bluuebunny/crossref_metadata_2025 huggingface dataset:
Bovine gallbladder muscularis: source of a myogenic receptor for cholecystokinin
Authors: Schjoldager B. , Shaw M. J. , Powers S. P. , Schmalz P. F. , Szurszewski J. , Miller L. J.
Published: December 2017

Despite being a classic target for the gastrointestinal peptide hormone, cholecystokinin (CCK), the gallbladder CCK receptor is not well characterized. Pharmacological studies of small species suggest that CCK action can be mediated by direct myogenic or by both myogenic and neurogenic receptors. To prepare for the biochemical characterization of a gallbladder CCK receptor and to define the subtype of the receptor being studied, we have performed autoradiographic localization and pharmacological characterization of CCK receptors on bovine gallbladder. Autoradiography demonstrated high-affinity specific CCK-binding sites only on the muscularis. CCK-8 stimulated tonic contraction of longitudinal strips of gallbladder muscularis in a concentration-dependent manner, with an ED50 of 0.2 nM. Antagonism at the cholinergic receptor with 1 microM atropine or axonal transmission with 1 microM tetrodotoxin did not modify CCK-induced contraction, supporting a direct myogenic effect of this hormone. Optimal electrical field stimulation (10 V, 10 Hz, 500 microseconds) to elicit a neuronal response resulted in muscle strip relaxation, which was abolished with adrenergic blockade (1 microM phentolamine, 1 microM propranolol). Although acetylcholine administration stimulated contraction, electrical field stimulation did not, even in the presence of phentolamine, propranolol, and/or CCK. Thus, in bovine gallbladder muscularis, there is evidence for a functional CCK receptor only on smooth muscle cells. Demonstration of a single, high-affinity specific CCK-binding site on an enriched plasma membrane preparation of bovine gallbladder muscularis is consistent with this representing a myogenic CCK receptor.
Reduced mucosal prostaglandin synthesis after massive small bowel resection
Authors: Vanderhoof J. A. , Park J. H. , Grandjean C. J.
Published: December 2017

Exogenous 16,16-di-methyl-prostaglandin (PG) E2 administration augments mucosal hyperplasia after massive small bowel resection in the rat. We, therefore, evaluated the ability of aspirin to inhibit mucosal PG synthesis in the small intestine and further evaluated the effects of reduced PG synthesis on mucosal adaptation after a 70% jejunoileal resection in male Sprague-Dawley rats. Sixteen of 27 resected and 8 of 16 sham-operated rats were given aspirin 20 mg/kg body wt subcutaneously every 8 h for 12 days; the remainder were given vehicle only. Although mucosal PGE2, PGF2 alpha, and thromboxane B2 synthesis were all reduced by aspirin administration to 20-40% of the control values, mucosal adaptation in resected animals as measured by mucosal weight, DNA, protein, and maltase levels was only inhibited in the distal ileum. Aspirin did not affect these values in the duodenum, the upper jejunum, and the midileum. This study provides evidence for some involvement of endogenous PGs in regulation of the mucosal adaptation process in the distal ileum after massive small bowel resection in the rat. However, lack of inhibition more proximally suggests that factors other than PGs are more important.
Conformational change in plasma albumin due to interaction with isolated rat hepatocyte
Authors: Horie T. , Mizuma T. , Kasai S. , Awazu S.
Published: December 2017

The electron spin resonance spectroscopy of 4-isothiocyanato-tempo labeled to bovine serum albumin (BSA) and the absorption spectroscopy of eosin maleimide labeled to BSA in the isolated rat hepatocyte suspension indicate conformational change occurring in the albumin molecule during interaction with the hepatocellular membrane. The conformational change in the albumin molecule may possibly accelerate the dissociation of albumin-organic anion complexes at the surface of the liver cell. The conformational change in the albumin molecule may explain in part the mechanism of albumin-mediated hepatic transport.
Cerebral evoked potentials after endorectal mechanical stimulation in humans
Authors: Collet L. , Meunier P. , Duclaux R. , Chery-Croze S. , Falipou P.
Published: December 2017

Although numerous clinical studies have proved that impaired rectal sensation is a major factor in fecal continence dysfunctions, objective studies in this field are still lacking. To provide information on normal rectal afferents, a study of cerebral potentials evoked by mechanical stimulation of the rectal wall was carried out in 10 healthy volunteers (5 male, 5 female; age, 33–52 yr). The stimulating device consisted of a rectal balloon rhythmically inflated and deflated by means of an animal breathing ventilator. Recordings were obtained 2 cm behind the vertex (C'z, International system 10–20). The responses were averaged from 300 to 800 sweeps. The average was triggered either on inflation ("on effect") or on deflation ("off effect"). Inflation volume and pressure were adjusted to induce a clear but not painful pulsing sensation. Reproducible responses were recorded by both on and off effects. The evoked potentials were polyphasic with a succession of positive and negative waves (peak latencies between 78 and 310 ms). The shape of the response (morphology, latency, and amplitude) was perfectly reproducible in the same subject. With regard to intrasubject reproducibility, variability was displayed: only the early waves (latency less than 100 ms) were perfectly reproducible; late waves exhibited variable latency and morphology. The present findings are the first demonstration of the possibility of recording an evoked potential on the scalp after a mechanical stimulation of the rectum.
Somatostatin inhibition of secretagogue and forskolin-stimulated gastric acid secretion
Authors: Michelangeli F. , Ruiz M. C. , Rodriguez C. L. , Pelacca A.
Published: December 2017

