bluuebunny/crossref_metadata_2025 huggingface dataset:
Human neutrophils facilitate tumor cell transendothelial migration
Authors: Wu Qiong Di , Wang Jiang Huai , Condron Claire , Bouchier-Hayes David , Redmond H. Paul
Published: December 2017

Tumor cell extravasation plays a key role in tumor metastasis. However, the precise mechanisms by which tumor cells migrate through normal vascular endothelium remain unclear. In this study, using an in vitro transendothelial migration model, we show that human polymorphonuclear neutrophils (PMN) assist the human breast tumor cell line MDA-MB-231 to cross the endothelial barrier. We found that tumor-conditioned medium (TCM) downregulated PMN cytocidal function, delayed PMN apoptosis, and concomitantly upregulated PMN adhesion molecule expression. These PMN treated with TCM attached to tumor cells and facilitated tumor cell migration through different endothelial monolayers. In contrast, MDA-MB-231 cells alone did not transmigrate. FACScan analysis revealed that these tumor cells expressed high levels of intercellular adhesion molecule-1 (ICAM-1) but did not express CD11a, CD11b, or CD18. Blockage of CD11b and CD18 on PMN and of ICAM-1 on MDA-MB-231 cells significantly attenuated TCM-treated, PMN-mediated tumor cell migration. These tumor cells still possessed the ability to proliferate after PMN-assisted transmigration. These results indicate that TCM-treated PMN may serve as a carrier to assist tumor cell transendothelial migration and suggest that tumor cells can exploit PMN and alter their function to facilitate their extravasation.
Protein kinase C-mediated desensitization of the neurokinin 1 receptor
Authors: Déry Olivier , Defea Kathryn A. , Bunnett Nigel W.
Published: December 2017

An understanding of the mechanisms that regulate signaling by the substance P (SP) or neurokinin 1 receptor (NK1-R) is of interest because of their role in inflammation and pain. By using activators and inhibitors of protein kinase C (PKC) and NK1-R mutations of potential PKC phosphorylation sites, we determined the role of PKC in desensitization of responses to SP. Activation of PKC abolished SP-induced Ca2+ mobilization in cells that express wild-type NK1-R. This did not occur in cells expressing a COOH-terminally truncated NK1-R (NK1-Rδ324), which may correspond to a naturally occurring variant, or a point mutant lacking eight potential PKC phosphorylation sites within the COOH tail (NK1-R Ser-338, Thr-339, Ser-352, Ser-387, Ser-388, Ser-390, Ser-392, Ser-394/Ala, NK1-RKC4). Compared with wild-type NK1-R, the t ½ of SP-induced Ca2+mobilization was seven- and twofold greater in cells expressing NK1-Rδ324 and NK1-RKC4, respectively. In cells expressing wild-type NK1-R, inhibition of PKC caused a 35% increase in the t ½ of SP-induced Ca2+mobilization. Neither inhibition of PKC nor receptor mutation affected desensitization of Ca2+ mobilization to repeated challenge with SP or SP-induced endocytosis of the NK1-R. Thus PKC regulates SP-induced Ca2+ mobilization by full-length NK1-R and does not regulate a naturally occurring truncated variant. PKC does not mediate desensitization to repeated stimulation or endocytosis of the NK1-R.
Point mutations in the post-M2 region of human α-ENaC regulate cation selectivity
Authors: Ji Hong-Long , Parker Suzanne , Langloh Anne Lynn B. , Fuller Catherine M. , Benos Dale J.
Published: December 2017

We tested the hypothesis that an arginine-rich region immediately following the second transmembrane domain may constitute part of the inner mouth of the epithelial Na+ channel (ENaC) pore and, hence, influence conduction and/or selectivity properties of the channel by expressing double point mutants in Xenopus oocytes. Double point mutations of arginines in this post-M2 region of the human α-ENaC (α-hENaC) led to a decrease and increase in the macroscopic conductance of αR586E,R587Eβγ- and αR589E,R591Eβγ-hENaC, respectively, but had no effect on the single-channel conductance of either double point mutant. However, the apparent equilibrium dissociation constant for Na+ was decreased for both αR586E,R587Eβγ- and αR589E,R591Eβγ-hENaC, and the maximum amiloride-sensitive Na+ current was decreased for αR586E,R587Eβγ-hENaC and increased for αR589E,R591Eβγ-hENaC. The relative permeabilities of Li+ and K+ vs. Na+ were increased 11.25- to 27.57-fold for αR586E,R587Eβγ-hENaC compared with wild type. The relative ion permeability of these double mutants and wild-type ENaC was inversely related to the crystal diameter of the permeant ions. Thus the region of positive charge is important for the ion permeation properties of the channel and may form part of the pore itself.
Protein kinase Cɛ contributes to regulation of the sarcolemmal Na+-K+ pump
Authors: Buhagiar Kerrie A. , Hansen Peter S. , Bewick Nerida L. , Rasmussen Helge H.
Published: December 2017

A reduction in angiotensin II (ANG II) in vivo by treatment of rabbits with the angiotensin-converting enzyme inhibitor, captopril, increases Na+-K+ pump current ( I p) of cardiac myocytes. This increase is abolished by exposure of myocytes to ANG II in vitro. Because ANG II induces translocation of the ɛ-isoform of protein kinase C (PKCɛ), we examined whether this isozyme regulates the pump. We treated rabbits with captopril, isolated myocytes, and measured I p of myocytes voltage clamped with wide-tipped patch pipettes. I p of myocytes from captopril-treated rabbits was larger than I p of myocytes from controls. ANG II superfusion of myocytes from captopril-treated rabbits decreased I p to levels similar to controls. Inclusion of PKCɛ-specific blocking peptide in pipette solutions used to perfuse the intracellular compartment abolished the effect of ANG II. Inclusion of ψɛRACK, a PKCɛ-specific activating peptide, in pipette solutions had an effect on I p that was similar to that of ANG II. There was no additive effect of ANG II and ψɛRACK. We conclude that PKCɛ regulates the sarcolemmal Na+-K+ pump.
Escherichia coli as an expression system for K+ transport systems from plants
Authors: Uozumi Nobuyuki
Published: December 2017

