constant, whereas LDH release increased progressively to 168 +/- 22 mU/min in 2.5 h. During reoxygenation after a 2.5-h period of anoxia, superoxide formation increased rapidly to 125 +/- 16 nA and then it declined progressively toward the control level. At the same time, H2O2 production exhibited a biphasic pattern with an initial peak reaching 78 +/- 16 nA at 15.5 +/- 1 min, followed by a slower increase to 92 +/- 14 nA during the 2nd h. LDH release increased from 168 +/- 22 to 286 +/- 32 mU/min in the first 30 min of reoxygenation and then declined toward the control rate during the 2nd h. MDA release increased continuously from 1.16 +/- 0.18 to 7.75 +/- 0.74 pmol/min. OFR generation occurred 15-30 min before the peak rise in LDH. Moreover, after shorter periods of anoxia (1-2 h), hepatocytes produced measurable amount of OFR but without a significant increase in LDH release. These results demonstrate that 1) isolated liver parenchymal cells generate measurable amounts of superoxide anions and of H2O2 during reoxygenation after 1-2.5 h of anoxia, 2) lipid peroxidation follows the formation of OFR, and 3) reoxygenation injury is correlated to OFR generation but not to lipid peroxidation.
Smooth muscle cells from guinea pig stomach possess high-affinity galanin receptors that mediate relaxation
Authors: Gu Z. F. , Pradhan T. K. , Coy D. H. , Jensen R. T.
Published: December 2017

Galanin-like immunoactivity occurs in nerves and plexi in muscle layers throughout gastrointestinal tract including the stomach. Galanin can affect gastric emptying and contraction or relaxation of gastric muscle in different species. The aim of this study was to investigate the direct effect of galanin on dispersed gastric smooth muscle cells and to characterize any galanin receptors that mediated any effect. Dispersed gastric smooth muscle cells were prepared from guinea pig stomach by collagenase digestion. Porcine galanin (p-galanin; 1 microM) did not stimulate contraction when present alone; however, p-galanin (1 microM) inhibited carbachol-induced contraction with a half-maximal effect at 7 nM. p-Galanin (1 microM) increased cellular adenosine 3',5'-cyclic monophosphate (cAMP) content by 10 s and caused a maximal increase of 80% over basal. 125I-galanin (porcine) bound to dispersed cells in a time- and temperature-dependent manner. Binding was saturable, reversible, and specific. Binding of 125I-galanin was inhibited almost equally by porcine and rat galanin (Ki = 6-8 nM) but was not inhibited by the galanin-associated peptide [preprogalanin-(108-123)]. The fragment galanin-(1-16) was equally potent to rat galanin; however, the fragment galanin-(9-29) was 56-fold less potent (Ki = 370 nM). Computer analysis demonstrated there were two binding sites for p-galanin on gastric smooth muscle cells, a high-affinity site (Kd = 2.6 nM) with low capacity (Bmax = 175 fmol/mg protein) and a low-affinity site (Kd = 150 nM) with large capacity (Bmax = 3,611 fmol/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)
Somatostatin inhibits CCK release by inhibiting secretion and action of CCK-releasing peptide
Authors: Herzig K. H. , Louie D. S. , Owyang C.
Published: December 2017

We hypothesized that somatostatin exerts its inhibitory action on cholecystokinin (CCK) release and pancreatic secretion by inhibiting the secretion and/or action of a CCK-releasing peptide (CCK-RP) secreted from the small intestine. Our studies demonstrated that intravenous infusion of somatostatin (25 micrograms.kg-1.h-1) completely inhibited the increase in amylase output evoked by diversion of bile-pancreatic juice and 80 +/- 10% of the increase in plasma CCK. Intraduodenal administration of concentrated intestinal perfusate containing the CCK-RP collected from a donor rat with bile-pancreatic juice diversion raised amylase output by 2.3-fold and elevated plasma CCK levels to 7 +/- 0.8 pM in a recipient rat. The stimulatory effect of the concentrated intestinal washings was abolished when the "donor" rat was pretreated with somatostatin. In addition, in somatostatin-treated "recipient" rats, intraduodenal administration of intestinal washings containing CCK-RP also failed to elicit an increase in plasma CCK and amylase secretion. Furthermore, using duodenal mucosal explants, we demonstrated that the inhibitory action of somatostatin on CCK release evoked by CCK-RP was antagonized by pretreatment with pertussis toxin. These observations strongly suggest that somatostatin inhibits feedback regulation of pancreatic enzyme secretion by inhibiting both the secretion and action of CCK-RP.
Pancreatic tumoral cell line AR42J: an amphicrine model
Authors: Christophe J.
Published: December 2017