The action of somatostatin (SS) on acid secretion and histamine release was studied in isolated gastric mucosa of toads mounted in Ussing chambers. SS inhibited H+ secretion and histamine release stimulated by cholinergic and gastrinergic secretagogues. Exogenous histamine stimulation of H+ secretion was blocked noncompetitively by SS in a dose-dependent manner. In mucosae maximally stimulated by histamine or forskolin and cimetidine, acetylcholine (ACh) and tetragastrin (TG) induced a direct stimulation of the oxyntopeptic cell not inhibited by SS. Indomethacin, an inhibitor of prostaglandin synthesis, did not prevent SS inhibition of histamine stimulation. Pretreatment with SS abolished forskolin stimulation of H+ secretion. SS induced a small inhibition of the stimulatory effect of N6, 2'-O-dibutyryladenosine 3',5'-cyclic monophosphate. These results suggest that SS inhibits acid secretion stimulated by secretagogues through different mechanisms: 1) inhibition of histamine release by ACh and TG, 2) inhibition of endogenous and exogenous histamine stimulation through a blockade of adenylate cyclase, and 3) an inhibitory effect subsequent to the synthesis of adenosine 3',5'-cyclic monophosphate. The direct activation of the oxyntopeptic cell by ACh and TG does not seem to be affected by somatostatin.
Ca2+ - and cAMP-induced protein phosphorylation in lacrimal gland basolateral membranes
Authors: Dartt D. A. , Mircheff A. K. , Donowitz M. , Sharp G. W.
Published: December 2017

Basolateral plasma membranes play an integral role in coupling of stimulus to secretion of fluid and protein from the lacrimal gland. To determine if basolateral plasma membranes contain Ca2+- or adenosine 3', 5'-cyclic monophosphate (cAMP)-dependent protein kinases, which could phosphorylate specific proteins important for secretion, a purified preparation of basolateral plasma membranes was prepared from rat exorbital lacrimal glands by differential and density gradient centrifugation. Phosphorylation of basolateral plasma membrane proteins was studied in the presence of [gamma-32P]ATP and was analyzed by sodium dodecyl sulfate-poly-acrylamide gel electrophoresis. Increasing the Ca2+ concentration in the presence of calmodulin stimulated phosphorylation of a 52,000-Mr peptide with a maximal increase in phosphorylation obtained at 3 and 66 microM free Ca2+. The phenothiazines trifluoperazine and promethazine inhibited phosphorylation of this 52,000-Mr peptide; 50% inhibition was obtained at 15 and 95 microM, respectively. Increasing the cAMP level from 0 to 10 microM stimulated phosphorylation of another peptide of 91,000 Mr. This effect could be reproduced by guanosine 3', 5'-cyclic monophosphate, but only at 100 microM. The cAMP concentration causing 50% of maximal phosphorylation was 0.3 microM. We conclude that lacrimal gland basolateral plasma membranes contain Ca2+/calmodulin- and cAMP-dependent protein kinases and protein substrates.
An autoradiographic study of regional distribution of gastric mucosal blood flow
Authors: Angerson W. J. , Geraghty J. G. , Carter D. C.
Published: December 2017

Iodo[14C]antipyrine autoradiography was used to measure gastric mucosal blood flow in anesthetized rats and to study regional distribution. Blood flows of 61 +/- 8 ml.100 g-1.min-1 (means +/- SE) in corpus and 84 +/- 9 ml.100 g-1.min-1 in antral mucosa compared well with previously reported measurements by hydrogen clearance. Blood flow in the crests of corpus mucosal folds was significantly higher than in the valleys between folds, indicating that the greater susceptibility of the former areas to acute injury, documented in several studies, is not associated with a perfusion defect in the resting stomach. Corpus mucosal blood flow was also higher in the side walls of the stomach than in the greater curvature region, and in distal than in proximal locations. No systematic regional variations within antral mucosa were demonstrated.
Specific binding of lactoferrin to brush-border membrane: ontogeny and effect of glycan chain
Authors: Davidson L. A. , Lonnerdal B.
Published: December 2017

Bioavailability of iron from human milk is exceptionally high. It has been suggested that lactoferrin, the major iron-binding protein in human milk, may participate in this high iron bioavailability from milk. We examined the interaction of lactoferrin with the intestinal brush-border membrane using the rhesus monkey as a model. Brush-border membrane vesicles were prepared from monkeys of various ages. Binding studies with 59Fe-labeled human and monkey lactoferrin were performed to examine interaction of lactoferrin with the brush-border membrane. Specific saturable binding of lactoferrin was found at all ages studied (fetal, suckling infant, weaned infant, juvenile, and adult). The dissociation constant for lactoferrin-receptor binding was 9 X 10(-6) M. In contrast, no binding of serum transferrin or bovine lactoferrin occurred. Removal of fucose from the lactoferrin glycans resulted in a significant decrease in binding. It was concluded that lactoferrin in milk may function in the process of iron absorption through interaction with a small intestinal receptor and that fucosylated glycans on the carbohydrate chain of lactoferrin are necessary for receptor recognition.
Effect of aging on intestinal absorption of aromatic amino acids in vitro in the rat
Authors: Navab Farhad , Winter Charles G.
Published: December 2017

Whole-thickness everted jejunal rings were used to measure uptake of l-tyrosine (l-Tyr), l-phenylalanine (l-Phe), and l-tryptophan (l-Trp) in 6-, 12-, and 24-mo-old rats. The rate of uptake of all three amino acids (1 mM) was significantly reduced after 20 min of incubation in 24-mo-old compared with 6-mo-old rats. Results of influx (2 min) of 0.5-40.0 mM l-Phe and l-Trp suggested an increased affinity but decreased capacity for the transporter with age; these differences were significant for l-Trp (P < 0.05). Respective values for apparent Kt and Vmax were the following: l-Phe 6-mo-old rats, 5.46 mM and 1.03 μmol·g-1·2 min-1; 24-mo-old rats, 2.54 mM and 0.51 μmol·g-1·2 min-1; l-Trp 6-mo-old rats, 5.09 mM and 0.38 μmol·g-1·2 min-1; 24-mo-old rats, 3.20 mM and 0.25 μmol·g-1·2 min-1. Values for 12-mo-old rats fell in between the other two age groups.

