bluuebunny/crossref_metadata_2025 huggingface dataset:
Na+-H+ exchange in rat colonic brush-border membrane vesicles
Authors: Foster E. S. , Dudeja P. K. , Brasitus T. A.
Published: December 2017

To demonstrate the presence of a Na+-H+ exchange process in brush-border membrane vesicles from rat colonocytes, the fluorescence response of acridine orange was used to monitor the formation and dissipation of pH gradients. An inwardly directed Na+ gradient stimulated the outward flux of H+, whereas proton influx was stimulated by an outwardly directed Na+ gradient. Since the ionophore valinomycin in the presence of a K+ gradient did not alter Na+-stimulated proton efflux, the interrelationship of Na+ and H+ movement could not be explained solely on the basis of a membrane potential. Na+-stimulated proton efflux was saturable with a Km for Na+ of 20.1 +/- 1.6 mM. Inwardly directed Li+ gradients also stimulated proton efflux, and the Km for Li+ was 30.2 +/- 1.7 mM. In contrast, impermeant cations failed to stimulate the outward flux of H+. Amiloride (1 mM) inhibited both Na+-stimulated proton efflux and influx. Therefore, Na+-H+ exchange is present in rat colonic brush-border membranes and has characteristics similar to other Na+-H+ antiporters. This exchange process may be an important mechanism for Na+ absorption in the large intestine.
Cholecystokinin, carbachol, gastrin, histamine, and forskolin increase [Ca2+]i in gastric glands
Authors: Chew C. S.
Published: December 2017

The Ca2+-selective fluorescent probe quin 2 was used to measure changes in the concentration of free cytosolic [Ca2+] in isolated rabbit gastric glands. Both carbachol and cholecystokinin octapeptide (CCK-8) were found to increase transiently intracellular Ca2+ concentration, [( Ca2+]i) with maximal increases from approximately 0.15 to 0.5 microM occurring within 4–6 s following secretagogue addition. Increases in [Ca2+]i were dose dependent and inhibited by appropriate antagonists. Prestimulation with either carbachol or CCK-8 effectively prevented increases in [Ca2+]i in response to the other agonist. Acute removal of extracellular Ca2+ slightly reduced the increase in [Ca2+]i that occurred following secretagogue addition but had no effect on pepsinogen secretion. Severe Ca2+ depletion resulted in potent inhibition of the quin 2 signal and suppressed basal pepsinogen release and reduced, but did not totally block, pepsinogen release in response to carbachol and CCK-8. Gastrin stimulation also elevated [Ca2+]i in glands, but this agonist was only 40–50% as effective as CCK-8. The cAMP-dependent agonists histamine and forskolin increased [Ca2+]i to approximately the same degree as gastrin. There was a definite lag in the rise in [Ca2+]i following simulation with histamine and forskolin compared with carbachol and CCK-8, which suggests that additional biochemical events occur between agonist-receptor binding and the rise in [Ca2+]i observed with the cAMP-dependent agonists. Both cAMP-dependent and -independent agonists induced an increase in autofluorescence that was slower than the rise in [Ca2+]i but equally affected by extracellular Ca2+ depletion.
Morphine initiates migrating myoelectric complexes by acting on peripheral opioid receptors
Authors: Telford G. L. , Hoshmonai M. , Moses A. J. , Szurszewski J. H.
Published: December 2017

Page G557 and contents: G. L. Telford, M. Hoshmonai, A. J. Moses, and J. H. Szurszewski. “;Morphine initiates migrating myoelectric complexes by acting on peripheral opioid receptors.” Dr. Moshe Hashmonai's last name was spelled incorrectly as Hoshmonai.
Calcium-activated potassium channels and fluid secretion by exocrine glands
Authors: Petersen O. H.
Published: December 2017

Fluid secretion by exocrine glands is regulated by neurotransmitters and hormones. The secretagogues act on the acinar cells by switching on two types of conductance pathways: K+-selective channels in the basolateral membrane and Cl(-)-selective channels localized to the luminal membrane. The K+ channels have been quantitatively characterized in patch-clamp single-channel and whole-cell current-recording studies. Opening of the K+ channels is determined by the membrane potential (depolarization enhances the probability of channel opening), and the intracellular free Ca2+ concentration ([Ca2+]i) (a rise in [Ca2+]i increases the open-state probability). The Cl- channels are also controlled by internal Ca2+ in such a way that an elevation of [Ca2+]i favors opening. Secretagogues evoking an increase in [Ca2+]i activate both sets of channels causing a substantial loss of cellular KCl. KCl is taken up via a Na+-K+-2Cl- cotransport mechanism in the basolateral membrane and the Na+ uptake activates the Na+-K+ pump. In the steady-state stimulated situation the three basolateral transport proteins, the K+ channels, the Na+-K+ pump, and the Na+-K+-2Cl- cotransporter operate together as an electrogenic Cl- pump. Cl- exits into the lumen via the Ca2+-activated Cl- channels and Na+ follows through the paracellular shunt pathway. When stimulation of the acinar cells ceases the K+ and Cl- conductance pathways close and the Na+-K+ pump together with the Na+-K+-2Cl- cotransporter operate as a KCl pump, restoring the intracellular KCl lost initially after start of stimulation and secretion stops.
Postprandial hemodynamics in the conscious rat
Authors: Anzueto Hernandez L. , Kvietys P. R. , Granger D. N.
Published: December 2017