AR42J cells derive from azaserine-induced malignant nodules from the rat pancreas. They differ from normal acinar cells for at least three reasons: 1) they proliferate rapidly; 2) they synthesize, store, and secrete digestive enzymes but the regulation of their exocrine function is abnormal, from the emergence of atypical receptors (e.g., cholecystokinin octapeptide type B and pituitary adenylate cyclase-activating polypeptide type I receptors) to unusual inositol phosphate metabolism and cytoskeleton disorganization; and 3) they possess an added neuroendocrine-regulated pathway characterized by voltage-sensitive ionic currents, post-translational processing of peptidic prohormones (and possibly autocriny), and the release of small neurotransmitters (gamma-aminobutyric acid, glycine, and glutamic acid). These amphicrine cells represent, therefore, a cancerous version of the primordial pancreatic ductular epithelium. Dexamethasone favors their differentiation toward the exocrine phenotype. The mitogenic pathway is favored by the occupancy of receptor tyrosine kinases, adenosine 3',5'-cyclic monophosphate, ornithine decarboxylase expression, and Na(+)-H+ exchange. Somatostatin opposes proliferation through protein phosphatases.
ET-1 induced alterations of hepatic microcirculation: sinusoidal and extrasinusoidal sites of action
Authors: Bauer M. , Zhang J. X. , Bauer I. , Clemens M. G.
Published: December 2017

Using epifluorescence microscopy, we investigated the dynamic changes in hepatic sinusoidal hemodynamics in vivo during continuous infusion of endothelin-1 (ET-1) in pentobarbital-anesthetized rats. ET-1 was infused for 20 min at rates of 2 or 10 pmol/min either systemically or into the portal vein, followed by a 90-min recovery period. In contrast to systemic application of ET-1 that did not cause a consistent hepatic microvascular effect, we observed two different patterns of microcirculatory alterations during portal application. Infusion of 2 pmol/min elicited a rapid, reversible decrease in sinusoidal diameter that was paralleled by a slight increase in red cell velocity, resulting in conservation of volumetric flow and sinusoid density. Infusion of 10 pmol/min resulted in a biphasic narrowing followed by transient increase in sinusoidal diameter and a profound and lasting decrease in red cell velocity, leading to an almost complete cessation of hepatic microvascular blood flow. These results indicate that ET-1 is a potent constrictor in the liver microcirculation in vivo and acts at both extrasinusoidal and sinusoidal sites, although the sinusoidal sites appear to be more sensitive to lower concentrations.
Protein-mediated transfer of fluorescent-labeled phospholipids across brush border of rabbit intestine
Authors: Zhang Z. , Nichols J. W.
Published: December 2017

Monoacyl and diacyl phospholipids labeled with the fluorescent probe 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) were used to measure the rate of phospholipid transfer between artificial large unilammelar vesicles and rabbit intestine brush-border membrane vesicles (BBMV). This assay demonstrated that transfer into and out of BBMV occurred in two kinetic phases. The fast rate of transfer resulted from interbilayer transfer between the outer membrane leaflets. The slower rate resulted from transmembrane transfer across the BBMV. Treatment of the BBMV with the protease pronase E and with the histidyl reagent diethylpyrocarbonate inhibited the rate of transmembrane transfer. Phospholipids containing one or two acyl chains and a wide range of head-group structures were transported across the membranes with rates that increased as a direct function of their water solubility. These data demonstrated the existence of a protein transporter in the intestinal brush border that functions to absorb slightly water-soluble lysophospholipids and short-chain diacyl phospholipids without redistributing the highly water-insoluble long-chain diacyl phospholipids between the outer and inner leaflets of the brush-border membrane.
Role of prostaglandins in angiotensin II-induced gastric vasoconstriction
Authors: Wood J. G. , Yan Z. Y. , Cheung L. Y.
Published: December 2017

The purpose of our study was to examine the role of prostaglandins in angiotensin II (ANG II)-induced gastric vasoconstriction. ANG II produced statistically significant, dose-related increases in vascular resistance of a mechanically perfused ex vivo stomach segment of chloralose-anesthetized dogs. We next examined the effect of cyclooxygenase inhibitors on responses to ANG II. Indomethacin (10 mg/kg), which blocked the vasodilator response to intra-arterial arachidonic acid, augmented the maximal increase in perfusion pressure during ANG II infusion. Similar results were found using a different cyclooxygenase inhibitor, meclofenamic acid. In the final experiments we used an enzyme immunoassay to measure 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha) plasma concentrations. ANG II produced dose-related increases in gastric venous but not arterial levels of 6-keto-PGF1 alpha, the major metabolite of prostacyclin. Our results are consistent with the hypothesis that release of vasodilatory prostaglandins attenuates the vasoconstrictor response to ANG II in the gastric microcirculation.
Multistep mechanism of polarized Ca2+ wave patterns in hepatocytes
Authors: Nathanson M. H. , Burgstahler A. D. , Fallon M. B.
Published: December 2017