intestinal weight; intestinal length; Fischer rats; kinetics of uptake; Hofstee plot; everted jejunal rings; neurotransmitter precursors

Submitted on June 14,1986

Accepted on November 9,1987
Sources of calcium for contraction of distal circular muscle or taenia coli in the rabbit
Authors: Sevy N. , Snape W. J.
Published: December 2017

Studies were performed on proximal taenia coli and distal circular muscle from the rabbit to determine if the source of Ca2+ required for bethanechol stimulation of contraction was similar after permeabilizing the tissues with saponin. The EC50 for Ca2+ stimulation of contraction was pCa 6.1 +/- 0.1 for both tissues. The peak response occurred at pCa 4.5. The addition of 1 microM calmodulin did not alter the Ca2+ EC50 or the peak response. Caffeine (20 mM) stimulated contraction of both taenia coli and distal circular muscle. The caffeine-stimulated contractile response was threefold greater in the taenia than in the distal circular muscle (P less than 0.05). Perfusion of thin strips of colonic muscle with buffer, containing 10(-7) M Ca2+, reduced the amplitude of bethanechol-stimulated contraction. The perfusion time to reduce the contraction by 50% was greater in the proximal muscle (2.4 +/- 0.1 min) than in the distal muscle (1.1 +/- 0.5 min) (P less than 0.001). These data suggest that 1) the intracellular Ca2+ concentration necessary for contraction is similar in the proximal and distal colon and 2) the intracellular Ca2+ stores appear to be greater in proximal taenia coli compared with distal circular muscle.
Effect of denervation on initiation and coordination of gastroduodenal motility in turkeys
Authors: Chaplin S. B. , Duke G. E.
Published: December 2017

The effect of total extrinsic denervation of the stomach on the rhythmicity and coordination of the gastroduodenal cycle was determined in domestic turkeys. The vagus and two gastric branches of the sympathetic nerve were sectioned at the level of the glandular stomach. Motilities of the glandular stomach, proximal duodenum, and caudal thin muscle of the muscular stomach were monitored via implanted strain gauge transducers for 1 h every other day. Denervation had no significant effect on initiation of contractions or frequency of gastric contractions in fed birds, but fasted birds whose stomachs were extrinsically denervated exhibited significantly slower contractions than controls. In addition, denervation uncoupled the coordination of the duodenal and gastric contractions in the gastroduodenal cycle. Moreover, birds with extrinsically denervated stomachs exhibited a cephalic phase of gastric motility that was significantly delayed in onset compared with controls. These results suggest the existence of both a neural and endocrine component in the avian gastric response to the sight of food. Extrinsic input seems to be an important modulator of gastric motility in birds and is essential for the normal coordination of the gastroduodenal contraction cycle.
Autoradiographic analysis of hepatocytes in mirex-induced adaptive liver growth
Authors: Wilson D. , Yarbrough J. D.
Published: December 2017

The relationships between [3H]thymidine incorporation into hepatocyte nuclei, cell enlargement, and mitotic index were studied in intact (INT) and adrenalectomized (ADX) mirex-dosed rats. In INT mirex-dosed rats the sequence of events included the following: a biphasic response in nuclear labeling of mononuclear hepatocytes with peaks at 48 and 66 h postmirex dose, a peak in mitotic activity 66 h postmirex dose, and a significant increase in binuclear hepatocyte size 48 h postmirex dose. In ADX mirex-dosed rats the sequence of events included the following: a biphasic response in nuclear labeling of mononuclear hepatocytes with peaks at 24 and 48 h postmirex dose, a peak in mitotic activity 60 h postmirex dose, and a marginal increase in binuclear hepatocyte size 48 h postmirex dose. Corticosterone supplements to ADX mirex-dosed rats significantly reduced nuclear labeling of the mononuclear hepatocytes and increased the size of binuclear hepatocytes to that observed in INT mirex-dosed rats. This study demonstrates that adaptive liver growth consists of a hyperplastic response that involves mononuclear hepatocytes and a hypertrophic response that involves binuclear hepatocytes. Both responses appear to be modulated by corticosterone.
Intestinal anaphylaxis: in vivo and in vitro studies of the rat proximal colon
Authors: Forbes D. , Patrick M. , Perdue M. , Buret A. , Gall D. G.
Published: December 2017

The response of the rat proximal colon to an immunoglobulin E (IgE)-mediated hypersensitivity reaction was examined. Rats were sensitized to egg albumin (EA) by intraperitoneal injection, and serum titers of specific anti-EA IgE were measured at 14 days. Sensitized animals had titers of greater than or equal to 1:64, whereas no anti-EA IgE antibodies were detected in controls. Water and electrolyte absorption in the proximal colon, before and during antigen challenge, was measured by in vivo marker perfusion. Antigen challenge resulted in significant inhibition of water, Na+, Cl-, and K+ absorption in vivo. Proximal colonic tissue from sensitized and control animals was studied in Ussing chambers under short-circuited conditions. Antigen challenge of sensitized tissue resulted in significant increases in short-circuit current due to the induction of active Cl- secretion. No such changes were seen in control tissue. The abnormalities induced by antigen challenge in tissue from sensitized animals was blocked by doxantrazole (10(-3) M), a mast cell stabilizer. The findings indicate that IgE-mediated reactions in rat proximal colon to a food protein cause pertubations in water and electrolyte transport secondary to active Cl- secretion and these abnormalities appear to be due to mast cell degranulation.
Na+ and H+ transport in human jejunal brush-border membrane vesicles
Authors: Kleinman J. G. , Harig J. M. , Barry J. A. , Ramaswamy K.
Published: December 2017

