bluuebunny/crossref_metadata_2025 huggingface dataset:
NHE3-dependent cytoplasmic alkalinization is triggered by Na+-glucose cotransport in intestinal epithelia
Authors: Turner Jerrold R. , Black Eric D.
Published: December 2017

Cytoplasmic pH (pHi) was evaluated during Na+-glucose cotransport in Caco-2 intestinal epithelial cell monolayers. The pHi increased by 0.069 ± 0.002 within 150 s after initiation of Na+-glucose cotransport. This increase occurred in parallel with glucose uptake and required expression of the intestinal Na+-glucose cotransporter SGLT1. S-3226, a preferential inhibitor of Na+/H+ exchanger (NHE) isoform 3 (NHE3), prevented cytoplasmic alkalinization after initiation of Na+-glucose cotransport with an ED50 of 0.35 μM, consistent with inhibition of NHE3, but not NHE1 or NHE2. In contrast, HOE-694, a poor NHE3 inhibitor, failed to significantly inhibit pHi increases at <500 μM. Na+-glucose cotransport was also associated with activation of p38 mitogen-activated protein (MAP) kinase, and the p38 MAP kinase inhibitors PD-169316 and SB-202190 prevented pHi increases by 100 ± 0.1 and 86 ± 0.1%, respectively. Conversely, activation of p38 MAP kinase with anisomycin induced NHE3-dependent cytoplasmic alkalinization in the absence of Na+-glucose cotransport. These data show that NHE3-dependent cytoplasmic alkalinization occurs after initiation of SGLT1-mediated Na+-glucose cotransport and that the mechanism of this NHE3 activation requires p38 MAP kinase activity. This coordinated regulation of glucose (SGLT1) and Na+ (NHE3) absorptive processes may represent a functional activation of absorptive enterocytes by luminal nutrients.
Differential regulation of the expression of Na+/H+ exchanger isoform NHE3 by PKC-α in Caco-2 cells
Authors: Alrefai W. A. , Scaglione-Sewell B. , Tyagi S. , Wartman L. , Brasitus T. A. , Ramaswamy K. , Dudeja P. K.
Published: December 2017

Na+/H+ exchange (NHE) activity has been shown to be regulated by various external signals and protein kinases in many tissues and cell types. A family of six NHE isoforms has been identified. Three isoforms, NHE1, NHE2, and NHE3, have been shown to be expressed in the human intestine. The present studies were designed to study regulation of these human NHE isoforms by the α-isoform of protein kinase C (PKC) in the Caco-2 cell line. The mRNA levels of the NHE isoforms in Caco-2 cells were initially measured by a semiquantitative RT-PCR technique in response to PKC downregulation by long-term exposure to 1 μM 12- O-tetradecanoylphorbol-13-acetate (TPA) for 24 h. PKC downregulation resulted in an ∼60% increase in the mRNA level for NHE3, but not for NHE1 or NHE2. Utilizing dichlorobenzimidazole riboside, an agent to block the synthesis of new mRNA, we demonstrated that the increase in the NHE3 mRNA in response to downregulation of PKC was predominantly due to an increase in the rate of transcription, rather than a decrease in the NHE3 mRNA stability. Consistent with the mRNA results, our data showed that amiloride-sensitive22Na+ uptake was increased after incubation of Caco-2 cells with 1 μM TPA for 24 h. To elucidate the role of PKC-α, an isoform downregulated by TPA, the relative abundance of NHE isoform mRNA levels and the apical NHE activity were assessed in Caco-2 cells over- and underexpressing PKC-α. Our results demonstrated that NHE3, but not NHE1 or NHE2, mRNA was downregulated by PKC-α and that apical NHE activity was higher in cells underexpressing PKC-α and lower in cells overexpressing PKC-α than in control cells. In conclusion, these data demonstrate a differential regulation of NHE3, but not NHE2 or NHE1, expression by PKC in Caco-2 cells, and this regulation appears to be predominantly due to PKC-α.
Effects of IL-8, Gro-α, and LTB4 on the adhesive kinetics of LFA-1 and Mac-1 on human neutrophils
Authors: Seo Scott M. , McIntire Larry V. , Smith C. Wayne
Published: December 2017