The value of the Escherichia coli expression system has long been established because of its effectiveness in characterizing the structure and function of exogenously expressed proteins. When eukaryotic membrane proteins are functionally expressed in E. coli, this organism can serve as an alternative to eukaryotic host cells. A few examples have been reported of functional expression of animal and plant membrane proteins in E. coli. This mini-review describes the following findings: 1) homologous K+ transporters exist in prokaryotic cells and in eukaryotic cells; 2) plant K+ transporters can functionally complement mutant K+ transporter genes in E. coli; and 3) membrane structures of plant K+ transporters can be elucidated in an E. colisystem. These experimental findings suggest the possibility of utilizing the E. coli bacterium as an expression system for other eukaryotic membrane transport proteins.
Ischemia disrupts myosin Iβ in renal tubules
Authors: Boyd-White Judy , Srirangam Anjaiah , Goheen Michael P. , Wagner Mark C.
Published: December 2017

In these studies we have examined rat kidneys biochemically and microscopically to determine where myosin Iβ is located before, during, and after an acute ischemic injury. Myosin Iβ is present in multiple tubule segments including the brush border (BB) of the proximal tubule cell (PTC). Its distribution is severely altered by a 15-min renal artery clamp. Myosin Iβ is present in the urine during reflow and is found in the numerous cellular blebs arising from the damaged PTC and other tubules. Two hours of reflow result in a decrease in BB myosin Iβ staining and an increase in its cytoplasmic staining. Interestingly, the return of the F-actin in the BB precedes the return of the myosin Iβ, suggesting that this myosin I isoform may not play a role in rebuilding the microvilli after an ischemic injury. A nonstructural role for this myosin, such as transport or channel regulation, is supported by its presence in many tubule segments, all of which have transport and channel requirements but do not all contain microvilli.
K-Cl cotransport modulation by intracellular Mg in erythrocytes from mice bred for low and high Mg levels
Authors: De Franceschi Lucia , Villa-Moruzzi Emma , Fumagalli Laura , Brugnara Carlo , Turrini Franco , Motta Roland , Veghini Emanuela , Corato Cristina , Alper Seth L. , Berton Giorgio
Published: December 2017

Mg is an important determinant of erythrocyte cation transport system(s) activity. We investigated cation transport in erythrocytes from mice bred for high (MGH) and low (MGL) Mg levels in erythrocytes and plasma. We found that K-Cl cotransport activity was higher in MGL than in MGH erythrocytes, and this could explain their higher mean corpuscular hemoglobin concentration, median density, and reduced cell K content. Although mouse KCC1 protein abundance was comparable in MGL and MGH erythrocytes, activities of Src family tyrosine kinases were higher in MGH than in MGL erythrocytes. In contrast, protein phosphatase (PP) isoform 1α (PP1α) enzymatic activity, which has been suggested to play a positive regulatory role in K-Cl cotransport, was lower in MGH than in MGL erythrocytes. Additionally, we found that the Src family kinase c-Fgr tyrosine phosphorylates PP1α in vitro. These findings suggest that in vivo downregulation of K-Cl cotransport activity by Mg is mediated by enhanced Src family kinase activity, leading to inhibition of the K-Cl cotransport stimulator PP1.
LabHEART: an interactive computer model of rabbit ventricular myocyte ion channels and Ca transport
Authors: Puglisi José L. , Bers Donald M.
Published: December 2017

An interactive computer program, LabHEART, was developed to simulate the action potential (AP), ionic currents, and Ca handling mechanisms in a rabbit ventricular myocyte. User-oriented, its design allows switching between voltage and current clamp and easy on-line manipulation of key parameters to change the original formulation. The model reproduces normal rabbit ventricular myocyte currents, Ca transients, and APs. We also changed parameters to simulate data from heart failure (HF) myocytes, including reduced transient outward ( I to) and inward rectifying K currents ( I K1), enhanced Na/Ca exchange expression, and reduced sarcoplasmic reticulum Ca-ATPase function, but unaltered Ca current density. These changes caused reduced Ca transient amplitude and increased AP duration (especially at lower frequency) as observed experimentally. The model shows that the increased Na/Ca exchange current ( I NaCa) in HF lowers the intracellular [Ca] threshold for a triggered AP from 800 to 540 nM. Similarly, the decrease in I K1reduces the threshold to 600 nM. Changes in I tohave no effect. Combining enhanced Na/Ca exchange with reduced I K1 (as in HF) lowers the threshold to trigger an AP to 380 nM. These changes reproduce experimental results in HF, where the contributions of different factors are not readily distinguishable. We conclude that the triggered APs that contribute to nonreentrant ventricular tachycardia in HF are due approximately equally (and nearly additively) to alterations in I NaCa and I K1. A free copy of this software can be obtained at http://www.meddean.luc.edu/lumen/DeptWebs/physio/bers.html .
Episodic growth hormone secretory patterns in sheep: relationship to gonadal steroid hormones.
Authors: Davis S L , Ohlson D L , Klindt J , Anfinson M S
Published: December 2017