We have examined pH gradient-driven Na+ uptake and Na+-driven H+ transport in brush-border membrane vesicles prepared from jejunal tissue obtained from organ donors by measuring the influx of 22Na and the fluorescence quenching of acridine orange (AO). Vesicle preparation by either Ca2+ or Mg2+ precipitation showed no difference in 22Na uptake or AO fluorescence quenching and dissipation. An outward H+ gradient [intravesicular pH (pHi) 5.5; extravesicular pH (pHo) 7.5] induced a Na+ uptake “overshoot” of threefold over equilibrium, whereas the absence of an H+ gradient (at either pH 5.5 or 7.5) did not produce an overshoot. Voltage clamping by Ki+ = Ko+ plus valinomycin reduced the overshoot by 50%. The initial rate of pH-driven Na+ uptake in voltage-clamped vesicles was related to [Nao+] (Km = 29 mM and Vmax = 9.5 nmol.mg protein-1.3 s-1). Amiloride inhibited this uptake in voltage-clamped vesicles (Ki = 99 microM). Dissipation of AO fluorescence quench in vesicles with a preformed internal acid gradient was hastened by Nao+ as well as voltage clamping in the absence of Na+. In vesicles without a pH gradient, internal Na+, as well as a diffusion potential (Ki+ 100; Ko+ 0 plus valinomycin) in the absence of Na+, induced AO quenching. External Na+ and Li+, but not choline, acted to dissipate AO quenching induced by a diffusion potential, and the rate of dissipation was unaffected by the presence of Cl-.Li+ and NH4+, but not Cs+, K+, Rb+, or choline+, inhibited pH gradient-driven 22Na uptake. We conclude that human jejunal brush-border membrane vesicles contain conductive pathways for both Na+ and H+ and an Na+-H+ exchanger.
Agonist-sensitive calcium pool in the pancreatic acinar cell. I. Permeability properties
Authors: Muallem S. , Schoeffield M. S. , Fimmel C. J. , Pandol S. J.
Published: December 2017

45Ca2+ fluxes and free cytosolic Ca2+ [( Ca2+]i) were used to describe the Ca2+ permeability and Ca2+ reloading of the agonist-sensitive pool at rest, during stimulation, and at termination of stimulation. A sequence of stimulation with carbachol, inhibition with atropine (cycling), and restimulation with cholecystokinin octapeptide (CCK-8) was used to follow Ca2+ reloading. Reloading of the pool required extracellular Ca2+ and was measured as an increased rate and extent of 45Ca2+ uptake into the acini. The 45Ca2+ incorporated into cycled acini could be completely released with CCK-8. The dose-response curves for 45Ca uptake and release were identical to those of the hormonally evoked [Ca2+]i increase. The increased 45Ca2+ uptake during reloading was not due to an expansion of any intracellular pool size but reflects the labeling of the pool to isotopic equilibrium in cycled acini. The rate constant of Ca2+ efflux from the pool of resting cells was approximately 0.67 +/- 0.01/h. With stimulation, the Ca2+ permeability of the pool membrane rapidly increased, resulting in Ca2+ release into the cytosol and an increase in [Ca2+]i. With termination of stimulation, the Ca2+ permeability of the pool membrane rapidly decreased while the pool continued to reload with extracellular Ca2+. Labeling of the pool to isotopic equilibrium allowed determination of the amount of Ca2+ released from the pool, which was 2.94 +/- 0.06 nmol/mg protein. This indicates that total Ca2+ concentration in the pool is in the millimolar range.
Changes in pattern of enzyme secretion by rat pancreas during repeated trypsin inhibitor treatment
Authors: Keim V. , Goke B. , Adler G.
Published: December 2017

In conscious rats with cannulated pancreatic ducts, the synthetic trypsin inhibitor camostat (400 mg/kg) was instilled into the stomach once daily on 5 consecutive days. Each camostat administration stimulated the secretion of juice, bicarbonate, and protein. From day 2 to day 5, basal protein secretion measured before the daily instillation of camostat was increased, whereas basal secretion of volume and bicarbonate remained unchanged. The secretory responses to camostat increased up to day 3 of treatment without further change on days 4 and 5. In response to acute camostat instillation, parallel secretion of enzymes was found. Within 1 day, however, a change in the composition of secreted enzymes was observed. After 3 days, the percentage of amylase in pancreatic juice decreased by approximately 50%, whereas the relative amount of proteinases and the specific activity of phospholipase A2 doubled. The alteration of protein patterns in pancreatic juice parallels the effect on enzymes stored in the gland. The results demonstrate that adaptation of enzyme secretion in the exocrine pancreas occurs after a short period of treatment with camostat. Because this compound stimulated protein, volume, and bicarbonate secretion, it is suggested that other factors in addition to cholecystokinin may be involved in this adaptation process.
Sodium-dependent D-glucose transport after proximal small intestinal resection in rat
Authors: Freeman H. J. , Ellis S. T. , Johnston G. A. , Kwan W. C. , Quamme G. A.
Published: December 2017

Massive small intestinal resection results in both structural and functional changes in the residual small bowel. Sodium-dependent D-glucose transport was examined in brush-border membrane vesicles derived from the terminal 20-30 cm of ileal mucosa of male Sprague-Dawley rats, 2 and 6 wk after 66% proximal jejunoileal resection or jejunoileal transection. Kinetic characteristics for sodium-dependent D-glucose transport were investigated with rapid filtration under conditions of a zero-trans, 100 mM cis-NaSCN gradient. Mucosal weight, protein, and DNA content were increased in the residual terminal intestinal segment compared with transected controls, whereas morphometric studies revealed increased villus and crypt heights as well as an increased mitotic index. Mean kinetic transport parameters at 6 wk after proximal small bowel resection revealed two saturable systems in the distal residual ileum: first, a low-affinity, high-capacity system with a Km of 0.19 +/- 0.03 mM and a Vmax of 0.48 +/- 0.04 nmol.mg protein-1.min-1; and second, a high-affinity, low-capacity system with a Km of 0.009 +/- 0.001 mM and a Vmax of 0.105 +/- 0.016 nmol.mg protein-1.min-1. In contrast, negligible sodium-dependent D-glucose transport was detected in the most distal ileum in control animals or animals 2 wk after resection or 2 and 6 wk after transection. Thus adaptational changes including mucosal hyperplasia and the appearance of two sodium-dependent D-glucose brush-border membrane vesicle transport systems occur in the residual distal intestine after massive proximal small bowel resection.
Stimulation of acid formation in permeable gastric glands by valinomycin
Authors: Hersey S. J. , Steiner L.
Published: December 2017