Firm adhesion of rolling neutrophils on inflamed endothelium is dependent on β2 (CD18)-integrins and activating stimuli. LFA-1 (CD11a/CD18) appears to be more important than Mac-1 (CD11b/CD18) in neutrophil emigration at inflammatory sites, but little is known of the relative binding characteristics of these two integrins under conditions thought to regulate firm adhesion. The present study examined the effect of chemoattractants on the kinetics of LFA-1 and Mac-1 adhesion in human neutrophils. We found that subnanomolar concentrations of interleukin-8, Gro-α, and leukotriene B4 (LTB4) induced rapid and optimal rates of LFA-1-dependent adhesion of neutrophils to intercellular adhesion molecule (ICAM)-1-coated beads. These optimal rates of LFA-1 adhesion were transient and decayed within 1 min after chemoattractant stimulation. Mac-1 adhesion was equally rapid initially but continued to rise for ≥6 min after stimulation. A fourfold higher density of ICAM-1 on beads markedly increased the rate of binding to LFA-1 but did not change the early and narrow time window for the optimal rate of adhesion. Using well-characterized monoclonal antibodies, we showed that activation of LFA-1 and Mac-1 by Gro-α was completely blocked by anti-CXC chemokine receptor R2, but activation of these integrins by interleukin-8 was most effectively blocked by anti-CXC chemokine receptor R1. The topographical distribution of beads also reflected significant differences between LFA-1 and Mac-1. Beads bound to Mac-1 translocated to the cell uropod within 4 min, but beads bound to LFA-1 remained bound to the lamellipodial regions at the same time. These kinetic and topographical differences may indicate distinct functional contributions of LFA-1 and Mac-1 on neutrophils.
Expression of the reduced folate carrier SLC19A1 in IEC-6 cells results in two distinct transport activities
Authors: Rajgopal Arun , Sierra Esteban E. , Zhao Rongbao , Goldman I. David
Published: December 2017

Intestinal absorption of folates has been characterized as a facilitative process with a low pH optimum. Studies with intestinal epithelial cells have suggested that this activity is mediated by the reduced folate carrier (RFC1). In this paper, we report on folate transport characteristics in an immortalized rat IEC-6 cell line that was found to exhibit the predominant influx activity for methotrexate (MTX) at pH 5.5 with a low level of activity at pH 7.4. Transfection of this cell line with an RFC1 construct resulted in clones exhibiting increased MTX uptake at both the pHs and high folic acid uptake only at the low pH. For the two clones with the highest level of transport activity, relative MTX influx at the two pHs was reversed. Moreover, the low pH MTX influx activity ([MTX]e = 0.5 μM) was markedly inhibited by 20 μM folic acid while influx at neutral pH was not. Furthermore, in the presence and absence of glucose at low pH, MTX and folic acid influx activity was inhibited by azide, while MTX influx at pH 7.4 was stimulated by azide in the absence of glucose but was unchanged in the presence of glucose and azide. This was contrasted with the results of transfection of the same RFC1 construct into an L1210 murine leukemia cell line bearing a nonfunctional endogenous carrier. In this case, the activity expressed was only at pH 7.4. These data indicate that RFC1 can exhibit two distinct types of folate transport activities in intestinal cells that must depend on tissue-specific modulators.
Expression of Ca2+-activated K+channels, SK3, in the interstitial cells of Cajal in the gastrointestinal tract
Authors: Fujita Akikazu , Takeuchi Tadayoshi , Saitoh Noriko , Hanai Jun , Hata Fumiaki
Published: December 2017

A role for small-conductance Ca2+-activated K+ (SK) channels on spontaneous motility of the gastrointestinal tract has been suggested. Although four subtypes of SK channels were identified in mammalian tissues, the subtypes of SK channel expressed in the gastrointestinal tract are still unknown. In this study, we investigated the expression and localization of SK channels in the gastrointestinal tract. RT-PCR analysis shows expression of SK3 and SK4 mRNA, but not SK1 or SK2 mRNA, in the rat intestine. SK3 immunoreactivity was detected in the myenteric plexus and muscular layers of the stomach, ileum, and colon. SK3-immunoreactive cells were stained with antibody for c-kit, a marker for the interstitial cells of Cajal (ICC), but not with that for glial fibrillary acidic protein in the ileum and stomach. Immunoelectron microscopic analysis indicates that SK3 channels are localized on processes of ICC that are located close to the myenteric plexus between the longitudinal and circular muscle layers and within the muscular layers. Because ICC have been identified as pacemaker cells and are known to play a major role in generating the regular motility of the gastrointestinal tract, these results suggest that SK3 channels, which are expressed specifically in ICC, play an important role in generating a rhythmic pacemaker current in the gastrointestinal tract.
Guanine nucleosides and Jurkat cell death: roles of ATP depletion and accumulation of deoxyribonucleotides
Authors: Batiuk Thomas D. , Schnizlein-Bick Carol , Plotkin Zoya , Dagher Pierre C.
Published: December 2017