The spatial organization of cytosolic Ca2+ (Ca2+i) signals is thought to be important for regulation of cell function. In epithelial cells, the involvement of inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ release in evoking Ca2+i signals is appreciated, but the location of IP3-sensitive Ca2+ stores and the role of Ca(2+)-induced Ca2+ release (CICR) for Ca2+ signaling are less defined. Here, we demonstrate that IP3 receptors are localized to the apical region in hepatocytes. We also show that hormone-induced Ca2+i waves propagate across the cell at a rate that depends on mobilization of Ca2+ stores that are sensitive to caffeine, ryanodine, and dantrolene, and that these agents, at concentrations that inhibit CICR, decrease the magnitude of Ca2+i signals. Furthermore, Ca2+i wave speed is not reduced in Ca(2+)-free medium. These findings suggest that Ca2+i signals in epithelial cells begin as apical-to-basal Ca2+i waves that result from sequential release of Ca2+, first from IP3-sensitive stores in the apex and then from Ca(2+)-sensitive stores distributed across the remainder of the cell.
Nitric oxide modulates hepatic vascular tone in normal rat liver
Authors: Mittal M. K. , Gupta T. K. , Lee F. Y. , Sieber C. C. , Groszmann R. J.
Published: December 2017

This study investigated whether nitric oxide (NO) plays a role in the intrahepatic portal circulation in normal rat livers perfused in situ. N omega-nitro-L-arginine (NNA), a specific NO biosynthesis inhibitor, significantly increased baseline portal pressure compared with controls (P < 0.05). Concentration-effect curves to norepinephrine (NE) were performed. Perfusate flow was maintained as constant, and perfusion pressure was continuously measured. NNA markedly enhanced the responsiveness to NE. This effect was abolished by the addition of L-arginine, a specific NO substrate. Presence of indomethacin did not alter the response to NE. The response to NE in the presence of indomethacin and NNA was significantly more than the response to NE in the presence of NNA alone. In vivo, intraportal infusion of NNA significantly enhanced the portal pressure compared with vehicle. This study demonstrates that NO contributes to the basal vascular tone and attenuates the response to NE in intrahepatic portal vascular bed of normal rats. These results support a functional role of NO in the regulation of the intrahepatic portal circulation in normal rats. This study also suggests a synergistic, albeit limited, role of prostacyclin in the intrahepatic circulation.
Regulation of cholecystokinin secretion by ATP-sensitive potassium channels
Authors: Mangel A. W. , Prpic V. , Snow N. D. , Basavappa S. , Hurst L. J. , Sharara A. I. , Liddle R. A.
Published: December 2017

The relationship of potassium channel activity to the secretion of cholecystokinin (CCK) was evaluated in STC-1 cells, an intestinal CCK-secreting cell line. Patch-clamp and 86Rb efflux studies showed that an ATP-sensitive potassium channel was endogenously expressed in STC-1 cells. Furthermore, channels are present in sufficient number to significantly modulate whole cell potassium permeability after either channel activation or closure with diazoxide (100 microM) or disopyramide (200 microM), respectively. Inhibition of channel activity with glucose (5-20 mM) was found to depolarize the plasma membrane, increase cytosolic calcium levels, and stimulate CCK release. Glucose-mediated release of CCK, as well as the increase in cytosolic calcium, was inhibited by the calcium channel blocker diltiazem (10 microM). It is concluded that intestinal secretion of CCK may be tonically controlled by activity of basally active ATP-sensitive potassium channels, and after inhibition of channel activity, calcium-dependent CCK secretion is stimulated.
Gastrin effects on isolated rat enterochromaffin-like cells in primary culture
Authors: Prinz C. , Scott D. R. , Hurwitz D. , Helander H. F. , Sachs G.
Published: December 2017