Isolated gastric glands made permeable with digitonin treatment were employed to study the ionic requirements of acid formation. Acid formation was monitored by the accumulation of a novel weak base probe, [14C]benzylamine. ATP-dependent acid formation was found to require K+ in a concentration-dependent manner, with an apparent K0.5 = 7 mM. The anion dependence of acid formation gave a selectivity sequence of Cl = I greater than Br greater than NO3 greater than SO4 = isethionate, with isethionate being approximately 50% as effective as Cl. The dependence of acid formation on [Cl] gave an apparent K0.5 = 6 mM. Addition of the K+ ionophore, valinomycin, to resting glands (cimetidine pretreatment) resulted in a two- to threefold increase in ATP-dependent acid formation. In contrast, stimulated (forskolin pretreated) glands showed a greater accumulation of benzylamine with ATP but significantly less valinomycin stimulation. The valinomycin stimulation required both K+ and Cl- and was inhibited by omeprazole and Sch 28080. The results are interpreted to indicate that major events in the transition from a resting to a stimulated state include changes in both K+ and anion permeability of the secretory membrane of parietal cells.
Sodium-proton exchanger in isolated hepatocytes exhibits a set point
Authors: Stewart D. J.
Published: December 2017

Na+-H+ exchange activity was examined in hepatocytes isolated from rat liver. Activity was measured as amiloride-sensitive fluorescence changes utilizing the pH-sensitive chromophore, bis(carboxy-ethyl)-carboxyfluorescein. Hepatocytes, after being acidified by an NH4Cl prepulse, exhibit amiloride-sensitive and sodium-dependent alkalinization. The rate of cellular pH recovery after acidification varied with the intracellular pH. The rate was highest at approximately pH 6.4 and declined as the pH rose, ceasing measurable activity at approximately pH 7.3. The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, at a concentration of 10(-6) M, shifted the set point for the exchanger to a more alkaline pH by 0.2-0.3 pH units. The above observations indicate that the Na+-H+ exchanger plays an active role in regulating intracellular pH in liver cells and that hormones acting through protein kinase C may modulate that function.
Cl(-)-HCO3- antiport in rat lacrimal gland
Authors: Lambert R. W. , Bradley M. E. , Mircheff A. K.
Published: December 2017

With the use of analytical subcellular fractionation and tracer uptake methods we have demonstrated the presence of a Cl(-)-HCO3- antiport mechanism in the rat exorbital lacrimal gland. We find that outwardly directed gradients of HCO3- and of 35Cl- accelerated the flux of 36Cl- into isolated membrane vesicles. Because vesicle membrane potentials were clamped to 0 mV with K+-valinomycin, the observed anion gradient-dependent acceleration of Cl- influx could not be attributed to conductive fluxes. The antiporter had an apparent K0.5 for Cl- between 6 and 10 mM. It was sensitive to the stilbene derivatives 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). It was also sensitive to the loop diuretic furosemide, which has frequently been used in tests for NaKCl2 symporter activity. Other anions inhibited anion gradient-driven Cl- influx in the sequence SCN- greater than NO3- greater than Cl- greater than HCO3- greater than SO2-4. The density distribution of Cl(-)-HCO3- antiport activity indicated that approximately 80% of the transporter was associated with intracellular membranes, suggesting the presence of cytoplasmic pools of functional antiporters. Because several studies have already shown the presence of Na+-H+ antiporter activity in lacrimal acinar cell basolateral membranes, a cellular model for lacrimal acinar electrolyte secretion is proposed in which a parallel array of Cl- -HCO3- and Na+-H+ antiporters mediates the Na+-dependent accumulation of Cl- against its electrochemical potential gradient.
Pertussis toxin-sensitive cholinergic inhibition of somatostatin release from canine D-cells
Authors: Chan C. B. , Soll A. H.
Published: December 2017

Development of an enriched cultured cell system allowed us to investigate the mechanism of cholinergic inhibition of somatostatin release stimulated by adenosine 3',5'-cyclic monophosphate (cAMP) and Ca2+-protein kinase C-dependent pathways of cell activation. After a 24-h culture on rat tail collagen, D-cells, quantified by immunohistochemistry, were 18-fold enriched compared with unelutriated dispersed cells. Somatostatin release from cultured cells was expressed as a percent of the somatostatin released by a specific stimulus in control cells. Under basal conditions release of somatostatin was 2.3 +/- 0.6% of the total cell content. Epinephrine (1 microM) and cholecystokinin octapeptide (10 nM) increased somatostatin release to 6.98 +/- 1.25 and 10.72 +/- 1.64%, respectively. Carbachol (1 microM) completely inhibited somatostatin release stimulated by epinephrine and reduced cholecystokinin octapeptide-stimulated release to 75% of control levels. Carbachol inhibition of the response to both epinephrine and cholecystokinin octapeptide was totally prevented by 5 h of treatment of the cells with pertussis toxin (300 ng/ml). Somatostatin release in response to the diterpene forskolin (10 microM), dibutyryl cAMP (300 microM), the phorbol ester beta-phorbol 12-myristate 13-acetate (0.1 microM), and the calcium ionophore A23187 (1 microM) was also inhibited by carbachol and prevented by pertussis toxin pretreatment. The ADP-ribosylase inhibitor isonicotinamide (1 mM) selectively blocked the effect of pertussis toxin without altering other stimulatory or inhibitory responses. These data are consistent with the view that carbachol inhibits somatostatin release at guanyl nucleotide-binding protein and/or another pertussis toxin-sensitive site.
Hormonal regulation of hepatocyte tight junctional permeability
Authors: Lowe P. J. , Miyai K. , Steinbach J. H. , Hardison W. G.
Published: December 2017