The postprandial intestinal hyperemia was studied in conscious and anesthetized rats using the radioactive microsphere technique. Carbohydrate, protein, lipid, and mixed meals, and the vehicle (Tyrode's solution), were placed in the stomach via a gastrostomy tube. In conscious rats, blood flow increased by 40-80% in the duodenum and jejunum 1 h after either a carbohydrate, lipid, protein, or mixed meal. Tyrode's solution produced a comparable hyperemia. Blood flow in the distal bowel segments (ileum, cecum, and colon) was significantly increased only by Tyrode'ds solution and the carbohydrate meal. The proximal intestinal hyperemia produced by the mixed meal in conscious animals was significantly attenuated by vagotomy yet unaltered by atropine pretreatment. In contrast to the results obtained from conscious rats, the mixed meal did not significantly alter intestinal blood flow in anesthetized animals. The results of this study indicate that the postprandial intestinal hyperemia is much greater in conscious than anesthetized animals. This difference may result from the higher resting blood flows in the latter group. The hyperemic response in conscious animals may be mediated by the vagus nerve.
Ion transport in rat proximal colon in vivo
Authors: Lubcke R. , Haag K. , Berger E. , Knauf H. , Gerok W.
Published: December 2017

Active Na+ absorption by the rat proximal colon in vivo is for the most part electrically silent. The rheogenic Na+ flux makes up only 8%. To elucidate the underlying transport pathways, the following experimental approaches were used: ion substitution experiments such as choline for Na+, cyclamate for Cl-, variation of luminal pH; administration of known inhibitors; and determination of changes in luminal CO2 tension and pH. The transcolonic ion fluxes as well as the electrical parameters potential difference, specific electrical resistance, and short-circuit current were monitored. Na+ transport was drastically reduced in the absence of luminal Cl-, and vice versa Cl- absorption was blocked at zero Na+. NaCl absorption was blocked by amiloride (10(-3) M) and 4-acetamido-4'-isothiocyanostilbene-2, 2'-disulfonic acid and was lowered by acetazolamide. Colonic NaCl absorption was not influenced by luminal furosemide. Na+ absorption increased with alkalinization of the luminal fluid. Tris instead of HCO-3 buffer at constant pH favored Cl- uptake. The results may easily be explained by the operation of a Na+-H+ antiport functionally coupled to a Cl(-)-HCO-3 antiport. These transport processes are supposed to be present in the columnar cells of the colonic epithelium. There is good evidence for the association of K+ secretion with rheogenic Cl- secretion by the crypt cells.
Colonic peristaltic reflex: identification of vasoactive intestinal peptide as mediator of descending relaxation
Authors: Grider J. R. , Makhlouf G. M.
Published: December 2017

Isolated segments of rat and guinea pig midcolon were used to examine the neurotransmitters responsible for ascending contraction and descending relaxation components of the peristaltic reflex. Graded radial stretch of the extreme orad end caused only descending relaxation accompanied by significant release of vasoactive intestinal peptide (VIP) in rat (82%, P less than 0.005) and guinea pig (47%, P less than 0.05). Radial stretch of the caudad end caused only ascending contraction without VIP release. VIP antiserum (1:480 to 1:60) inhibited descending relaxation in a concentration-dependent manner at all grades of stretch (40 +/- 12% to 74 +/- 15%) but augmented ascending contraction (25 +/- 7% to 108 +/- 21%). Axonal blockade with tetrodotoxin and ganglionic blockade with hexamethonium abolished both components, indicating the participation of cholinergic neurons. Atropine and the tachykinin antagonist [D-Pro2,D-Trp7,9]substance P inhibited ascending contraction but not descending relaxation; their combination abolished ascending contraction at all grades of stretch. We conclude that cholinergic neurons coupled to VIP motor neurons regulate descending relaxation and that cholinergic neurons coupled to tachykinin and cholinergic motor neurons regulate ascending contraction.
Differences in pancreatic enzyme release from ventral and dorsal areas of the rat pancreas
Authors: Bruzzone R. , Trimble E. R. , Gjinovci A. , Renold A. E.
Published: December 2017

The exocrine secretory function of the ventral and dorsal areas of the rat pancreas was investigated separately. In the isolated perfused rat pancreas, caerulein (10(-12), 10(-11), and 10(-10) M) and carbachol (10(-7) and 10(-6) M) caused a greaterfold increase in pancreatic secretion from the dorsal than the ventral area. Caerulein (10(-9) M) and carbachol (10(-5) M) were supramaximal concentrations with respect to secretion from the dorsal area, but this was not the case in the ventral area. Similar findings were also observed when ventral and dorsal secretions were studied in vivo in anesthetized animals. By contrast, in dispersed acini the sensitivity and responsiveness of tissue from the dorsal and ventral areas were similar to both secretagogues. The possible influence of the endocrine pancreas via the insuloacinar portal system was studied in the perfused pancreas of diabetic rats treated with insulin in vivo. Carbachol (10(-6) M)-stimulated secretion from the ventral area was similar (except for amylase) to that of controls, while a significantly reduced (P less than 0.001) output was measured from the dorsal pancreas. These results demonstrate that in the intact pancreas differences of exocrine secretion exist between the ventral and dorsal areas and suggest that insulin may contribute, at least in part, to the expression of such differences.
Regulation of muscarinic acetylcholine receptors in cultured guinea pig pancreatic acini
Authors: Hootman S. R. , Brown M. E. , Williams J. A. , Logsdon C. D.
Published: December 2017