The influence of anabolic steroids on growth hormone (GH) secretion in ruminants remains unclear, perhaps because of the dynamic nature of GH secretion. In the present study, blood samples were obtained at 15-min intervals for 12 h from intact ram lambs, ram lambs castrated postpubertally, and castrated ram lambs treated with either testosterone propionate (TP) or diethylstilbestrol (DES). Intact rams exhibited GH secretory episodes of greater (P less than 0.01) amplitude than did castrated lambs. Similarly, mean base-line and mean overall GH concentrations were higher (P less than 0.01) in rams than in castrates. Treatment of castrates with either TP or DES resulted in increased base-line (P less than 0.05) and overall (P less than 0.05) GH concentrations compared to untreated castrates. Although amplitude of GH spikes was larger in TP and DES groups, this difference was not statistically significant (P greater than 0.05). Because numerous studies have demonstrated that intact rams and castrates treated with TP or DES grow faster than untreated castrates, the data in the present study support the hypothesis that the anabolic action of androgens and estrogens is due, at least in part, to their influence on GH secretion.
Cholinergic-adrenergic interactions on intestinal ion transport.
Authors: Tapper E J , Powell D W , Morris S M
Published: December 2017

The autonomic control of intestinal electrolyte transport has been investigated in the in vitro, short-circuited rabbit ileum with varying doses of carbachol and with neuroeffector blocking agents. Low-dose carbachol (less than 10(-6) M) and high-dose carbachol (greater than 10(-4) M) had different effects on Na and Cl transport. Low-dose carbachol caused a transient increase in the potential difference and short-circult current, stimulated Cl secretion, and inhibited the residual flux (probably HCO3 secretion). This is a muscarinic response since it is inhibited by atropine (10(-6) M). After an initial increase of the potential difference and short-circuit current, high-dose carbachol reduced these electrical parameters, stimulated Na and Cl absorption, and abolished the residual flux. This is a nicotinic response since it is inhibited by hexamethonium (10(-5) M). This nicotinic response is identical to that reported by others with alpha-adrenergic agents and it was inhibited also by phentolamine (10(-7) M). We propose that high-dose carbachol stimulates nicotinic receptors on postganglionic sympathetic fibers present in our preparations causing a release of catecholamines and a resulting alpha-adrenergic response by the intestinal epithelial cell. The physiological significance of this response in the gut remains to be determined.
A basic relationship between gastric and duodenal motilities in chickens.
Authors: Roche M , Ruckebusch Y
Published: December 2017

Chickens were chronically fitted with a duodenal cannula and pairs of electrodes implanted in the wall of the muscular stomach, duodenum and ileum. Smooth muscle electrical activity was recorded in both fed and fasted conditions under a 12--12 h dark-light schedule. Two major patterns of activity were identified. The first consisted of spike bursts that propagated rapidly either aborally from the stomach or orally from the ileum. Aborad-propagated spike bursts were most frequent during the daytime; this circadian variation was abolished by vagotomy, which also increased the frequency of orad-propagated spike bursts. The second pattern was characterized by periods of repetitive spike bursts lasting 3--10 min and spreading aborally at a slower rate. In the fasted chicken, the daily frequency was increased and the period of repetitive spike bursts resembled the prolonged bursts of spike potentials recorded in the feline small intestine. The results suggest that the propulsion of digesta might depend on the ratio of spike bursts moving aborally from the stomach to those moving orally from the ileum. Both factors were influenced by the level of stomach activity.
A reciprocal adrenergic-cholinergic axoaxonic synapse in the mammalian gut.
Authors: Manber L , Gershon M D
Published: December 2017

Simultaneous stimulation of perivascular nerves inhibited the release of acetylcholine from stimulated cholinergic nerves of the rabbit jejunum. Adrenergic nerves were responsible for this inhibition because it did not occur in animals previously injected with 6-hydroxydopamine. Acetylcholine inhibited the release of transmitter from stimulated adrenergic axons; this effect was blocked by atropine. Since atropine enhanced the release of adrenergic transmitter when both adrenergic and cholinergic nerves were activated simultaneously (at 4.0 Hz), it seems likely that cholinergic nerves also inhibit release of norepinephrine (NE). Radioautographic examination of the myenteric plexus, incubated with tritiated NE, revealed a striking marginal distribution of adrenergic axons around the periphery of the myenteric plexus. Ultrastructural studies, with KMnO4 used to identify adrenergic terminal varicosities, confirmed this distribution and also revealed complexes formed between the terminal varicosities of adrenergic and probable cholinergic axons. The component varicosities forming these complexes contacted one another with no intervening Schwann cell elements. It is concluded that there is a reciprocal axoaxonic synapse between adrenergic and cholinergic neurons in the mammalian myenteric plexus.
Cobalt but not hypoxia stimulates PDGF gene expression in rats
Authors: Bucher M. , Sandner P. , Wolf K. , Kurtz A.
Published: December 2017

This study was done to investigate the influence of different forms of acute tissue hypoxia on the expression of platelet-derived growth factor (PDGF) A chain (PDGF-A) and PDGF B chain (PDGF-B) genes in different rat organs. We found that acute normobaric hypoxia (8% O2), carbon monoxide inhalation (0.1% CO), or lowering the hematocrit to 12% for 6 h had no effect on PDGF-A or PDGF-B gene expression in lung, heart, kidney, and liver of Sprague-Dawley rats. Subcutaneous administration of cobaltous chloride dose dependently increased PDGF-B mRNA by 125% in lungs, by 60% in kidneys, but not in heart and liver. These findings suggest that acute tissue hypoxygenation is not a significant stimulus for PDGF-A and PDGF-B gene expression in these major rat organs. Cobalt appears to cause a tissue-specific increase of PDGF-B gene expression.
Effects of oral vs. i.v. glucose administration on splanchnic and extrasplanchnic O2 uptake and blood flow
Authors: Brundin T. , Branstrom R. , Wahren J.
Published: December 2017