We have investigated the effects of hormones on the permeability of the hepatocyte tight junction to two probes, [14C]sucrose and horseradish peroxidase, using one-pass perfused rat livers. Using a single injection of horseradish peroxidase we have demonstrated that this probe can enter bile by two pathways that are kinetically distinct, a fast pathway, which corresponds to the passage of the probe through the hepatocyte tight junctions, and a slow pathway, which corresponds to the transcytotic entry into bile. The passage of horseradish peroxidase through the hepatocyte tight junctions was confirmed by electron microscopic histochemistry. Vasopressin, epinephrine, and angiotensin II, hormones that act in the hepatocyte through the intracellular mediators calcium, the inositol polyphosphates, and diacylglycerol, increased the bile-to-perfusion fluid ratio of [14C]sucrose and the rapid entry of horseradish peroxidase into bile, indicating that the permeability of the tight junctions to these probes was increased. The effect of these hormones was dose dependent and in the cases of angiotensin II and epinephrine was inhibited by the specific inhibitors [Sar1, Thr8]angiotensin II and prazosin, respectively. Dibutyryl adenosine 3',5'-cyclic monophosphate did not affect the [14C]sucrose bile-to-perfusion fluid ratio or the fast entry of horseradish peroxidase into bile. These results suggest that the hepatocyte tight junction can no longer be considered a static system of pores separating blood from bile. It is rather a dynamic barrier potentially capable of influencing the composition of the bile.
Cholecystokinin in the regulation of intestinal motility and pancreatic secretion in dogs
Authors: Thor P. , Laskiewicz J. , Konturek P. , Konturek S. J.
Published: December 2017

Peptidal (CR-1409) and nonpeptidal (L-364,718) cholecystokinin (CCK) receptor antagonists were used to determine the possible involvement of CCK in the fasted and fed intestinal motility patterns and the related alterations in pancreatic secretion. Dogs were implanted with electrodes along the small bowel and with chronic pancreatic fistulas. In fasted dogs, the typical migrating motor complex (MMC) cycles and accompanying fluctuations in pancreatic secretion were recorded. Neither of the CCK antagonists affected these motor and secretory components of the MMC. Feeding interrupted the MMC and increased spike activity at all levels of the small bowel, and this was accompanied by a significant increase in pancreatic secretion and in plasma hormone [gastrin, CCK, and pancreatic polypeptide (PP)] levels. Both CCK antagonists significantly reduced the postprandial spike activity but failed to restore the fasted pattern. Exogenous gastrin and CCK, as well as bombesin, induced fedlike motility patterns accompanied by marked pancreatic protein secretion. These effects were completely reversed to the fasted patterns during intravenous infusion of CCK antagonists. In contrast, cholinergic stimulation (bethanechol) induced a fedlike pattern that was more resistant to CCK antagonists. We conclude that CCK does not play a major role in the fasted motility pattern and related fluctuations in pancreatic secretion but may be partly involved (by itself and by released PP) in the induction of the fed motility pattern and the postprandial stimulation of the exocrine pancreas.
Alpha 2-receptors mediate catecholamine-stimulated acid secretion in Amphiuma jejunum
Authors: Hinton C. F. , White J. F.
Published: December 2017

The receptors mediating adrenergic stimulation of acid secretion by Amphiuma jejunum were characterized in this study using alpha- and beta-adrenergic agonists and antagonists. Isolated segments of jejunum were mounted in Ussing chambers and bathed in Cl- -free (SO4(2-] medium. Shortcircuit current (Isc) and acid secretion (JH) were recorded, the latter by measuring the rate of alkalinization of the serosal medium. The beta-adrenergic receptor antagonist, propranolol (10(-4) M), had no effect on the Isc and JH stimulated by norepinephrine (NE). The alpha 2-adrenergic agonists, clonidine and UK-14,304, mimicked the effect of NE, with effective concentrations providing 50% maximal delta Isc of 2.0 X 10(-7) and 9.0 X 10(-8) M, respectively. NE added subsequently produced no greater stimulation. In contrast, the alpha 1-adrenergic agonists, phenylephrine and methoxamine, produced little stimulation of JH and Isc; NE added subsequently stimulated the Isc. The alpha 1-adrenergic antagonist prazosin had no effect on the NE-induced Isc or JH, whereas the alpha 2-adrenergic antagonist yohimbine inhibited the NE-stimulated Isc with a half-maximal effective concentration of 3.5 X 10(-7) M. Yohimbine (10(-4) M) reduced the NE-stimulated Isc by 88%, whereas the spontaneous Isc was reduced by only 12%. These results demonstrate that alpha 2-adrenergic receptors on the basolateral membrane of Amphiuma enterocytes mediate NE-enhanced, but not spontaneous, intestinal acid secretion.
Role of arachidonic acid metabolites in ethanol vasoaction in rat gastric submucosa
Authors: Yonei Y. , Wayland H. , Guth P. H.
Published: December 2017