The hormone gastrin stimulates acid secretion by releasing histamine from gastric enterochromaffin-like (ECL) cells and induces ECL cell proliferation in vivo. This study uses a > 90% pure ECL cell preparation in culture to compare gastrin effects on histamine release, histidine decarboxylase (HDC) activity, and DNA synthesis. Gastrin and the cholecystokinin octapeptide (CCK-8, nonsulfated) induced histamine release from ECL cells (24-96 h of primary culture) within 5 min of incubation [concentration eliciting 50% of maximal response (EC50), 4 and 2 x 10(-11) M, respectively]. The CCK-B antagonist L-365,260 inhibited this effect [concentration inhibiting 50% of maximal response (IC50), 2 x 10(-8) M], whereas the CCK-A antagonist L-364,718 (10(-8) M) and the tyrosine kinase inhibitor genistein (10(-4) M) had no effect. Histamine release was associated with a biphasic elevation of intracellular Ca2+. Gastrin stimulated HDC activity two- to threefold after 60 min of incubation (EC50, 10(-10) M). Gastrin also increased DNA synthesis in ECL cells, with an EC50 of 1.7 x 10(-12) M as measured by the incorporation of 5-bromo-2'-deoxyuridine (BrdU). Positive nuclear immunostaining increased two- to threefold in up to 20% of ECL cells after 48-96 h of incubation. This effect was inhibited by L-365,260 (IC50, 5 x 10(-9) M) and by genistein (10(-4) M) but was not altered by L-364,718 (10(-8) M). The antisecretory drugs omeprazole, lansoprazole, and pantoprazole did not affect BrdU incorporation in isolated ECL cells. In conclusion, acute and chronic gastrin effects on the ECL cell are mediated via CCK-B receptors but differ in apparent receptor affinity and signal transduction pathways.
Nerve growth factor promotes neurite outgrowth in guinea pig myenteric plexus ganglia
Authors: Mulholland M. W. , Romanchuk G. , Lally K. , Simeone D. M.
Published: December 2017

Nerve growth factor (NGF) has important developmental actions in both central and peripheral nervous systems. Primary cultures of neonatal guinea pig myenteric plexus ganglia were used to examine the ability of NGF to stimulate morphological development in enteric neurons. NGF, in the presence of a serum-free medium, produced dose-dependent increases in neurite density, significant at 1 ng/ml and maximal at 100 ng/ml (4.5-fold increase vs. control). Maximum neurite length was also significantly increased at 1 ng/ml, with maximal effects at 100 ng/ml. Coincubation of NGF (50 ng/ml) with monoclonal NGF antibodies abolished increases in both neurite density (128 +/- 19 processes/mm for control, 369 +/- 19 for NGF, 183 +/- 28 for NGF+monoclonal antibodies) and neurite length. Exposure of enteric neurons to low concentrations of NGF (1 ng/ml) was also associated with increased mRNA levels for cytoskeletal genes. alpha-Tubulin mRNA levels were increased 3.9 +/- 0.7 times basal at 48 h. mRNA levels for microtubule-associated protein 2 were increased threefold at 48 h of NGF incubation. NGF demonstrates activities in cultured enteric ganglia that stimulate morphological development.
Cellular mechanisms and physiological implications of quantal Ca2+ release in pancreatic acinar cells
Authors: Rutherford R. E. , Schoeffield-Payne M. , Pandol S. J.
Published: December 2017

Previous studies in pancreatic acini demonstrated that submaximal concentrations of agonist release only a portion of Ca2+ from the intracellular pool during the first few seconds of stimulation. Despite continued stimulation, no further release of pool Ca2+ takes place. This process has been termed quantal release. Previous hypotheses have proposed that quantal release results from varying sensitivities of the intracellular pool to inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ release. The purpose of the present experiments was to further characterize the cellular mechanism of quantal release and to determine the role of quantal release in pancreatic enzyme secretion. The results indicate that the phenomenon of quantal calcium release is not due to varying sensitivities of the intracellular Ca2+ stores to IP3. Quantal release results from both an intrinsic property of the IP3 receptor, which causes it to transport Ca2+ transiently, and from the transient nature of the increase in IP3 generated by submaximal agonist concentration. With this mechanism, sequential additions of physiological concentrations of agonist cause transient increases in intracellular Ca2+ concentration leading to bursts of enzyme secretion.
Neuroimmune communication in the submucous plexus of guinea pig colon after sensitization to milk antigen
Authors: Frieling T. , Cooke H. J. , Wood J. D.
Published: December 2017