Regulation of muscarinic receptors in cultured guinea pig pancreatic acini was investigated by assessing the effects of cholinergic agonists on binding of [N-methyl-3H]scopolamine [( 3H]NMS) and on amylase release. Freshly dispersed acini bound [3H]NMS with a Kd of 74 pM and a maximal binding level (Bmax) of 908 fmol/mg DNA. Carbachol (CCh) stimulated amylase secretion and inhibited [3H]NMS binding. Incubation of acini for 30 min with 0.1 mM CCh decreased the subsequent efficacy of CCh in stimulating amylase release by threefold but had no effect on its potency. In contrast, amylase release in response to cholecystokinin octapeptide (CCK-8) was not altered by CCh preincubation. [3H]NMS binding to acini was decreased only 15–20% after 30-min incubation with CCh. However, culture of acini with 0.1 mM CCh decreased [3H]NMS binding by 50% at 3–4 h and by 85–90% at 24 h. This decrease was attributable primarily to a reduction in Bmax. [3H]NMS binding also was decreased to a similar extent by the cholinergic agonists bethanechol and methacholine but not by other secretagogues. The decrease in antagonist binding induced by CCh was dose dependent, with the IC50, 5.8 microM, approximating the EC50 for amylase release, 4.3 microM. Culture of acini for 24 h with CCh abolished subsequent amylase release in response to CCh but not to CCK-8. When CCh was removed from the culture medium after 24 h and acini recultured in its absence, [3H]NMS binding increased with a half-time for recovery of 20–24 h; this recovery was blocked by cycloheximide.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of duodenal Ca2+ pump by calmodulin and vitamin D-dependent Ca2+-binding protein
Authors: Ghijsen W. E. , Van Os C. H. , Heizmann C. W. , Murer H.
Published: December 2017

The Ca2+ pump in rat duodenal epithelium is studied as ATP-dependent Ca2+ uptake in a vesicle preparation with a 9-fold purification in Na+-K+-ATPase activity and a 20-fold purification of Na+-K+-ATPase with respect to an endoplasmic reticulum marker. ATP-dependent Ca2+ uptake is reduced by 60% by digitonin treatment of the vesicles, whereas high-affinity Ca2+-ATPase is stimulated by the same treatment. Different methods to deplete membrane preparations of calmodulin have been used. In EDTA osmotically shocked vesicles, calmodulin stimulated ATP-dependent Ca2+ transport up to 100% in a Ca2+ concentration-dependent manner. The duodenal Ca2+ pump is inhibited by calmodulin antagonists only at low Ca2+ concentrations and in membranes not depleted from calmodulin. Vitamin D-dependent Ca2+-binding protein (Mr = 10,000) in concentrations up to 5 microM did not affect the rate of ATP-dependent Ca2+ transport, either in Ca2+-EGTA-buffered solutions or in EGTA-free solutions. In membrane preparations from vitamin D-deficient rats, the effects of calmodulin and of Ca2+-binding protein were identical to the vitamin D-repleted control preparations. This excludes a specific effect of Ca2+-binding protein and calmodulin in the vitamin D dependency of duodenal Ca2+-ATPase.
Sodium and chloride transport in the large intestine of potassium-loaded rats
Authors: Budinger M. E. , Foster E. S. , Hayslett J. P. , Binder H. J.
Published: December 2017

Increased dietary potassium ("potassium loading") induces several adaptive changes in colonic function, including increased potential-dependent potassium secretion, active potassium secretion, and Na-K-ATPase activity, but does not alter net sodium absorption in vivo. To establish whether potassium loading stimulates active sodium transport, unidirectional, net sodium, and chloride fluxes were determined under voltage-clamp conditions across isolated rat distal colonic mucosa. In normal animals net sodium flux (JNanet), net chloride flux (JClnet) and short-circuit current (Isc) were 6.1 +/- 1.1, 8.4 +/- 1.0, and 0.7 +/- 0.1 mu eq X h-1. cm-2, respectively; potassium loading significantly increased JNanet and Isc by 4.9 +/- 1.4 and 3.5 +/- 0.7 mu eq X h-1 X cm-2, respectively, without changing JClnet. Amiloride (0.1 mM) inhibited the increases in JNanet and Isc produced by potassium loading. In Cl-free Ringer solution in normal animals JNanet was reduced to 0.6 +/- 0.3 mu eq X h-1 X cm-2. Potassium loading produced identical increases in JNanet and Isc, which were also completely inhibited by 0.1 mM amiloride. These studies establish that potassium loading induces amiloride-sensitive electrogenic sodium absorption without affecting electroneutral sodium-chloride absorption.
Mast cells in the regulation of intestinal electrolyte transport
Authors: Russell D. A.
Published: December 2017

Experiments were performed to determine the ionic basis and physiological messengers of transepithelial ion transport alterations (short-circuit current, Isc) measured during the induction of intestinal anaphylaxis in an Ussing chamber. Antigens derived from Trichinella spiralis, an intestinal parasite, were used to challenge jejunal tissue from guinea pigs immunized by infection with the parasite. Histamine (10(-4) M) caused an increased in Isc that was similar to that induced by antigen. Diphenhydramine (10(-5) M) inhibited the epithelial electrical responses to histamine by 100% and to antigen by 60-70%. Indomethacin (10(-5) M), in combination with diphenhydramine, completely inhibited the antigen-induced rise in Isc. Furosemide (10(-4) M) caused 50-60% inhibition of the increase in Isc induced by antigen and histamine. Antigen challenge of isolated enterocytes did not alter intracellular cAMP content. However, antigen challenge of jejunal segments in which epithelial cells were in contact with sensitized mast cells increased mucosal cAMP content. These results suggest that electrogenic Cl- secretion, mediated in part by cAMP, contributes to antigen-induced jejunal ion transport changes and that histamine and prostaglandins are involved in eliciting these epithelial responses.
Ornithine decarboxylase and mucosal growth in response to feeding
Authors: Tabata K. , Johnson L. R.
Published: December 2017