Guanine nucleosides are toxic to some forms of cancer. This toxicity is pronounced in cancers with upregulated guanine nucleotide synthesis, but the mechanisms are poorly understood. We investigated this toxicity by measuring the effects of guanine nucleosides on nucleotides in Jurkat cells using HPLC. We also measured proliferation and cell death with microscopy and fluorescence-activated cell sorting. Guanosine increased GTP to 600% and reduced ATP to 40% of control. This resulted in cell death with a predominance of necrosis. Deoxyguanosine caused similar increases in GTP but at earlier time points. Cell death was severe with a predominance of apoptosis. Deoxyguanosine but not guanosine increased dGTP to 800% of control. Adenosine inhibited the effects of guanosine, in part by competing for uptake. In stimulated leukocytes, guanosine and deoxyguanosine altered the nucleotide pools in a way qualitatively similar to that observed in Jurkat cells. However, proliferation was enhanced rather than impaired. In conclusion, guanosine and deoxyguanosine are toxic to Jurkat cells through two mechanisms: ATP depletion, causing necrosis, and the accumulation of dGTP, resulting in apoptosis.
Prion protein fragment 106–126 potentiates catecholamine secretion from PC-12 cells
Authors: Taylor S. C. , Green K. N. , Smith I. F. , Peers C.
Published: December 2017

The toxic actions of scrapie prion protein (PrPsc) are poorly understood. We investigated the ability of the toxic PrPsc fragment 106–126 to interfere with evoked catecholamine secretion from PC-12 cells. Prion protein fragment 106–126 (PrP106–126) caused a time- and concentration-dependent augmentation of exocytosis due to the emergence of a Ca2+ influx pathway resistant to Cd2+ but sensitive to other inorganic cations. In control cells, secretion was dependent on Ca2+ influx through L- and N-type Ca2+ channels, but after exposure to PrP106–126, secretion was unaffected by N-type channel blockade. Instead, selective L-type channel blockade was as effective as Cd2+ in suppressing secretion. Patch-clamp recordings revealed no change in total Ca2+ current density in PrP106–126-treated cells or in the contribution to total current of L-type channels, but a small Cd2+-resistant current was found only in PrP106–126-treated cells. Thus PrP106–126 augments secretion by inducing a Cd2+-resistant Ca2+ influx pathway and alters coupling of native Ca2+ channels to exocytosis. These effects are likely contributory factors in the toxic cellular actions of PrPsc.
Growth factors stimulate the Na-K-2Cl cotransporter NKCC1 through a novel Cl−-dependent mechanism
Authors: Jiang Gengru , Klein Janet D. , O'Neill W. Charles
Published: December 2017

The Na-K-2Cl cotransporter NKCC1 is an important volume-regulatory transporter that is regulated by cell volume and intracellular Cl−. This regulation appears to be mediated by phosphorylation of NKCC1, although there is evidence for additional, cytoskeletal regulation via myosin light chain (MLC) kinase. NKCC1 is also activated by growth factors and may contribute to cell hypertrophy, but the mechanism is unknown. In aortic endothelial cells, NKCC1 (measured as bumetanide-sensitive86Rb+ influx) was rapidly stimulated by serum, lysophosphatidic acid, and fibroblast growth factor, with the greatest stimulation by serum. Serum increased bumetanide-sensitive influx significantly more than bumetanide-sensitive efflux (131% vs. 44%), indicating asymmetric stimulation of NKCC1, and produced a 17% increase in cell volume and a 25% increase in Cl− content over 15 min. Stimulation by serum and hypertonic shrinkage were additive, and serum did not increase phosphorylation of NKCC1 or MLC, and did not decrease cellular Cl− content. When cellular Cl− was replaced with methanesulfonate, influx via NKCC1 increased and was no longer stimulated by serum, whereas stimulation by hypertonic shrinkage still occurred. Based on these results, we propose a novel mechanism whereby serum activates NKCC1 by reducing its sensitivity to inhibition by intracellular Cl−. This resetting of the Cl− set point of the transporter enables the cotransporter to produce a hypertrophic volume increase.
GSH depletion, K-Cl cotransport, and regulatory volume decrease in high-K/high-GSH dog red blood cells
Authors: Fujise Hiroshi , Higa Kazunari , Kanemaru Tomomi , Fukuda Miwa , Adragna Norma C. , Lauf Peter K.
Published: December 2017