We investigated electrical and synaptic behavior of neurons in the colonic submucous plexus during exposure to beta-lactoglobulin in guinea pigs sensitized by ingestion of milk. Microelectrodes were used to record electrical and synaptic behavior in neurons from milk-sensitized and nonsensitized age-matched animals during exposure to beta-lactoglobulin. Neurons in sensitized animals were hyperexcitable. Application of the histamine H2 antagonist cimetidine reversed the hyperexcitability, suggesting endogenously released histamine as one of the responsible factors. Antigenic exposure suppressed stimulus-evoked nicotinic cholinergic fast excitatory postsynaptic potentials (EPSPs). This was blocked by the selective histamine H3 antagonist burimamide. Suppression of the EPSPs resulted from presynaptic inhibition of acetylcholine release. Increased neuronal excitability and suppression of synaptic transmission was only found in milk-sensitized intestine, not in the intestine from age-matched nonsensitized animals. We concluded that signaling from mucosal mast cells to the enteric nervous system is important in colonic defense against antigenic threats. Histamine is a paracrine messenger in the communication network.
Brush-border disaccharidase synthesis in infant pigs measured in vivo with [2H3]leucine
Authors: Dudley M. A. , Jahoor F. , Burrin D. G. , Reeds P. J.
Published: December 2017

Conscious unrestrained piglets were fasted overnight and infused intravenously with [2H3]leucine for 6 h. Sucrase isomaltase and lactase phlorizin hydrolase were immunoprecipitated from jejunal mucosal membranes, and the immunoprecipitates were electrophoresed on polyacrylamide gels. Bands corresponding to the pro and mature isoforms of both enzymes were acid hydrolyzed. [2H3]leucine isotopic enrichment was measured by gas chromatography-mass spectrometry using negative chemical ionization. Plasma leucine reached isotopic steady state within 90 min. The isotopic enrichment of mucosal leucine was 73% of that of plasma leucine. The high mannose and complex glycosylated forms of prolactase were in isotopic equilibrium, and their isotopic enrichment was 94% of mucosal leucine. The fractional synthesis rates of total and membrane protein were 0.45 and 0.65 days-1, whereas the processing rates of mature lactase, sucrase, and isomaltase were 0.90, 0.23, and 0.21 days-1, respectively. Approximately 65% of the label in the sucrase isomaltase immunoprecipitate was in the complex glycosylated precursor, whereas 73% of the label in lactase phlorizin hydrolase was in the mature (160 kDa) form. We conclude that the low rate of brush-border sucrase synthesis reflects a slow rate at which the complex glycosylated precursor is processed to the brush-border form.
IL-8 secretion and neutrophil activation by HT-29 colonic epithelial cells
Authors: Kelly C. P. , Keates S. , Siegenberg D. , Linevsky J. K. , Pothoulakis C. , Brady H. R.
Published: December 2017

This study examines the ability of HT-29 human colonic epithelial cells to stimulate neutrophil migration and adhesion. Interleukin-8 (IL-8), a potent neutrophil chemoattractant, was detected in conditioned media from both unstimulated (1.1 ng/ml) and IL-1 beta-stimulated (16.1 ng/ml) HT-29 cultures. Conditioned medium from IL-1 beta-exposed HT-29 cells stimulated neutrophil migration (395% of control, P < 0.01), and this effect was completely inhibited by anti-IL-8 antibody. HT-29 medium also induced shedding of neutrophil L-selectin and increased expression of neutrophil CD11/CD18 adhesion receptors. Coculture of HT-29 cells with human endothelial cell monolayers resulted in increased neutrophil transendothelial migration (169% of control, P < 0.01), which was blocked by both anti-IL-8 and anti-CD18 antibody. Northern hybridization analysis demonstrated increased levels of mRNA for IL-8 and intercellular adhesion molecule-1 (ICAM-1) in cytokine-treated HT-29 cells. Cytokine stimulation of HT-29 monolayers was also associated with increased neutrophil adhesion to these cells. Neutrophil-HT-29 cell adhesion was blocked by monoclonal antibodies to neutrophil CD18 or to ICAM-1 on the HT-29 cells (86% and 56% inhibition, respectively, P < 0.01 for both). These data suggest that IL-8 secretion by activated colonic epithelial cells may contribute to neutrophil extravasation and tissue infiltration in intestinal inflammation.
Vagovagal reflex control of digestion: afferent modulation by neural and "endoneurocrine" factors
Authors: Rogers R. C. , McTigue D. M. , Hermann G. E.
Published: December 2017

Vagovagal reflex control circuits in the dorsal vagal complex of the brain stem provide overall coordination of gastric, small intestinal, and pancreatic digestive functions. The neural components forming these reflex circuits are under substantial descending neural control. By adjusting the excitability of the differing components of the reflex, significant alterations in digestion control can be produced by the central nervous system. Additionally, the dorsal vagal complex is situated within a circumventricular region without a "blood-brain barrier." As a result, vagovagal reflex circuitry is also exposed to humoral influences, which can profoundly alter digestive functions by acting directly on brain stem neurons.
Tonic responses of canine proximal colon: effects of eating, nutrients, and simulated diarrhea
Authors: Basilisco G. , Phillips S. F. , Cullen J. J. , Chiravuri M.
Published: December 2017