The purpose of this study was to examine the role of ornithine decarboxylase (ODC) in the stimulation of the growth of gastrointestinal mucosa following feeding. Rats were divided into five groups: 1) fasted for 2 days, 2) fasted for 2 days and refed for 2 days, 3) fasted for 2 days and refed with the addition of 5% difluoromethylornithine (DFMO) to the drinking water, 4) normally fed, and 5) normally fed plus 5% DFMO in the drinking water. In general the results show a significant dissociation between ODC activity and growth of gastrointestinal mucosa in response to feeding. In the gastric mucosa, growth was inhibited by fasting and DFMO and stimulated by feeding, but there were no significant changes in ODC activity in any of the five groups. In the ileum ODC activity increased dramatically in refed rats and was essentially eliminated in rats fed DFMO. DFMO, however, had no effect on mucosal growth in fed rats and only prevented part of the trophic response to refeeding. The results in the colon were much the same as in the ileum, except that DFMO prevented even less of the trophic response to refeeding, despite total inhibition of ODC. These data suggest that polyamines necessary for growth of gastrointestinal mucosa following feeding are not supplied by the rapid activation of mucosal ornithine decarboxylase.
Vasoactive intestinal peptide may participate in the vasodilation of the dog hepatic artery
Authors: Varga G. , Kiss J. Z. , Papp M. , Vizi E. S.
Published: December 2017

The possible direct action of vasoactive intestinal peptide (VIP) on dog hepatic arterial wall or on the noradrenergic innervation of the artery was investigated in vitro. In addition, VIP-containing nerve fibers and terminals were located in the wall of the artery with immunochemical staining. Direct evidence showed that VIP did not affect the release of [3H]norepinephrine but reduced the response of the isolated hepatic artery to electrical field stimulation and exogenous norepinephrine. This suggests that the effect of VIP is postjunctional on the smooth muscle of the artery. VIP-containing nerve fibers and varicosities were observed in the adventitial and medial layer of the arterial wall. These findings strongly support the hypothesis that vasoactive intestinal peptide is a physiological mediator of vasodilation in the hepatic artery.
Production and secretion of intrinsic factor by isolated rabbit gastric mucosa
Authors: Serfilippi D. , Donaldson R. M.
Published: December 2017

During 24 h of organ culture, rabbit gastric fundic mucosal explants maintain constant tissue levels of intrinsic factor (IF) while steadily secreting this glycoprotein into culture medium. Mucosal explants thus generate in one day an average of 1.8 pmol of new IF per milligram mucosal protein, an amount corresponding to 70% of IF present in explant tissue. Cultured explants also incorporate [35S]methionine into tissue IF and secreted IF at a constant rate. Histamine combined with isobutylmethylxanthine stimulates explants to release IF into the culture medium, but tissue levels of IF are diminished and specific activities of tissue and secreted IF remain the same. Fluorograms of 35S-labeled proteins generated by cultured explants fail to show cobalamin-binding precursors or breakdown products of IF. These findings complement previous morphological documentation of IF synthesis by gastric mucosa. Histamine appears to stimulate IF secretion without altering IF synthesis.
Lymph pressure in rat intestinal lymph duct with lymphatic obstruction
Authors: Lee J. S.
Published: December 2017

Lymph pressure (PL) in the main intestinal lymph duct with obstruction of lymph flow was determined. Under various conditions, the rate of lymph flow (JL) was essentially the same in either A rats (with communications between hepatic and intestinal lymphatics) or B rats (without such communications), but PL of A rats was significantly lower (P less than 0.01) than that of B rats. When the intestine was in the basal state, JL of A and B rats was 0.2-0.3 ml/h per rat, and PL was 1.5 +/- 0.2 and 3.3 +/- 0.2 mm/Hg, respectively. During fluid absorption, JL of A and B rats increased to 0.8-0.9 ml/h, and PL was 2.1 +/- 0.4 and 6.4 +/- 0.7 mmHg, respectively. During intravenous saline infusion, JL of A and B rats increased greatly to approximately 14 ml/h, and PL was 3.1 +/- 0.3 and 10.4 +/- 1.1 mmHg, respectively. The lower PL in A rats is apparently due to the possibility that during lymphatic obstruction most lymph could be drained off by the hepatic lymphatics. In A rats, luminal distension pressure had no effect on PL but in B rats PL decreased when distension pressure was 20 mmHg or higher. Furthermore, lymph pressure waves indicate the occurrence of rhythmical contractions of the lymph duct or its surrounding tissues, which may play a role in the propulsion of lymph.
Effect of trimebutine on intestinal motility and plasma motilin in the dog
Authors: Poitras P. , Honde C. , Havrankova J. , Lahaie R. G. , Trudel L. , Goyer R. , Junien J. L. , Pascaud X.
Published: December 2017

In a previous report, trimebutine was shown to induce premature periods of phase III activity in fasting dogs, and its action was blocked by naloxone. In this study, we observed that trimebutine (5 mg X kg-1 iv) could induce premature phase IIIs in canine small intestine during interdigestive and digestive periods; trimebutine-induced phase IIIs were migrating along the small intestine faster than spontaneous activity fronts and; trimebutine-induced phase IIIs were accompanied by sharp rises in concentrations of plasma motilin. To further elucidate the trimebutine-stimulatory mechanism, we verified its effects on the release of various circulating peptides that influence intestinal motility: short-interval blood sampling during trimebutine infusion revealed that plasma motilin increases induced by trimebutine preceded the beginning of phase III in proximal duodenum; and gastrin and insulin postprandial releases were abolished by trimebutine. Therefore, trimebutine, by its simultaneous but opposite effects on various peptides that individually carry positive (e.g., motilin) or negative (e.g., gastrin and insulin) influences on the generation of activity fronts, could alter the equilibrium between stimulatory and inhibitory forces in such a way that, in some circumstances (e.g., postprandial period), stimulatory mechanisms become predominant.
Sodium-proton exchange in colon brush-border membranes
Authors: Binder H. J. , Stange G. , Murer H. , Stieger B. , Hauri H. P.
Published: December 2017