Thiol reagents activate K-Cl cotransport (K-Cl COT), the Cl-dependent and Na-independent ouabain-resistant K flux, in red blood cells (RBCs) of several species, upon depletion of cellular glutathione (GSH). K-Cl COT is physiologically active in high potassium (HK), high GSH (HG) dog RBCs. In this unique model, we studied whether the same inverse relationship exists between GSH levels and K-Cl COT activity found in other species. The effects of GSH depletion by three different chemical reactions [nitrite (NO2)-mediated oxidation, diazene dicarboxylic acid bis- N, N-dimethylamide (diamide)-induced dithiol formation, and glutathione S-transferase (GST)-catalyzed conjugation of GSH with 1-chloro-2,4-dinitrobenzene (CDNB)] were tested on K-Cl COT and regulatory volume decrease (RVD). After 85% GSH depletion, all three interventions stimulated K-Cl COT half-maximally with the following order of potency: diamide > NO2 > CDNB. Repletion of GSH reversed K-Cl COT stimulation by 50%. Cl-dependent RVD accompanied K-Cl COT activation by NO2 and diamide. K-Cl COT activation at concentration ratios of oxidant/GSH greater than unity was irreversible, suggesting either nitrosothiolation, heterodithiol formation, or GST-mediated dinitrophenylation of protein thiols. The data support the hypothesis that an intact redox system, rather than the absolute GSH levels, protects K-Cl COT activity and cell volume regulation from thiol modification.
Regulation of A-type potassium channels in murine colonic myocytes by phosphatase activity
Authors: Amberg Gregory C. , Koh Sang Don , Perrino Brian A. , Hatton William J. , Sanders Kenton M.
Published: December 2017

A rapidly inactivating K+current (A-type current) participates in the regulation of colonic muscle excitability. We found 19-pS K+ channels in cell-attached patches of murine colonic myocytes that activated and inactivated with kinetics similar to the A-type current. The A-type current in colonic myocytes is regulated by Ca2+/calmodulin-dependent protein kinase II. Therefore, we studied regulation of the 19-pS K+ channels by Ca2+-dependent phosphorylation/dephosphorylation. The rates of inactivation of ensemble-averaged currents resulting from 19-pS K+ channels were increased by the calmodulin antagonist W-7. Inhibitors of calcineurin, cyclosporin A and FK-506, slowed the inactivation of the 19-pS K+ channels. Okadaic acid, an inhibitor of the calcineurin/inhibitor-1/protein phosphatase 1 cascade, also slowed inactivation of the 19-pS K+ channels. Polymerase chain reaction detected transcripts encoding calcineurin A in isolated colonic smooth muscle cells, and immunohistochemical studies demonstrated specific expression of calcineurin A-like immunoreactivity in colonic muscle tissues and in colonic myocytes. These data, when considered with previous findings, suggest that Ca2+-dependent phosphorylation/dephosphorylation regulates the A-type current in murine colonic smooth muscle cells.
Role of microvillar cell surfaces in the regulation of glucose uptake and organization of energy metabolism
Authors: Lange Klaus
Published: December 2017

Experimental evidence suggesting a type of glucose uptake regulation prevailing in resting and differentiated cells was surveyed. This type of regulation is characterized by transport-limited glucose metabolism and depends on segregation of glucose transporters on microvilli of differentiated or resting cells. Earlier studies on glucose transport regulation and a recently presented general concept of influx regulation for ions and metabolic substrates via microvillar structures provide the basic framework for this theory. According to this concept, glucose uptake via transporters on microvilli is regulated by changes in the structural organization of the microfilament bundle, which is acting as a diffusion barrier between the microvillar tip compartment and the cytoplasm. Both microvilli formation and the switch of glucose metabolism from “metabolic regulation” to “transport limitation” occur during differentiation. The formation of microvillar cell surfaces creates the essential preconditions to establish the characteristic functions of specialized tissue cells including the coordination between glycolysis and oxidative phosphorylation, regulation of cellular functions by external signals, and Ca2+ signaling. The proposed concept integrates various aspects of glucose uptake regulation into a ubiquitous cellular mechanism involved in regulation of transmembrane ion and substrate fluxes.
Characterization of RIIβ and D-AKAP1 in differentiated adipocytes
Authors: Chaudhry Archana , Zhang Chen , Granneman James G.
Published: December 2017