By use of an in vivo microscopy technique in the anesthetized rat, the effect of 0.5-8.0% ethanol on gastric submucosal blood vessel diameter was studied. The direct application of ethanol onto the exposed submucosal vasculature caused a dose-dependent dilatation of the arterioles (9 +/- 3% by 2% ethanol) but had no effect on venular diameter. In rats pretreated with 5 mg/kg indomethacin subcutaneously to inhibit cyclooxygenase activity, the submucosal application of ethanol caused dose-dependent constriction of both arterioles and venules (2% ethanol decreasing diameters by 21 +/- 3 and 15 +/- 2%, respectively). This constriction by ethanol in indomethacin-pretreated rats was significantly inhibited by BW755C, a lipoxygenase inhibitor. Under these conditions, 2% ethanol had no significant effect on either arterioles or venules. In conclusion, ethanol appears to cause release of vasodilating prostaglandins and vasoconstricting leukotrienes that may mediate or modulate the microvascular response to ethanol.
Physiological, morphological, and histochemical properties of cat external anal sphincter
Authors: Krier J. , Adams T. , Meyer R. A.
Published: December 2017

The contractile properties, morphology, and the distribution of striated muscle fiber types of the external and sphincter (EAS) were determined using axial force measurements, fiber size cross-sectional area measurements, and histochemistry. Electrical stimulation of motor axons in pudendal nerve at supramaximal intensities (10 V, 0.05 ms duration) elicited twitch contractions of EAS. The time to peak force after a single pulse ranged from 37 to 42 ms. The time for relaxation to half-maximal twitch force ranged from 20 to 29 ms. Repetitive stimulation of motor axons (0.1-3.0 Hz) produced potentiation and fatigue of single twitch contractile force, suggesting that the EAS of the cat is comprised predominantly of fast-twitch muscle fibers. Confirmation of skeletal muscle fiber types was determined by histochemistry. Frozen serial cross sections of EAS were incubated to demonstrate succinic dehydrogenase (SDH) and myosin adenosine triphosphatase after alkaline preincubation (pH 10.4). Based on these reactions, muscle fibers were classified as fast glycolytic (FG) (high ATPase, low SDH), fast oxidative-glycolytic (FOG) (high ATPase, high SDH), and slow oxidative (SO) (low ATPase, high SDH). The mean percentage +/- SE of each histochemical type was the following: FG, 73.5 +/- 3.9; FOG, 22.8 +/- 3.7; and SO, 3.7 +/- 0.6. These results indicate that the predominant fiber type for the EAS is FG. The EAS of the cat is considered a nominally fast-twitch muscle.
Calbindin-D9k stimulates the calcium pump in rat enterocyte basolateral membranes
Authors: Walters J. R.
Published: December 2017

Calbindin-D9k, a vitamin D-dependent Ca2+-binding protein, is closely associated with the transcellular absorption of calcium by mammalian enterocytes. Studies were performed to determine whether physiological concentrations of calbindin-D9k altered Ca2+ transport by the ATP-dependent Ca2+ pump in rat duodenal basolateral membrane vesicles. In solutions where free Ca2+ was buffered by EGTA, only a small stimulation of Ca2+ uptake rates could be demonstrated, and it was likely that this was secondary to changes in free Ca2+ concentration. However, a threefold stimulation of uptake by 30 microM calbindin-D9k was found when EGTA-free solutions were used, and changes in free Ca2+ activity or 45Ca2+ specific activity were avoided. The affinity for Ca2+ was reduced in this system but appeared to be stimulated by either calbindin-D9k or EGTA. Other Ca2+-binding proteins that bind Ca2+ in the micromolar range were found to increase Ca2+ uptake in the absence of EGTA. These experiments suggest that one of the actions of calbindin-D9k is to stimulate the rate of extrusion of Ca2+ from the enterocyte by increasing Ca2+ transport by the Ca2+ pump.
Relation between biliary glutathione excretion and bile acid-independent bile flow
Authors: Ballatori N. , Truong A. T.
Published: December 2017

Glutathione efflux into bile of the fluorocarbon-perfused isolated rat liver was altered with eight different agents (L-buthionine-[S,R]-sulfoximine, cefamandole, sodium arsenite, phenobarbital, furosemide, nitrofurantoin, aminopyrine, and benzylamine), and correlations were established between bile flow and biliary excretion of 1) glutathione, 2) endogenous bile acids, and 3) glutathione plus bile acids. Biliary efflux of endogenous bile acids was relatively low (0.5-5 nmol.min-1.g liver-1) and was minimally affected by these agents. Biliary glutathione excretion in control livers was between 4 and 9 nmol.min-1.g-1 and in treated livers ranged from 1 to 21 nmol.min-1.g-1. For each of the various interventions, an increase or decrease in glutathione excretion was always accompanied by a change in bile flow in the same direction; however, these changes were not always directly proportional when comparisons were made between treatment groups. Nevertheless, when bile flow (microliter.min-1.g-1; ordinate) was plotted against glutathione excretion into bile for the pooled data, a significant correlation was observed that was adequately described by a straight line: y = 0.071 chi + 0.72 (r2 = 0.62, P less than 0.001). A similar function described the relation between bile flow and the sum of bile acids and glutathione in bile: y = 0.077 chi + 0.55 (r2 = 0.62, P less than 0.001). In contrast, the taurocholate- or glycocholate-induced choleresis had only minimal effects on glutathione efflux. These findings support the hypothesis that glutathione is one of the osmotic driving forces in bile acid-independent bile formation.(ABSTRACT TRUNCATED AT 250 WORDS)
Transport characteristics of glutamine in human intestinal brush-border membrane vesicles
Authors: Said H. M. , Van Voorhis K. , Ghishan F. K. , Abumurad N. , Nylander W. , Redha R.
Published: December 2017