Apical membrane vesicles were prepared from proximal and distal segments of the large intestine of the rat by a method based on morphological criteria and were used to determine 22Na uptake. In both preparations an outwardly directed proton gradient stimulated 22Na uptake. In proximal colon a decrease in vesicular volume induced by an increased media osmolarity led to diminished 22Na uptake at 90 min; a significant (50-60%) portion of uptake represented binding. Initial uptake was linear for 10 s and extrapolated through zero, indicating minimal extravesicular binding. Initial uptake was a saturable function of medium Na concentration. In both preparations initial influx of 0.1 mM NaCl was inhibited by amiloride (0.1-1.0 mM), 15 mM NaCl, 15 mM LiCl, and 15 mM NH4Cl. From the characteristics of the initial 22Na influx we conclude that the apical membrane from colonocytes of proximal and distal segments contains a Na-H exchange with properties similar to those described in other epithelia.
Adrenergic agents stimulate and cholinergic agents inhibit H+ secretion by amphibian jejunum
Authors: White J. F. , Britanisky R.
Published: December 2017

In vitro segments of Amphiuma jejunum secrete H+ spontaneously. This study explored the effect of cholinergic and adrenergic agents on H+ secretion. Segments of mucosa were short-circuited and exposed on their mucosal surface to HCO3- -buffered medium while the pH of the unbuffered serosal medium was held by the pH-stat technique. Methacholine added to the serosal medium nearly abolished the spontaneous short-circuit current (Isc) and serosal alkalinization (JHCO3-) with an EC50 of 3.7 X 10(-7) M. Subsequent addition of norepinephrine (NE) to the serosal medium caused a dose-dependent increase in Isc and JHCO3. For three catecholamines the order of potency was epinephrine greater than NE greater than isoproterenol. The spontaneous Isc was significantly reduced (P less than 0.05) by the gastric H+-K+-ATPase inhibitor omeprazole, while the NE-induced Isc was unaltered by the inhibitor. Replacement of medium Na+ with choline abolished the response to NE. The NE-induced Isc was also reduced by methacholine. Acetazolamide inhibited the spontaneous and NE-induced Isc and JHCO3. In summary, cholinergic and adrenergic agents have opposing effects on intestinal H+-HCO3- transport. Jejunal acid secretion may be controlled in part by these antagonistic influences. Adrenergically activated acid secretion occurs by a different mechanism than spontaneous acid secretion.
Characteristics of rat pancreatic zymogen granules prepared by different methods
Authors: Niederau C. , Grendell J. H. , Rothman S. S.
Published: December 2017

Zymogen granules isolated from tissue homogenates by differential centrifugation in isotonic sucrose solutions show substantial release of digestive enzyme when suspended in isotonic NaCl and in sucrose solutions at pH values above neutrality. A recent study reported a new method for isolating granules, involving the use of a complex homogenization medium and a Percoll gradient that was claimed to produce "stable" granules, i.e., granules that do not release their content in salt solutions and at pH values at or above neutrality. In the present study, we compare granules prepared in both ways, particularly in terms of their tendency to release amylase in isotonic ionic solutions and as a function of pH. The relative absence of amylase release from granules isolated by the new technique was found to be attributable to simple differences in the details of the experimental procedures that were used and not to actual differences in the characteristics of the two granule preparations. For example, previous studies with granules prepared in sucrose solutions reported substantial salt-induced release at 37 degrees C, whereas the recent study reporting the absence of salt-induced release from granules obtained from a Percoll gradient was done at 24 degrees C. Under the identical experimental conditions as used in the present study, little amylase release was seen at 24 degrees C for granules isolated by either technique, but substantial release was seen for both at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
Fate of pancreatic enzymes during small intestinal aboral transit in humans
Authors: Layer P. , Go V. L. , DiMagno E. P.
Published: December 2017

To determine survival of pancreatic enzymes during small intestinal aboral transit in humans, seven healthy volunteers were intubated with an oroileal tube. By using nonabsorbable markers we measured the cumulative amount of lipase, trypsin, and amylase activities and lipase and trypsin immunoreactivities delivered postprandially to the duodenum, midjejunum, and terminal ileum. We found that as the enzymes moved from duodenum to ileum, 74% of amylase activity, 22% of trypsin activity, and 1% of lipase activity survived transit. Enzymatic activity and immunoreactivity of trypsin and lipase disappeared at different rates, suggesting that for these enzymes the sites of enzymatic activity and immunorecognition are not identical. Since tryptic activity is present even in the absence of immunorecognizable trypsin, complete structural integrity of the trypsin molecule may not be essential for its enzymatic activity. The short intraluminal survival of lipolytic activity may partially explain why patients with progressive exocrine pancreatic insufficiency malabsorb fat earlier than other nutrients.
Differences in uptake and esterification of saturated analogues of cholesterol by rat small intestine
Authors: Bhattacharyya A. K.
Published: December 2017

Coprostanol and cholestanol are two saturated analogues of cholesterol. The former, which is the A/B ring isomer of cholesterol, is a nonabsorbable sterol, whereas the latter, which has an A/B ring configuration closer to that of cholesterol, is absorbed only half as efficiently as cholesterol. Intestinal mucosal cell uptake and esterification, two important steps in absorption, were studied in vivo after feeding the sterols and in vitro using everted sacs of rat small intestine. The results showed that the intestinal tissue content of coprostanol, total and esterified, were significantly lower than that of cholestanol. Total cholesterol concentration in the intestinal tissue was similar throughout but the esterified cholesterol content increased significantly throughout the length of the intestine compared with controls. The study suggests that cholestanol is absorbable because its uptake and esterification are not limited, whereas coprostanol is nonabsorbable because its uptake and esterification are limited in the intestinal mucosa. Also, the two sterols stimulate the activities of cholesterol esterase, one of the cholesterol esterifying enzymes, in the intestinal mucosa. The present study along with previous studies suggests that the structure of the sterol molecule as a whole appears to be the important determinant for its uptake and esterification, and probably absorption, in the small intestine.
Uptake pathways for amino acids in mouse intestine
Authors: Karasov W. , Solberg D. , Carter S. , Hughes M. , Phan D. , Zollman F. , Diamond J.
Published: December 2017