Our hypothesis was that the proximal colon relaxes to accommodate flow from the ileum. Therefore, we recorded tonic responses of the canine proximal colon to flow through the ileum and colon stimulated by 1) an 840-kcal meal, 2) nutrients perfused into the ileum and colon, or 3) rapid infusion of saline into the ileum with overflow into the colon. Saline infusion was considered to be a model of diarrhea, and the effects of an antidiarrheal (morphine sulfate) were therefore assessed. Proximal colonic tone was measured with a barostat. Tone increased before and after the arrival of chyme in the ileocolonic region. Perfusion of nutrients into the ileum and colon also significantly increased (P < 0.05) colonic tone compared with equal volumes of saline. Rapid perfusion of the ileocolonic segment with saline increased colonic tone; this increase was significantly greater (P < 0.01) when preceded by morphine. In contrast to our hypothesis, tone of the canine proximal colon increased in response to ileal flow. The increase in colonic tone during the late response to food was at least partly attributable to stimulation by intraluminal contents.
Luminal dilution caused by certain mild irritants and capsaicin contributes to their gastric mucosal protection
Authors: Hatakeyama Y. , Matsuo M. , Tomoi M. , Ohtsuka M. , Shimomura K.
Published: December 2017

We have recently shown that certain mild irritants caused the increase in fluid volume in the rat stomach. The present study was conducted to investigate 1) whether standing fluid in the gastric cavity can prevent gastric mucosal injury caused by 0.6 N HCl and 2) the mechanisms by which certain mild irritants increase the gastric fluid volume. One milliliter of water administered immediately before irritants greatly inhibited gastric lesion formation. Sodium chloride and capsaicin induced a profound enhancement of gastric fluid volume, as acid mild irritants did also. Sensory denervation completely abolished the volume increase caused by capsaicin but hardly influenced that caused by mild irritants. Capsaicin increased the amount of Evans blue in the gastric fluid, but mild irritants did not. On the other hand, HCl and capsaicin significantly inhibited the emptying of phenol red. From these results, we conclude that mild irritants and capsaicin can induce volume increase that by itself is enough to afford protection through luminal dilution. Capsaicin but not mild irritants requires sensory neurons to increase the gastric fluid volume. Certain mild irritants may provide a fluid pooling effect partly by inhibiting gastric emptying.
Physiology of oropharyngeal swallow in the cat: a videofluoroscopic and electromyographic study
Authors: Kobara-Mates M. , Logemann J. A. , Larson C. , Kahrilas P. J.
Published: December 2017

The majority of animal studies of deglutition have examined electrically stimulated swallows in sedated animals. This present investigation examined oropharyngeal and cervical esophageal swallow physiology in three awake normal domestic cats using concurrent electromyography (EMG) and videofluorography (VFG). Hooked wire electrodes were surgically implanted into six oropharyngeal muscles in each cat. During collection of VFG and EMG data, each cat ate barium-impregnated cat food while the fluorography tube focused on a lateral view of the oral cavity, pharynx, and cervical esophagus. A number of significant differences in the physiology of swallowing were found between the cat and human adult. The oral stage of swallow is much longer in the cat with bolus accumulation in the valleculae. Duration and components of the pharyngeal stage of swallow are much faster, and the pharyngeal stage occurs earlier in relation to bolus passage through the cricopharyngeus. In addition, the cat exhibits a marked superior constrictor bulge at the onset of the pharyngeal contractile wave and summation of the peristaltic waves in the esophagus, whereas the human adult does not. Feline swallow physiology is more similar to that of the human infant than that of human adults.
Gut phospholipase A2 mediates neutrophil priming and lung injury after mesenteric ischemia-reperfusion
Authors: Koike K. , Moore E. E. , Moore F. A. , Kim F. J. , Carl V. S. , Banerjee A.
Published: December 2017