The metabolic and circulatory responses to intravenous or oral administration of glucose (75 g) were studied in healthy subjects. Pulmonary oxygen uptake increased promptly after oral but not during intravenous glucose infusion. The average 2-h rise above basal in whole body oxygen uptake was 8 +/- 1% (P < 0.001) after oral glucose and 3 +/- 1% (P < 0.05) during intravenous glucose infusion. After oral glucose, splanchnic oxygen uptake rose initially by approximately 15% (P < 0.01) and then declined; its average 2-h postprandial level was not significantly higher than that in the basal state. During intravenous glucose, splanchnic oxygen uptake decreased gradually during the first 75 min, reaching a level approximately 25% below basal (P < 0.05). Oxygen consumption by extrasplanchnic tissues rose significantly and to a similar extent (8%, 2 h average) with both intravenous and oral glucose. Splanchnic blood flow increased significantly after oral but not during intravenous glucose. It is concluded that 1) intravenous infusion and oral glucose administration elicit extrasplanchnic thermogenic effects of similar magnitude, 2) during intravenous glucose infusion, the extrasplanchnic thermogenic effect is counterbalanced by a simultaneous reduction in splanchnic oxygen uptake, resulting in a minimal (3%) net rise in whole body oxygen uptake, and 3) oral glucose ingestion but not intravenous glucose infusion increases the splanchnic blood flow.
Acetaminophen glucuronidation accurately reflects gluconeogenesis in fasted dogs
Authors: Schwenk W. F. , Kahl J. C.
Published: December 2017

To assess whether acetaminophen glucuronide accurately reflects uridyl diphosphate-glucose (UDP-glucose) derived from gluconeogenesis during fasting, three mongrel dogs received infusions of [U-14C]lactate, [1-13C]galactose, and [6-3H]glucose (after fasting overnight or for 2.5 days). After initiation of the isotopes (3 h), acetaminophen was given, and the urinary acetaminophen glucuronide was isolated. The mean plasma [14C]glucose specific activity (SA) was similar to the mean urinary acetaminophen glucuronide SA both after fasting overnight [299 +/- 19 vs. 296 +/- 14 disintegrations.min-1 (dpm).mumol-1, respectively] and after 2.5 days of fasting (511 +/- 8 vs. 562 +/- 32 dpm/mumol, respectively). Mean plasma glucose flux calculated using [6-3H]glucose decreased (P < 0.05) with two additional days of fasting (18.7 +/- 1.2 vs. 13.6 +/- 0.6 mumol.kg-1.min-1), as did intrahepatic (P < 0.05) UDP-glucose flux measured using [1-13C]galactose (8.6 +/- 0.7 vs. 5.5 +/- 0.3 mumol.kg-1.min-1). We conclude that, in fasted dogs, plasma glucose and UDP-glucose, as sampled by acetaminophen, equally reflect gluconeogenesis and appear to come from the same pool of glucose 6-phosphate. In addition, cycling of glucose moieties through UDP-glucose and glycogen decreases with an increased period of fasting.
Insulin resistance caused by hepatic cholinergic interruption and reversed by acetylcholine administration
Authors: Xie H. , Lautt W. W.
Published: December 2017

The role of hepatic parasympathetic nerves in insulin effectiveness was evaluated in fed anesthetized rats. Insulin sensitivity was assessed using a modified euglycemic clamp to quantitate the amount of glucose required to maintain euglycemia over 60 min after administration of insulin (50 mU/kg). With normal innervation, intraportal infusions of acetylcholine (ACh, 2.5 micrograms.kg-1.min-1) did not alter insulin sensitivity, but intraportal venous atropine (3 mg/kg) reduced insulin sensitivity (49.4 +/- 5.8%, P < 0.001, n = 7). Liver denervation resulted in reduction of insulin responsiveness by 70.8 +/- 5.8% (P < 0.001, n = 8), which was fully (96.8 +/- 12.5%) reversed by ACh. ACh into the portal vein reversed insulin resistance produced by denervation, but intravenous ACh was without effect, thus showing that the liver was the site of ACh action. Regression analysis suggests that some component of insulin response is not dependent on hepatic cholinergic nerve effects but that virtually all of the variability in response to insulin in normal fed rats tested under these conditions could be accounted for by variability in the hepatic parasympathetic-dependent insulin sensitivity. These data suggest a major role for hepatic parasympathetic nerves in regulation of whole body clearance of glucose in response to insulin.
Intact glucose transport in morphologically altered denervated skeletal muscle from quadriplegic patients
Authors: Aksnes A. K. , Hjeltnes N. , Wahlstrom E. O. , Katz A. , Zierath J. R. , Wallberg-Henriksson H.
Published: December 2017