This paper characterizes amino acid (AA) uptake pathways in an everted-sleeve preparation of mouse jejunum. AA uptake is linear with time for 2-4 min, depending on the particular AA and its uptake rate. Escape of tracer to the serosal surface is still negligible at these times. Errors due to metabolism of labeled AAs to volatile products can be minimized by using 14C- rather than 3H-labeled AAs and by not drying tissues before counting. The dependence of AA uptake on concentration shows saturable kinetics, with apparent Km values in the range 1-4 mM. By 25 or 50 mM an uptake plateau is reached for leucine, lysine, methionine, and methylaminoisobutyric acid but not for aspartic acid, histidine, or proline. Proline kinetics are the result of a saturable Na+-dependent component, a linear diffusional component, and possibly a small saturable Na+-independent component. The Na+-dependent component of uptake for six AAs averages 83% of the total at 0.01 mM and 54% at 25 or 50 mM. Leucine and D-glucose exhibit modest (32%) cross-inhibition of Na+-dependent uptake. For the same six AAs we determined the percent inhibition of both the Na+-dependent and the Na+-independent components by the other AAs. These results suggest the presence of at least five or six AA uptake pathways in mouse jejunum: distinct Na+-dependent pathways for acidic, basic, and neutral AAs and for imino acids; a shared Na+-independent pathway for basic and neutral AAs; and possibly a Na+-independent pathway for acidic AAs. Comparisons of AA uptake pathways in mouse, rabbit, and rat intestine reveal many similarities but also some differences.
Structural and functional changes by ethanol on in vitro guinea pig gastric mucosa
Authors: Rutten M. J. , Ito S.
Published: December 2017

Relationships between morphological and electrophysiological changes with low concentrations of ethanol on in vitro guinea pig gastric mucosa were investigated. Tissues mounted in Ussing chambers allowed recording of transepithelial potential difference (PD), resistance (R), short-circuit current (Isc), and acid secretion (H+). At selected times the mucosae were processed for morphological analysis. With luminal 10% ethanol there was a decrease in PD, R, Isc, and H+ within 1 min, and they eventually went to low steady-state values between 10 and 40 min. At 1 min many surface epithelial cells lifted off from the basal lamina but were still anchored by thin basal cell processes. After 10 min in ethanol many surface cells had completely detached from the basal lamina but remained connected to adjacent cells by their junctions. Numerous cytoplasmic blebs formed on both apical and basal cell surfaces. Concurrently, there was a significant increase in microvillus length. After 40 min most of the surface cells were detached from the basal lamina as sheets forming epithelial blisters. Upon ethanol washout there was epithelial cell reattachment to the basal lamina and a return of the PD, R, and Isc to control values within 40 min. Incubation of the luminal surface with 10% ethanol for 5 h resulted in a gradual rise of the PD, R, Isc, and H+ to control values by 4 h with a coincident return of the normal mucosal morphology. These studies indicate that ethanol has reversible and possibly adaptable effects on the in vitro guinea pig gastric mucosa and that the morphological changes are closely correlated with the decline and recovery of the electrical and secretory activity of the tissue.
Dissociation of contraction and muscarinic receptor binding to isolated smooth muscle cells
Authors: Collins S. M. , Crankshaw D. J.
Published: December 2017

We examined changes in [3H]QNB binding and cell length induced by muscarinic ligands in a suspension of single smooth muscle cells isolated from the canine stomach. Cells contracted following a brief (30 s) exposure to picomolar concentrations of muscarinic agonists and yielded ED50 values of 1.0 +/- 0.7 pM for oxotremorine, 12.5 +/- 1.8 pM for carbachol, and 16.0 +/- 2.9 pM for metacholine. Contraction was inhibited by atropine with a pA2 value of 10.2 +/- 1.1. The binding of [3H]QNB was rapid and reversible and was stereospecific and pharmacologically appropriate. Specific binding of [3H]QNB was saturable and bound with high affinity (KD 1.04 +/- 0.23 nM) to a single class of sites, of which there were approximately 200,000/cell. In competition experiments antagonist binding was generally homogeneous, whereas that of agonists was heterogeneous and subpopulations of binding sites with different affinities for agonists were identified. The Ki value of 8.1 +/- 1.1 nM for inhibition of QNB binding by atropine was greater than the pA2 of 10.2 +/- 1.1 derived from contraction studies. Furthermore, whereas picomolar concentrations of agonists induced cell contraction, substantially higher concentrations (10 nM to 10 mM) were required to inhibit [3H]QNB binding to the isolated cells.
Response of isolated rat jejunum to angiotensin peptides
Authors: Levens N. R.
Published: December 2017