A-kinase anchoring proteins (AKAPs) have been proposed to regulate cAMP-dependent signaling in the cell by targeting RII subunits of protein kinase A (PKA) to specific subcellular compartments. RIIβ is the predominant PKA subtype in adipose tissue. In gel overlay assays of C3H/10T1/2 adipocytes and adipose tissue, RIIβ bound to several proteins including a prominent 132-kDa band, which was strongly induced upon differentiation of C3H/10T1/2 cells into adipocytes. Immunoblotting and nuclease protection analysis of C3H/10T1/2 cellular extracts identified this band as D-AKAP1/S-AKAP84, a putative AKAP. Immunocytochemical analysis of C3H/10T1/2 adipocytes revealed that most of D-AKAP1/S-AKAP84, but not RIIβ, was colocalized with a mitochondrial-selective dye, MitoTracker red. These findings were further confirmed in studies where D-AKAP1/ S-AKAP84, but not RIIβ, were localized in purified mitochondria made from C3H/10T1/2 adipocytes. Moreover, D-AKAP1, which is upregulated after differentiation, did not recruit RIIβto membrane fractions enriched in mitochondria. These results demonstrate that D-AKAP1/S-AKAP84 does not interact with PKA in differentiated C3H/10T1/2 adipocytes under the conditions tested.
Expression, regulation, and function of P2X4purinergic receptor in human cervical epithelial cells
Authors: Gorodeski George I.
Published: December 2017

Micromolar concentrations of ATP stimulate biphasic change in transepithelial conductance across CaSki cultures on filters, an acute transient increase ( phase I response; triggered by P2Y2receptor and mediated by calcium mobilization-dependent cell volume decrease) followed by a slower decrease in permeability ( phase II response). Phase II response is mediated by augmented calcium influx and protein kinase C-dependent increase in tight junctional resistance. The objective of the study was to determine the role of P2X4 receptor as a mediator of phase II response. Human cervical epithelial cells express P2X4 receptor mRNA (1.4-, 2.2-, and 4.4-kb isoforms by Northern blot analysis) and P2X4 protein. Depletion of vitamin A reversibly downregulated P2X4 receptor mRNA and protein and ATP-induced calcium influx. Depletion of vitamin A abrogated phase II response, and the effect could be partially reversed only with retinoic acid receptor (RAR)-selective retinoids but not retinoid X receptor (RXR) agonists. Depletion of vitamin A also abrogated protein kinase C increase in tight junctional resistance, and the effect could not be reversed with retinoids. Depletion of vitamin A also abrogated phase I increase in permeability and reversibly downregulated P2Y2 receptor mRNA and ATP-induced calcium mobilization. However, in contrast to phase II response, both RAR and RXR agonists could fully reverse those effects. These results suggest that phase IIresponse is mediated by a P2X4 receptor mechanism.
Glucose load diverts hepatic gluconeogenic product from glucose to glycogen in vivo.
Authors: Shikama H , Ui M
Published: December 2017

Intravenous or oral administration of concentrated glucose solution into fasted rats simultaneously injected with 14C-bicarbonate resulted in an inhibition of [14C]glucose release into the blood and in an accelerated [14C]glycogen formation associated with glycogen synthetase activation and phosphorylase inactivation in the liver. The specific activity of glycogen was much higher than that of blood glucose after the glucose load, indicating that glycogen originated from gluconeogenesis rather than blood glucose. These metabolic changes induced by the glucose load were not mediated by endogenous insulin because they were observed to the same extent in rats treated with anti-insulin serum. However, they were mostly, if not totally, abolished by adrenalectomy, which suppressed gluconeogenesis and glycogenesis. Glucose tolerance was markedly impaired not only by anti-insulin serum, which inhibits peripheral glucose utilization, but also by adrenalectomy, which affects hepatic metabolism. It is concluded that a glucose load diverts the final product of hepatic gluconeogenesis from blood glucose to liver glycogen; these metabolic changes in the liver are an important determinant of glucose tolerance.
Applied pressures and net water flux across in vitro frog gastric mucosa.
Authors: Villegas L
Published: December 2017