The present study was undertaken to investigate the nature of the whole body insulin resistance that characterizes patients with complete cervical spinal cord lesion. Nine patients with C5-C7 lesions and ten age-matched healthy individuals were studied. Whole body insulin-mediated glucose utilization was reduced by 43% in the quadriplegic patients compared with the controls (P < 0.001). In the quadriplegic patients, lean body mass corresponded to 66 +/- 3% of total body mass. Despite whole body insulin resistance, in isolated vastus lateralis muscle, basal and insulin-stimulated 3-O-methylglucose transport, as well as protein expression of the insulin or exercise-regulatable glucose transporter, GLUT-4, and glycogen content were comparable between the patients and controls. Strikingly, muscle fiber area was reduced by 44% (P < 0.05), percentage of type IIb fibers was increased (P < 0.01), and there was a complete loss of type I fibers in the patients. In conclusion, the dissociation between whole body insulin-mediated glucose uptake and skeletal muscle glucose transport in quadriplegic patients primarily reflects the decreased muscle mass. Furthermore, these findings demonstrate a remarkable capacity of skeletal muscle to maintain an intact glucose transport system despite severe morphological alterations.
Nutrient and bowel segment dependency of human intestinal control of gastric secretion
Authors: Owyang C. , Miller L. J. , Malagelada J. R. , Go V. L.
Published: December 2017

The gastric secretory effects of protein, fat, and carbohydrate infused at different levels of the small bowel were investigated in seven healthy subjects. Similar caloric loads (53.4 kcal) of protein (essential amino acids), lipid (oleic acid), and carbohydrate (glucose) in isomolar (280 mosmol/l) similar pH (7.4) solutions were infused into 60-cm segments of small bowel (isolated between two occlusive balloons), located distal to the ligament of Treitz (proximal), proximal to the ileocecal valve (distal), and between the two (middle). A submaximal gastric secretory background was provided by continuous intravenous pentagastrin. Protein stimulated acid secretion in the proximal (increase of 8.7 meq/h, representing 84 +/- 5% of control level) and middle (increase of 1.9 meq/h, representing 16 +/- 2% of control level) segments, while it inhibited acid secretion when infused into the distal segment (decrease of 3.7 meq/h, representing 33 +/- 4% of control level). In contrast, both lipid and carbohydrate inhibited acid secretion similarly (33-38% of control level) at all levels of the bowel. The different effects of protein at different levels of the bowel could not be explained by differences in serum gastrin, different degrees of absorption, or different postabsorptive levels of alpha-amino nitrogen. This suggests the presence of hormonal (nongastrin) or neural mechanisms in the proximal bowel to stimulate acid secretion and/or in the distal bowel to inhibit acid secretion. Thus, factors that determine specific nutrient loads to specific segments of bowel can have important physiological effects on gastric acid secretion.
Exclusion phenomenon in the liver interstitium
Authors: Barrowman J. A. , Perry M. A. , Kvietys P. R. , Granger D. N.
Published: December 2017

Measurements were made of hepatic interstitial fluid volume and the proportion of that space occupied by 125I-labeled lactoglobulin, albumin, and gamma-globulin in anesthetized cats. 51Cr-red blood cells and 99mTc-diethylenetriaminepentaacetic acid were used to estimate tissue blood volume and extracellular volume, respectively. Hepatic lymph was assumed to represent the interstitial fluid of the liver. The degree of exclusion of each protein increased with increasing molecular size. At normal hepatic venous pressures, the excluded volume fraction for cat albumin was 0.41. Elevation of hepatic venous pressure by 12.5 mmHg caused a fourfold increase in hepatic lymph flow with an increase in interstitial volume and a reduction in albumin exclusion. When the exclusion of heterologous (human) albumin was studied in the cat liver, much higher values were obtained than with homologous albumin. This effect may be due to polymerization of commercial human albumin on storage.
Electrically coupled intrinsic responses of feline lower esophageal sphincter
Authors: Reynolds J. C. , Ouyang A. , Cohen S.
Published: December 2017

Intraluminal pressures and serosal myoelectric activity were recorded simultaneously from the esophagus, lower esophageal sphincter (LES), and stomach of chloralose-anesthetized cats. The LES demonstrated intermittent spike activity basally without slow waves and was distinct from esophagus and fundus. LES spike activity was not correlated with basal sphincter pressure. Dose-dependent increases in both spikes and pressure occurred with bethanechol, phenylephrine, or pentagastrin. Increased spike activity preceded the onset of the pressure rise and peaked during the rise in pressure. Changes in LES pressure and spike activity following these agents were correlated closely (r = 0.92, P less than 0.01). Atropine and isoproterenol inhibited pressure and spike activity similarly. Intrinsic reflexes to endogenous stimuli gave parallel spike and pressure changes. Distal esophageal acidification produced an increase in LES pressure that was correlated with increased spike activity. LES spike activity and pressure were inhibited similarly by antral distension or gastric acidification. Dissection of the distal esophagus from the diaphragm or bilateral cervical vagotomy had no effect on either LES spike activity or pressure. These studies indicate that a) LES myoelectric activity consists of spike discharges that are not correlated to resting pressure, b) abrupt changes in sphincter pressure following either intrinsic reflexes or neurohormonal agents are closely associated with similar changes in spike activity, and c) spike activity and sphincter pressure are intrinsic to the LES.
Coupled sodium-chloride transport by rabbit ileal brush-border membrane vesicles
Authors: Fan C. C. , Faust R. G. , Powell D. W.
Published: December 2017