Following intravenous infusion, angiotensin I (ANG I), angiotensin II (ANG II), and angiotensin III (ANG III) enhance Na and water absorption across the jejunum by increasing sympathetic nerve activity. Increased absorption following intravenous infusion of angiotensin peptides may be secondary to an increase in ion transport. To test this hypothesis, the effect of angiotensin peptides on ion and water absorption from the isolated jejunum was studied. At a dose of 100 pM, serosal addition of ANG II stimulated jejunal Na and water absorption. In contrast, mucosal additions of the peptide were ineffective at doses up to 1 microM. ANG II enhanced jejunal absorption in the presence of prazosin. Thus ANG II does not appear to stimulate absorption from the isolated intestine through mediation of sympathetic fibers. ANG III and the substituted analogue [Sar1,Leu8]ANG II stimulated jejunal absorption at a dose of 100 pM. At a dose of 1 nM ANG I also stimulated jejunal absorption. The effect of ANG I on absorption could be prevented by prior treatment of the animals with the converting enzyme inhibitor MK 422. Thus ANG I must first be converted to ANG II to stimulate jejunal absorption.
Evidence for reflex adrenergic inhibition of acid secretion in the conscious rat
Authors: Dimaline R. , Carter N. , Barnes S.
Published: December 2017

In conscious gastric fistula rats, gastric distension with saline to a pressure of 7 cm caused a threefold reduction of basal gastric acid secretion. Distension with 6.25% peptone solution to the same pressure doubled basal acid secretion. The saline distension-induced inhibition was abolished by guanethidine and markedly reduced by propranolol; phentolamine was ineffective. The response to peptone was unaffected by guanethidine. The results suggest that in the rat, gastric distension at physiological pressures inhibits acid secretion by a beta-adrenergic reflex. The inhibition can be masked by concurrent chemical stimulation of the gastric mucosa by the digestion products of food.
Dietary potassium modulates active potassium absorption and secretion in rat distal colon
Authors: Foster E. S. , Sandle G. I. , Hayslett J. P. , Binder H. J.
Published: December 2017

To determine the effect of variations in body stores of potassium on the rate of active potassium transport in the large intestine, unidirectional 42K fluxes were performed under short-circuit conditions across isolated distal colonic mucosa of control, dietary potassium-depleted and dietary potassium-loaded rats. Potassium depletion stimulated net potassium absorption (JK net) (0.87 +/- 0.19 vs. 0.49 +/- 0.04 mu eq X h-1 X cm-2, P less than 0.025) due to a 40% increase in mucosal-to-serosal potassium transport (JK m----s). In sodium-free Ringer solution JK net in the potassium-depleted group was also significantly greater than in controls (1.93 +/- 0.26 vs. 1.01 +/- 0.11 mu eq X h-1 X cm-2, P less than 0.005). In contrast, in chloride-free Ringer solution JK net was identical in the control and potassium-depleted groups (0.39 +/- 0.05 vs. 0.46 +/- 0.07 mu eq X h-1 X cm-2, P = NS). Potassium loading reversed net potassium absorption to net potassium secretion (-0.76 +/- 0.08 mu eq X h-1 X cm-2, P less than 0.001) as the result of a decrease in JK m----s and an increase in serosal-to-mucosal potassium transport (JK s----m). Net potassium secretion was abolished in the absence of either sodium or chloride from the bathing solution but not by mucosal amiloride. In sodium-free Ringer solution JK net was similar in control and potassium-loaded groups, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Multispecific anion exchange in basolateral (sinusoidal) rat liver plasma membrane vesicles
Authors: Hugentobler G. , Meier P. J.
Published: December 2017

The mechanisms and driving forces for hepatic uptake of sulfate were investigated in basolateral (sinusoidal) rat liver plasma membrane vesicles. A transmembrane pH difference (pH 8.0 inside, 6.0 outside) stimulated sulfate uptake above equilibrium (“overshoot”). This pH gradient-stimulated sulfate uptake was saturable with increasing concentrations of sulfate and could be inhibited by probenecid, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), carbonyl cyanide p-(trifluoromethoxy)-phenylhydrazone, and nigericin. At low buffer concentrations and pH 6.0 an inwardly directed sodium gradient also stimulated sulfate uptake. This sodium-dependent sulfate uptake could be inhibited by amiloride and DIDS, indicating indirect coupling of sodium and sulfate flux through concomitant sodium-proton and sulfate-hydroxyl exchange. Cisinhibition of initial pH gradient-stimulated sulfate uptake, as well as transstimulation of sulfate uptake under pH-equilibrated conditions (pH 7.5 inside and outside), were observed with sulfate, thiosulfate, oxalate, and succinate, but not with chloride, bicarbonate, acetate, lactate, pyruvate, p-aminohippurate, citrate, glutamate, aspartate, and taurocholate. Furthermore, cholate and sulfobromophthalein exhibited competitive inhibition of pH gradient-stimulated sulfate uptake. In addition, an inside-to-outside hydroxyl gradient also stimulated uptake of cholate and this pH gradient-sensitive portion of cholate uptake was inhibited by extravesicular sulfate. In contrast to basolateral membranes, no evidence for multispecific sulfate-hydroxyl exchange was found in canalicular plasma membrane vesicles.
Effects of medium pH on duodenal and ileal calcium active transport in the rat
Authors: Favus M. J. , Bushinsky D. A. , Coe F. L.
Published: December 2017