Intestinal ischemia-reperfusion (I/R) provokes polymorphonuclear neutrophil (PMN)-mediated lung injury via a process characterized by circulating PMN priming, pulmonary PMN sequestration, and increased microvascular leak in the lung. We found in rats subjected to intestinal I/R (ischemia 45 min and reperfusion 6 h) that 1) intestinal phospholipase A2 (PLA2) was activated during ischemia, 2) circulating PMN priming (assessed by superoxide production with N-formyl-Met-Leu-Phe) occurred after 1 h reperfusion, and 3) exaggerated 125I-labeled albumin lung leak occurred after 2 h reperfusion, compared with sham-treated animals (P < 0.05). Treatment with a PLA2 inhibitor, quinacrine, within 15 min of reperfusion reversed the exaggerated gut PLA2 activity and abrogated subsequent PMN priming and lung leak (P < 0.05). However, when quinacrine was administered after 2 h of reperfusion, circulating PMN priming and lung leak continued to evolve despite suppression of intestinal PLA2 activity. We conclude that intestinal PLA2 activation may be a prerequisite for the sequelae of circulating PMN priming and pulmonary microvascular leak observed after intestinal I/R.
Gastrin-CCK-B type receptors on human T lymphoblastoid Jurkat cells
Authors: Dornand J. , Roche S. , Michel F. , Bali J. P. , Cabane S. , Favero J. , Magous R.
Published: December 2017

The presence of specific receptors for gastrointestinal hormones on T cells and their involvement in the immune response are still matters of debate. We reported the effects of gastrin-cholecystokinin (CCK)-related peptides on J.RT3-T3.5 Jurkat cells. A single class of high-affinity binding sites (dissociation constant approximately 0.1 nM) for gastrin and CCK-8 was evident on these cells. These peptides dose-dependently induced a transient increase in intracellular Ca2+ concentration ([Ca2+]i), which was independent of extracellular Ca2-. L-365,260 was 150- to 300-fold more potent than L-364,718 to inhibit radiolabeled ligand binding or peptide-stimulated [Ca2+]i increase, confirming the gastrin-CCK-B nature of the receptor. Gastrin caused a rise in inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] level within 5 s of stimulation. Finally, gastrin increased interleukin (IL)-2 secretion in J.RT3-T3.5 cells. We conclude that 1) J.RT3-T3.5 cells possess "gastrin-CCK-B type" receptors coupled to phospholipase C activation, Ins(1,4,5)P3 formation, and Ca2+ release from intracellular Ca2+ pools, and 2) these receptors could be involved in the regulation of IL-2 production.
Involvement of capsaicin-sensitive primary afferent fibers in regulation of jejunal alanine absorption
Authors: Nassar C. F. , Barada K. A. , Abdallah L. E. , Hamdan W. S. , Taha A. M. , Atweh S. F. , Saade N. E.
Published: December 2017

Capsaicin-sensitive primary afferent fibers (CSPA) in the small intestine regulate many functions through the release of peptides and neurotransmitters. This study was undertaken to assess the role of CSPA in the regulation of jejunal alanine absorption in the rat. In a series of in vivo experiments, the effects of the sensory neurotoxin capsaicin on small intestinal alanine absorption were evaluated. In vitro experiments were also done to study its effects on alanine uptake by isolated jejunal strips and mucosal scrapings. Jejunal alanine absorption was reduced by 27% when capsaicin (160 and 800 microM) was perfused intraluminally and by 21% when it was applied topically to the cervical vagi. On the other hand, bilateral cervical vagotomy and reversible block of vagal CSPA increased alanine absorption by 29 and 41%, respectively. In vitro, capsaicin reduced alanine uptake by intestinal strips in a dose-dependent manner. Maximal inhibition (36.5%) occurred at 400 microM with the mean ineffective concentration at 87 microM. Alanine uptake by jejunal mucosal scrapings, however, was decreased only by 6.7% when incubated with 1,600 microM capsaicin. These data suggest that vagal CSPA exerts a tonic inhibitory effect on alanine absorption and that capsaicin's inhibitory effect on alanine absorption is mediated largely by the capsaicin-sensitive afferent fibers.
Organization of the crypt-villus axis and evolution of its stem cell hierarchy during intestinal development
Authors: Hermiston M. L. , Gordon J. I.
Published: December 2017

The small intestinal crypt of the adult mouse represents a model system for studying cell renewal. One or more functionally equivalent stem cells located within the crypt fuel a continuous regeneration of the gut's four principal epithelial cell lineages. These lineages differentiate during a geographically well-organized migration along the crypt-villus axis. This axis does not complete its morphogenetic program until the third postnatal week. We examined the organization of the crypt-villus axis and its stem cell hierarchy in postnatal day 1 (P1) to P28 transgenic mice. These mice contained transcriptional regulatory elements from the liver fatty acid binding protein gene linked to a human growth hormone (hGH) reporter. Adult male and female animals exhibit a striped pattern of hGH accumulation in their villus-associated epithelial cells: vertical coherent bands of wholly hGH-positive epithelial cells derived from a monoclonal crypt and vertical coherent stripes of wholly hGH-negative epithelial cells derived from an adjacent crypt extend to the apical extrusion zone of their common villus. Villus striping develops in a proximal-to-distal wave that extends from the duodenum to the jejunum by P7 and to the ileum by P14. Striping occurs as a result of a loss in the ability to support transgene expression. The decision appears to affect all cells within a stripe, irrespective of their position along the basilar-to-apical axis of a villus, suggesting that it is programmed by the nascent crypt's multipotent stem cell(s). Suppression of transgene expression traverses the crypt-villus axis more rapidly than the rate of epithelial cell migration. The boundary between stripes is very sharp and does not contain cells with transitional levels of the hGH reporter, indicating that the epithelial components of the crypt-villus axis have a higher degree of organization at this stage of development than appreciated previously.
Changes in enteric neural regulation of smooth muscle in a rabbit model of small intestinal inflammation
Authors: Goldhill J. M. , Sanders K. M. , Sjogren R. , Shea-Donohue T.
Published: December 2017