Uptake of Na and Cl into brush-border membrane vesicles isolated from rabbit ileal epithelial cells was investigated with a rapid filtration technique using 22Na and 36Cl as tracers. The rank order of anion dependence for Na uptake in the absence of anion gradients was SCN greater than NO3 greater than gluconate. The sequence of cation specificity for Cl uptake was Na congruent to Li greater than K greater than choline. The transport of Na and Cl were both inhibited by harmaline, furosemide, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, and 4,4'-diisothiocyano-2,2'-stilbene disulfonic acid. Carrier mediation of Cl-stimulated Na transport was suggested by the competition for 22Na uptake with increasing concentrations of unlabeled Na in the presence of Cl but not when gluconate was the counterion. Chloride-dependent Na uptake had an apparent Km of 4.5 mM and a Vmax of 20 nmol . mg prot-1 . 15 s-1. Na-H exchange and Cl-OH (or HCO3) exchange were also demonstrated in these vesicles. These findings confirm the presence of an electrically neutral carrier-mediated, Na-Cl-coupled transport process in the apical cell membrane of rabbit ileal epithelial cells. The nature of the coupling of Na to Cl transport, i.e., NaCl symport or a process that combines Na-H antiport with Cl-OH (or HCO3) antiport, remains to be determined.
Analyzing tracer disappearance curves to study hepatic transport kinetics
Authors: Forker E. L. , Luxon B. A.
Published: December 2017

This paper is devoted to a discussion of recent developments in the compartmental analysis of hepatic transport, especially the interpretation of tracer disappearance curves recorded from the reservoir of an isolated perfused liver preparation. The emphasis is on the advantages that this approach enjoys over other mathematical models, and a critical review of alternative methods is therefore included. The mathematical equations are largely suppressed, however, having appeared elsewhere in detail.
Saturation kinetics in hepatic drug removal: a statistical approach to functional heterogeneity
Authors: Bass L.
Published: December 2017

Extraction of drugs and other substrates from blood passing through the intact liver (or other capillary beds), inferred from samples taken at the organ inlet and outlet, is influenced by two kinds of heterogeneity of capillaries: transverse and longitudinal with respect to the direction of blood flow. The transverse heterogeneity is exemplified by arteriovenous shunts of the extracting system; the longitudinal one by zones of liver function. These two clinically interesting examples are among transverse and longitudinal distributions of capillary properties that can be inferred from the way the organ transforms the influx of a substance (or of a pair of substances interacting via liver cells) into the outflux over a range of input concentrations or of rates of blood flow. Mathematical and statistical ideas recently developed to implement this program in terms of saturation kinetics of uptake are reviewed and elucidated in relation to key experiments, data analysis, and statistical hypothesis testing.
Effects of cardiac tamponade on colonic hemodynamics and oxygen uptake
Authors: Bulkley G. B. , Kvietys P. R. , Perry M. A. , Granger D. N.
Published: December 2017

The local hemodynamic response of the innervated but vascularly isolated colon to decreased systemic perfusion induced by cardiac tamponade was studied in anesthesized dogs as a model of nonocclusive mesenteric ischemia. Increasing levels of pericardial pressure caused progressive decreases in colonic blood flow associated with substantial increases in colonic vascular resistance. These increases in local colonic resistance were proportionately larger than concurrent increases in systemic resistance. The disproportionate response of the colonic resistance vessels was not diminished by colonic (sympathetic) denervation. Reductions of blood flow to 30 ml . min-1 . 100 g-1 resulted in compensatory increases in colonic oxygen extraction such that colonic oxygen consumption remained constant (flow independent) at about 1.5 ml . min-1 . 100 g-1. At blood flows below 30 ml . min-1 . 100 g-1 colonic oxygen consumption was markedly dependent on blood flow. This fundamental relation of colonic oxygen consumption to blood flow was the same whether ischemia was induced by cardiac tamponade, partial mechanical arterial occlusion, or vasoconstrictor (norepinephrine or digoxin) infusion. Furthermore, this relationship was not altered by vasodilation with isoproterenol after the induction of ischemia by any of the above means.
Mucosal calcium uptake by rat cecum: identity with transcellular calcium absorption
Authors: Nellans H. N. , Goldsmith R. S.
Published: December 2017

Unidirectional intestinal calcium uptake (JCame) at the mucosal surface of rat cecum was investigated in vitro with intact tissue. Uptake is linear for 2–3 min with no indication of rapid calcium binding. Kinetic parameters reveal a maximal velocity of 333 nmol . cm-2 . h-1 with a half-maximal concentration of 0.98 mM. High-calcium diet decreased JCame by more than 60% with respect to both control and low-calcium diets; 1 mM N-ethylmaleimide caused a similar reduction. The activation energy of JCame is significantly less than that of transepithelial mucosal-to-serosal calcium absorption. Mucosal uptake was compared with transepithelial calcium fluxes in rat cecum and revealed a 1:1 correlation over a wide range of transport rates. These results are interpreted to implicate a feedback control system between basolateral calcium efflux and brush-border calcium influx.
Horseradish peroxidase transport across rabbit jejunum and Peyer's patches in vitro
Authors: Ducroc R. , Heyman M. , Beaufrere B. , Morgat J. L. , Desjeux J. F.
Published: December 2017

Uptake and transport of horseradish peroxidase (HRP) have been observed in both Peyer's patches (PP) and jejunal epithelium (JE), and the quantities transported across each tissue were compared. Steady-state was reached much faster in PP than in JE. In Ringer solution, no significant difference was found between the HRP fluxes conveyed through PP and JE. In the presence of 10 mM glucose, slight net secretion was observed in JE but not in PP. In both tissues, the transport mechanism was shown to be sensitive to metabolic inhibitors. By contrast, in PP, ammonia did not significantly enhance intact HRP fluxes. Intracellular transfer and catabolism were estimated by measuring transepithelial fluxes of tritiated HRP. In PP, fluxes from mucosa to serosa and from serosa to mucosa were both greatly reduced (9.18 +/- 3.9 and 10.5 +/- 5.1 pmol X h-1 X cm-2, respectively) compared with JE (106.02 +/- 16 and 31.3 +/- 9.3). These results indicate that intact HRP fluxes are similar in PP and JE, but that tritiated HRP fluxes (intact plus degraded HRP fluxes) are smaller in PP. Together, these results suggest that the specific characteristics of HRP transport across PP are fast uptake and reduced degradation.
Effect of bile and bile acids on binding of intrinsic factor to cobalamin and intrinsic factor-cobalamin complex to ileal receptor
Authors: Seetharam B. , Jimenez M. , Alpers D. H.
Published: December 2017