Transport of glutamine (Gln) across the brush-border membrane of the human intestine was examined using the brush-border membrane vesicle (BBMV) technique. Osmolarity and temperature studies indicate that the uptake of Gln by BBMV is mostly the result of transport of the substrate into the intravesicular space. Transport of Gln was Na+ gradient dependent (out greater than in) with a distinct "overshoot" phenomenon. Initial rate of transport of Gln as a function of concentration was saturable both in the presence and absence of a Na+ gradient (out greater than in). Apparent Km of 1.86 and 1.36 mM and Vmax of 1,906 and 637 pmol.mg protein-1 . 7 s-1 were calculated for the Na+-dependent and the Na+-independent transport processes of Gln, respectively. The transport of [3H]Gln (0.58 mM) by the Na+-dependent and the Na+-independent processes was severely inhibited by the addition to the incubation medium of serine, asparagine, and unlabeled Gln. Inducing a relatively negative intravesicular compartment with the use of valinomycin and an outwardly directed K+ gradient or with the use of anions of different lipid permeabilities indicates that Gln transport by the Na+-dependent process is electrogenic in nature. Transport of Gln by the Na+-independent process, however, appeared to be electroneutral in nature. These results demonstrate the existence of two carrier-mediated transport processes for Gln in the human intestinal BBMV, one is Na+ dependent and the other is Na+ independent. Furthermore, the results suggest that Gln transport by the Na+-dependent process probably occurs by a Gln-Na+ cotransport mechanism.
Gastric resistance to acid: is the "mucus-bicarbonate barrier" functionally redundant?
Authors: Wallace J. L.
Published: December 2017

The functional importance of the "mucus-bicarbonate barrier" in protecting the gastric mucosa against injury by acid or pepsin was examined using an ex vivo gastric chamber preparation in the rat. Conditions were created such that the effectiveness of a mucus-stabilized pH gradient on the mucosal surface would be minimized. Thus solutions of hydrochloric acid of pH 1.3 or 0.8 were applied to the mucosal surface and continually stirred for 60 min. By use of an antimony pH microelectrode, these concentrations of acid were shown to dissipate the pH gradient on the mucosal surface within 5 min. The effects of addition of the mucolytic agents, pepsin or N-acetylcysteine, to both acid solutions were also assessed. Finally, the ability of the mucosa to resist injury by acid after disruption of the surface epithelium (with hypertonic saline) was examined. Exposure to the acid solutions, with or without added mucolytic agents, was without damaging effects on the mucosa, as assessed macroscopically, histologically, or by measurement of transmucosal potential difference and luminal protein concentration. Conversely, disruption of the surface epithelium rendered the mucosa significantly more susceptible to the damaging actions of acid. These results therefore demonstrate that under conditions in which a pH gradient on the mucosal surface was no longer detectable, the mucosa was resistant to injury by acid. In the undamaged rat stomach, therefore, the mucus-bicarbonate barrier may be functionally redundant.
Na+-H+ exchange activity in rat hepatocytes: role in regulation of intracellular pH
Authors: Renner E. L. , Lake J. R. , Persico M. , Scharschmidt B. F.
Published: December 2017

Amiloride-sensitive Na+-H+ exchange has been identified in basolateral membrane vesicles from rat liver, but little is currently known about its regulation or its role in maintenance of resting intracellular pH (pHi) in intact hepatocytes. We have assessed Na+-H+ exchange activity in isolated or cultured rat hepatocytes in nominally HCO3- free solution under basal conditions and after intracellular acidification by an NH4Cl pulse by measuring 1) pHi, using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxy fluorescein, 2) net H+ efflux by pH-stat titration, and 3) amiloride-inhibitable 22Na uptake. Under resting conditions, Na+-H+ exchange did not contribute measurably to Na+ uptake and accounted for less than 20% of net H+ efflux. Hepatocyte pHi averaged 7.07 +/- 0.03, significantly above H+ electrochemical equilibrium (6.92 +/- 0.08) determined using an electrogenic proton ionophore. Transient removal of extracellular Na+ or exposure to amiloride reversibly lowered pHi by 0.09 +/- 0.01 and 0.12 +/- 0.03 pH units, respectively, within 5-10 min. After intracellular acidification by an NH4Cl pulse, Na+ uptake rate increased about twofold, the increase being entirely amiloride inhibitable. Net H+ efflux increased about threefold, and 70% of the increase was amiloride inhibitable. Recovery of pHi after an NH4Cl pulse was reversibly blocked by exposure to amiloride or removal of Na+. Na+-H+ exchange activity (calculated from the rate of change in pHi and intracellular buffering capacity) was inversely related to pHi and was estimated to approach zero at pHi 7.25-7.50.(ABSTRACT TRUNCATED AT 250 WORDS)
Opioid receptors and the initiation of migrating myoelectric complexes in dogs
Authors: Telford G. L. , Condon R. E. , Szurszewski J. H.
Published: December 2017

The role of endogenous opioids and opioid receptors in the control of migrating myoelectric complexes (MMCs) was studied in conscious dogs implanted with silver-silver chloride electrodes. In normal fasted dogs, MMC cycle times were 103 +/- 7 min in the duodenum. During naloxone infusion (1-2 mg/kg iv, then 0.2-1.0 mg.kg-1.h-1 iv) cycle times increased to 219 +/- 29 min (P less than 0.01). Naloxone (2 mg/kg iv, then 1 mg.kg-1.h-1 iv) had no effect on the response of the small intestine to bethanecol (5 mg sc) or to feeding. Pretreatment with naloxone (2 mg/kg iv) 5 min before the administration of motilin (400-500 micrograms/kg iv) did not block the initiation of MMCs by motilin. In separate experiments, animals were pretreated with the positive or negative isomer of the opioid receptor antagonist WIN-44,441 (0.2 mg/kg iv) 5 min before morphine administration. The negative isomer binds to opioid receptors whereas the positive isomer does not. The negative but not the positive isomer antagonized all effects of morphine on intestinal myoelectric activity. These studies suggest that endogenous opioids and opioid receptors may play a role in control of the initiation of MMCs and that motilin and exogenous opioids act via different mechanisms to initiate MMCs.