In vitro electrophysiological studies of ileal circular muscle from rabbits with ricin-induced inflammation were performed to investigate whether altered neural control or myogenic activity contributes to previously described changes in in vivo myoelectric activity. Ricin treatment increased mean slow-wave amplitude but not frequency or resting membrane potential. Prolonged electrical field stimulation evoked a hyperpolarization during the stimulus train and a depolarization on cessation of stimulation. In the presence of atropine, the depolarization was larger in ricin-treated tissue than in control tissue, showing that ileitis enhanced noncholinergic excitation. The nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester reduced the hyperpolarization in ricin-treated but not in control tissue, suggesting that inflammation increased nitric oxide-mediated inhibition. Substance P desensitization reduced noncholinergic excitation and mean slow-wave amplitude only in ricin-treated tissue, demonstrating that changes in these parameters during inflammation resulted from increased release of, or sensitivity to, tachykinins. These data suggest that acute ileitis alters tachykinin- and nitric oxide-mediated neurotransmission that may affect the normal pattern of ileal motility and/or sensory reflexes.
Extracellular heterotrimeric laminin promotes differentiation in human enterocytes
Authors: Vachon P. H. , Beaulieu J. F.
Published: December 2017

To investigate the role of laminin (Ln) and merosin (a Ln variant) in the modulation of intestinal epithelial cell differentiation, we have analyzed their functional expression as well as their potential influence during the differentiation process of Caco-2 cells, a human cell line unique in its property to differentiate into a mature enterocyte-like cell type in vitro. By indirect immunofluorescence and Western blotting, Caco-2 cells have been found to express the B1 and B2 chains of Ln, as well as a heavy approximately 350- to 370-kDa chain related to the human A chain, but not the M chain, of merosin. A gradual deposition of this A-like chain-containing Ln molecule has been observed as Caco-2 cells undergo differentiation. At the cellular level, a clear relationship between basal staining for the A chain and apical staining for the brush-border membrane enzyme sucrase-isomaltase (SI) has been observed. Human Ln, used as substratum, has been found to increase significantly the expression of SI and lactase in Caco-2 cells, whereas both Ln and human merosin have been shown to stimulate aminopeptidase N and alkaline phosphatase expression. Taken together, these data indicate that enterocytic differentiation-related gene expression is promoted by an extracellular deposition of Ln and may be susceptible to a differential modulation by variant forms of the molecule.
Effects of posture on gastric emptying of nonnutrient liquids and antropyloroduodenal motility
Authors: Anvari M. , Horowitz M. , Fraser R. , Maddox A. , Myers J. , Dent J. , Jamieson G. G.
Published: December 2017

The effects of posture on gastric emptying, intragastric distribution, and antropyloroduodenal motility after ingestion of a nonnutrient liquid have been evaluated. In seven healthy volunteers antropyloroduodenal pressures were measured for 30 min after ingestion of 150 ml of normal saline in two different positions: sitting and left lateral. Saline drinks were radiolabeled and ingested both before and after intravenous atropine (4 micrograms/kg). Rates of emptying from both the total (P < 0.05) and the proximal (P < 0.05) stomach were faster in the sitting position than in the left lateral position. There were more long (> 6 cm) antropyloric pressure waves (P < 0.05) and isolated pyloric pressure waves (P < 0.05) in the sitting position. Intravenous atropine slowed emptying in both positions (P < 0.05) and in the sitting position decreased (P < 0.05) the number of antropyloric pressure waves. After atropine, gastric emptying was also faster in the sitting compared with the decubitus position (P < 0.05), although there was no difference in antropyloric or isolated pyloric pressure waves between the two postures. We conclude that the effects of gravity on gastric emptying of nonnutrient liquids are likely to reflect changes in both antropyloric motility and intragastric distribution.