Human bile or commercially available bile acids bind [57Co]cobalamin (Cbl) due to the presence of "R"-type binders, which are normally present in the former and present as a contaminant in the latter. The competition of these R proteins for the binding of Cbl by intrinsic factor (IF) could explain the in vivo inhibition attributed previously to the bile acids themselves. R protein seems to be involved in the inhibition of Cbl binding because protease digestion of either bile or bile acid abolishes the Cbl binding ability. Moreover, antibody to R protein abolishes the inhibition. Bile or bile acids do not have a direct effect on either purified IF or the IF-Cbl receptor molecule, even though bile acids increase the attachment of IF-[57Co]Cbl to ileal brush-border membranes. These data demonstrate two steps where components of bile could affect Cbl absorption: the binding of Cbl to IF and of IF-Cbl to its ileal receptor. It is not clear whether these in vitro phenomena are important for the normal absorption of Cbl in vivo.
Intraduodenal emulsions of oleic acid augment acid-induced canine pancreatic secretion
Authors: Fink A. S. , Meyer J. H.
Published: December 2017

To study interactions between intraduodenal acid and emulsified oleic acid, dogs with chronic gastric and pancreatic fistulas received two sets of intestinal perfusates. The first set contained HCl plus bovine serum albumin (BSA) with or without 20 mM oleic acid. The BSA and HCl were varied so that each 50 ml contained 1, 2, or 4 meq of acid titratable from an initial pH of 2.0 or 3.5 to an end-point pH of 4.5. Oleic acid significantly enhanced pancreatic bicarbonate and protein outputs induced by acidified BSA. In additional studies, a less soluble protein solution, a 1:1 mixture of bovine hemoglobin and ovalbumin (HB-OV), was utilized. Fixed amounts of HCl (1, 2, or 4 meq/50 ml) were added to native or pepsin-digested HB-OV solution with or without 20 mM oleic acid. In these studies, initial pH and titratable acid (to end-point pH 4.5) varied with the nature of the HB-OV (undigested or digested), as well as with the amount of HCl added. Under these conditions, digested HB-OV and oleic acid potentiated acid-induced bicarbonate output, but only in those solutions with the greatest amount of added HCl. Acid-induced bicarbonate or protein outputs were not further augmented upon combination of HB-OV digests with oleic acid. We conclude that acid-induced pancreatic bicarbonate secretion is potentiated by intraduodenal protein digests and emulsified fatty acids.
Effect of pancreatic polypeptide on canine migrating motor complex and plasma motilin
Authors: Hall K. E. , Diamant N. E. , El-Sharkawy T. Y. , Greenberg G. R.
Published: December 2017

A potential role of pancreatic polypeptide (PP) in the regulation of phase III of the migrating motor complex (MMC) was investigated in conscious dogs before and during bilateral vagal blockade. After a control fasting period, cyclical increments in plasma PP occurred with peak levels of 45 +/- 8 pmol/l coinciding with late phase II MMC motility. By contrast, after food a substantially higher (approximately five times peak fasting concentrations) and more prolonged elevation of PP was observed, in association with a postprandial pattern of activity. To approximate fasting plasma PP concentrations, porcine PP was infused at 100 pmol X kg-1 X h-1, which produced levels of plasma PP of 99 +/- 8 pmol/l. At this dose PP had no effect on phase III activity. However, at a dose of 400 pmol X kg-1 X h-1, which achieved plasma PP concentrations (283 +/- 33 pmol/l) similar to postprandial levels, there was a specific inhibition of phase III in the lower esophageal sphincter, stomach, duodenum, and upper jejunum. The phase III-associated increment of plasma motilin was also inhibited by this dose of PP. These inhibitory effects at the 400 pmol X kg-1 X h-1 dose of PP were also observed after bilateral blockade of the vagus nerves. Our results suggest that PP has no significant role in the modulation of phase III of the fasting MMC nor does it induce a typical feeding motor pattern. The selective inhibition of both phase III and the associated rise in plasma motilin by PP plasma levels similar to postprandial concentrations does, however, point to a possible role for pancreatic polypeptide in the postprandial inhibition of phase III of the MMC.
Dual effects of electrical stimulation of ventromedial hypothalamic neurons on gastric acid secretion in rats
Authors: Ishikawa T. , Nagata M. , Osumi Y.
Published: December 2017

Effects of electrical stimulation of the ventromedial hypothalamus (VMH) on gastric acid output and mucosal blood flow were examined in rats anesthetized with urethan. With stimulation of this area, a significant increase in acid output and mucosal blood flow occurred in 8 out of 16 animals. In these eight rats, the tip of the electrode had been placed mainly within the caudal portion of VMH. When the basal acid output was maintained at a relatively high level by pretreating the rats with 2-deoxy-D-glucose, electrical stimulation of the VMH significantly reduced the levels of these gastric parameters in 9 out of 12 animals. In the remaining three animals, the tip of the electrode had been placed in an area outside the VMH. These findings suggest that VMH is not a homogeneous neuron group, and both excitatory and inhibitory neurons probably play a role in regulating gastric functions.
Effects of neuronal stimulation on mucosal transport in guinea pig ileum
Authors: Cooke H. J. , Shonnard K. , Wood J. D.
Published: December 2017