To study the effect of pH on Ca active transport in vitro pH was varied from 7.1 to 7.7, and bidirectional transmural Ca fluxes were measured under short-circuited conditions across duodenum or ileum from rats fed either normal chow (NCD, 1.2% Ca) or low Ca (LCD, 0.002% Ca). Duodenum and ileum from rats fed LCD actively absorbed calcium at medium pH 7.4. Reduction in mucosal and serosal medium bicarbonate from 25 to 10 mM (pH 7.4 to 7.1) decreased duodenal net Ca absorption (Jnet) from 121 +/- 32 to 39 +/- 9 nmol X cm-2 X h-1 (P less than 0.02) and ileal Jnet from 74 +/- 13 to 22 +/- 6 (P less than 0.01). The decline in duodenal and ileal Ca Jnet was due to a decrease in the mucosal-to-serosal flux (Jm----s). Raising medium pH from 7.4 to 7.7 by increasing bicarbonate from 25 to 50 mM did not alter Ca Jm----s, serosal-to-mucosal flux (Js----m), or Jnet X Ca fluxes across ileum from rats fed NCD demonstrated net secretion. LCD ileal Jm----s was unaltered when pH was reduced from 7.4 to 7.1 by increasing the PCO2 content of the buffer from 30 to 81 mmHg while maintaining bicarbonate at 24 mM. The results indicate that in vitro conditions that simulate metabolic acidosis (low bicarbonate and pH, normal PCO2) inhibit 1,25D-mediate calcium Jm----s, whereas conditions that simulate respiratory acidosis have no effect on Ca fluxes. The present studies suggest that decreases in calcium Jm----s is by a primary alteration in transport of other ions rather than direct effect on Ca transport.
Gallbladder prostaglandins and lysophospholipids as mediators of mucin secretion during cholelithiasis
Authors: LaMorte W. W. , LaMont J. T. , Hale W. , Booker M. L. , Scott T. E. , Turner B.
Published: December 2017

Mucin hypersecretion from the gallbladder epithelium contributes to cholesterol gallstone formation by accelerating the nucleation of cholesterol-supersaturated bile. Prostaglandins (PGs) and lysophosphatidylcholine (LPC) have both been implicated as potential mediators of mucin hypersecretion, but their roles are unclear. We fed prairie dogs a lithogenic diet (0.34% cholesterol), and after 1, 2, 4, or 6 wk of cholesterol feeding, we measured glycoprotein and LPC concentrations in bile and PG synthesis in gallbladder and liver slices. Hypercholesterolemia and cholesterol supersaturation of bile occurred after 1 wk of cholesterol feeding, but marked crystal formation was delayed until 4 wk, when glycoprotein concentrations became markedly elevated. Glycoprotein hypersecretion was preceded by increased synthesis of PGF2 alpha (P less than 0.002), PGE2 (P less than 0.001), prostacyclin (P less than 0.05), and thromboxane (P = 0.07) in the gallbladder after only 2 wk of cholesterol feeding, but PG synthesis in the liver remained unchanged (P greater than 0.14). LPC concentrations in gallbladder bile also increased at 2 wk (P less than 0.02), but LPC in hepatic bile was unchanged (P = 0.35). In organ culture studies, LPC caused a dose-dependent stimulation of [3H]glycoprotein release from guinea pig gallbladder mucosa that could not be explained solely by LPC's detergent properties. We conclude that gallbladder PG synthesis and LPC production are increased at an early stage of cholesterol gallstone formation in the prairie dog model. These changes probably play a significant role in gallstone pathogenesis, since they mediate hypersecretion of gallbladder mucin and thus favor the nucleation of cholesterol-supersaturated bile.
Suggestion of a role for calmodulin and phosphorylation in regulation of rabbit ileal electrolyte transport: effects of promethazine
Authors: Cohen M. E. , Sharp G. W. , Donowitz M.
Published: December 2017

Suggestion of a role for protein phosphorylation in the regulation of intestinal active NaCl transport was found by studying the effects of low concentrations of promethazine on Ca2+-calmodulin (CaM)-dependent protein phosphorylation of ileal microvillus membranes and on active ileal electrolyte transport. Ca2+-CaM increased the phosphorylation of six microvillus peptides (Mr 137,000, 116,000, 77,000, 58,000, 53,000, and 50,000) in a concentration-dependent manner. Promethazine inhibited the Ca2+-CaM-induced increases in each of these phosphorylations. The effect of promethazine was concentration dependent, with concentrations of 5–12 microM (mean 8 microM) causing 50% inhibition. Promethazine also caused a concentration-dependent increase in net Cl absorption and decrease in the ileal short-circuit current, with 9 microM promethazine causing a change in short-circuit current 50% of maximum. The promethazine effect on microvillus membrane phosphorylation was specific, since neither cAMP- and cGMP-induced phosphorylation in the microvillus membrane nor the stimulation by Ca2+-CaM of myosin light chain kinase phosphorylation of myosin light chain were affected by promethazine. The similar, and unusual sensitivity to low concentrations of promethazine on ileal microvillus membrane phosphorylation increased by Ca2+-CaM and on ileal electrolyte transport is consistent with Ca2+-CaM-dependent microvillus membrane phosphorylation being involved in the regulation of active electrolyte transport in ileal absorptive cells.
The control mechanisms of gastric emptying are not overridden by motor stimulants
Authors: Wulschke S. , Ehrlein H. J. , Tsiamitas C.
Published: December 2017

We wanted to determine if an acceleration of the normal emptying rate by motor stimulants interfers with control mechanisms limiting gastric emptying. Therefore, we studied the effects of 5-hydroxytryptophane (5-HTP) and cisapride on canine gastrointestinal motility and gastric emptying after ingestion of viscous acaloric and nutritive meals. Prolonged contractions and relaxations that change lumen size (isotonic component) and wall tension (isometric component) are defined as “basal contractions” and “basal relaxations”, respectively. The nutrient meal emptied much slower than the acaloric meal due to several alterations of gastric, pyloric, and duodenal motility. Both drugs stimulated antral motility but failed to accelerate gastric emptying of the nutrient meal. The main causes for the failure were a basal relaxation of the proximal antrum and a basal contraction of the duodenum. In conclusion, basal contractions of the proximal antrum and duodenum play an important role in the process of gastric emptying, and under physiological conditions the control mechanisms of gastric emptying provide an optimal emptying rate that cannot be markedly accelerated by 5-HTP and cisapride.