The effects of electrical stimulation of enteric nerves on mucosal transport parameters were determined in short-circuited flat sheets of guinea pig ileum. Rectangular bipolar stimulus pulses with a duration of 0.5 ms were applied continuously across Ag-AgCl foil electrodes positioned in parallel with the plane of the tissue. Electrical field stimulation (EFS) elicited a biphasic increase in the short-circuit current (Isc) and transmural electrical potential difference. The response to EFS consisted of an initial rapid rise and decline in Isc followed by a slower rise in Isc to a plateau. This response persisted with some decrement. The maximum change in Isc occurred at stimulus strengths of 3.2-5.2 mA and frequencies of 8-10 Hz. The stimulus-evoked increase in Isc was reversibly abolished by 0.1-0.15 microM tetrodotoxin, 22 mM magnesium, and 0.16 mM cadmium. Prior to EFS, net sodium absorption was 2.3 +/- 0.6 mu eq X cm-2 X h-1 in nine animals, and chloride secretion averaged 1.7 +/- 0.8 mu eq X cm-2 X h-1. EFS had no effect on unidirectional or net sodium fluxes or tissue conductance, whereas it increased active chloride secretion from 1.7 +/- 0.8 to 3.9 +/- 0.6 mu eq X cm-2 X h-1. Tetrodotoxin had no effect on resting sodium or chloride fluxes. These results show that EFS evokes an increase in chloride secretion in guinea pig ileum. These results suggest that EFS alters mucosal transport function by activating enteric neurons.
Antral gland cell column: a method for studying release of gastric hormones
Authors: Richelsen B. , Rehfeld J. F. , Larsson L. I.
Published: December 2017

A technique for studying in vitro release of gastric hormones has been developed. The system utilizes nonenzymatically isolated antropyloric glands from humans or rats, which are perifused in a Bio-Gel P-2 column. The system permits the study of kinetics and dose-response characteristics using the glands as their own control. The glands were stimulated with carbachol and bombesin, and the antral peptides gastrin and somatostatin were measured. Bombesin and carbachol both evoked a dose-dependent stimulation of gastrin release, beginning at below 10(-10) M (bombesin) and 10(-7) M (carbachol). Carbachol inhibited the release of somatostatin in a dose-dependent manner, being maximally effective at 10(-6) M and then producing 60% inhibition of somatostatin release. Bombesin was without effect on antropyloric somatostatin release. These data suggest that the gastrin-stimulating effect of carbachol is partially or totally due to inhibition of somatostatin release, whereas bombesinergic stimulation of gastrin release must work in an independent manner. In addition, data on the effects of these substances on the release of gastrin and ACTH-like peptides from human antropyloric glands are presented. Due to the absence of local neural reflexes, this system is a useful supplement to the isolated perfused stomach model.
Contraction-related, low-frequency components in canine electrogastrographic signals
Authors: van der Schee E. J. , Grashuis J. L.
Published: December 2017

Interdigestive gastric contraction-related phenomena were studied in four healthy conscious dogs by running-spectrum analysis of signals derived from the abdominal surface. When groups of contractions occur irregularly spaced in time, low frequencies (in the range below 0.085 Hz) show up in the power spectra of the electrogastrograms. It has been hypothesized that prolonged electrical control activity (ECA) intervals shown to coincide with irregular contractions are related in some way to these low frequencies. This hypothesis was investigated in detail. Whereas a certain degree of correlation was demonstrated between ECA interval variations, contractile activity, and the presence of low frequencies in the spectra obtained from electrogastrograms recorded during interdigestive migrating complexes, a more pronounced correlation between these phenomena was found during "minute rhythms." It was concluded that the presence of lower frequencies ranging from the normal gastric one to about 0.01 Hz in the running-spectrum representation of electrogastrograms recorded in fasting dogs is indicative of strong antral contractions and that the mechanism through which this is brought about involves prolongation of ECA intervals associated with these contractions.
A transcellular route for Na-coupled Cl transport in secreting pancreatic acinar cells
Authors: O'Doherty J. , Stark R. J.
Published: December 2017

Ion-selective microelectrodes were employed to determine the electrochemical driving forces involved in the transepithelial transport of Na+ and Cl- during acetylcholine (ACh) stimulation of pancreatic acinar cells. In HCO-3-free Ringer solution, the mean values of intracellular Cl and Na activities (aiCl and aiNa) were 68.9 +/- 1.1 and 8.3 +/- 0.3 mM, respectively. The mean value of aiCl is above the calculated equilibrium value, indicating that Cl entry into the cell is an energy-requiring process. Continuous measurement of intracellular electrode potentials during stimulation of the cells with concentrations of ACh ranging from 10(-7) to 10(-5) M demonstrated the neurotransmitter's influence on transmembrane Na+ and Cl- movement in secreting cells. The mean values of the induced changes in aiCl and aiNa at every concentration of ACh measured were not significantly different (P greater than 0.5), although the mean changes in either aiNa or aiCl determined with every decade change in ACh concentration were significant (P less than 0.05). The transmembrane Na+ electrochemical gradient dissipated with the induced increases in aiCl. These results suggest that, during stimulus-secretion coupling of pancreatic acinar cells, there is a transcellular route for NaCl secretion, and the energy for NaCl entry into the cell may be derived from the Na+ electrochemical gradient that exists across the basolateral epithelial membrane. They also suggest that the ACh-induced changes in ionic permeability of the plasma membrane may be the coupling mechanism by which the simultaneous events enzyme release and electrolyte secretion are controlled in stimulated cells.