The effects of hydrostatic pressure differences up to 0.4 atm/413 cmH2O were studied on frog gastric mucosa in vitro. Net water flux, transmucosal electrical potential difference, and acid secretion were measured. A significant correlation between hydrostatistic pressure difference and net water flow (r=0.77) was obtained. The intercept of the regression line, at zero hydrostatic pressure difference, is 9.3 +/- 0.5 microliter/cm2.h, and the slope 42.9 +/- 3.2 microliter/cm2.atm.h. No significant correlation was obtained between the hydrostatic pressure difference and the transmucosal potential difference (P greater than 0.20), the acid secretion (P greater than 0.20), or the nonacidic chloride transport, measured as short-circuit current (P greater than 0.20). Hydrostatic water flux is compared to osmotically induced flux previously reported. It is proposed that the difference between hydrostatic and osmotic induced water fluxes is due to the area of cells exposed to the pressures. Only part of surface cells are directly exposed to the osmotic pressure due to the presence of restricted extracellular compartments.
Smooth muscle mechanical responses in vitro to bethanechol after progesterone in male rat.
Authors: Bruce L A , Behsudi F M , Danhof I E
Published: December 2017

Male Sprague-Dawley rats were pretreated subcutaneously with either progesterone (3 mg/kg per day) in a vehicle or a vehicle only for 3 days. Antral and gastroduodenal junctional tissues (GJT) were excised from both groups of animals and prepared for in vitro mechanical measurements. Responses from the circular muscle axis of these tissues were recorded with strain gauge transducers over a 30-min period. Chemical stimulation of the tissue was achieved with a muscarinic agonist, bethanechol chloride. Log-dose response curves suggested that untreated antral tissue generated stronger contractile activity than untreated GJT on an equal weight basis at bethanechol dose levels of 6.4 X 10(-6) M to 1 X 10(-4) M (P less than 0.005). Antral tissue and GJT contractile activity from the progesterone pretreated animals was significantly reduced (P less than 0.01) compared to the corresponding tissues from untreated animals at bethanechol dose levels of 6.4 X 10(-6) M and 1.28 X 10(-5) M. Progesterone pretreatment appeared to have little effect on the contractile frequency of either tissue. These results suggest possible progesteronic influences on contractile force in gastrointestinal smooth muscle.
Effects of solute-coupled transport on lymph flow and oncotic pressures in cat ileum.
Authors: Granger D N , Taylor A E
Published: December 2017

The effects of net volume absorption rate on steady-state lymphatic and capillary volume flows, lymphatic protein flux, and lymph oncotic pressure were analyzed in an isolated vascularly perfused cat ileum preparation. Solute-coupled fluid transport was stimulated by instilling either Tyrode solution, Tyrode + glucose, Tyrode + taurocholic acid (TC), Tyrode + TC + oleic acid, or Tyrode + aspartic acid, into the ileal lumen. Lymph flow increased in a sigmoidal fashion as net volume absorption rate increased. A linear relationship was observed between lymphatic protein flux and net volume absorption rate. The relative contributions of the intestinal capillary and lymphatic systems in removing absorbed volume from the mucosal interstitium was highly dependent on the rate of net volume absorption. Lymph oncotic pressure decreased progressively as net volume absorption rate increased with a maximal reduction in lymph oncotic pressure of 6.0-7.0 mmHg at the higher volume absorption rates. The results of this study indicate that 1) the rate of solute-coupled fluid transport greatly influences the rate of intestinal lympathic and capillary volume flows, lymphatic protein flux, and lymph oncotic pressure, 2) a reduction in tissue oncotic pressure may serve as the major driving force for vascular removal of absorved volume, and 3) the increase in capillary permeability to plasma proteins during fluid transport is related to the rate of volume absorption.
Role of thyroid gland in oxygen toxicity.
Authors: Galton V A
Published: December 2017

The effects of hyperoxia at ambient pressure on thyroid function and thyroid hormone metabolism have been assessed. Thyroidal activity was depressed in mice and rats by exposure to hyperoxia, due at least in part to a decrease in the rate of secretion of pituitary thyrotropin. The effects of hyperoxia on the peripheral deiodination of thyroxine (T4) were dependent on the concentration of oxygen employed and/or the duration of exposure; exposure to 40--80% oxygen for 96 h resulted in decreases in the rate of deiodination and in the deiodinative clearance of [125I]T4. Hyperoxia also resulted in a marked fall in the serum concentration of endogenous T4 and a decrease in T4-binding activity in serum. Many of these effects of hyperoxia were prevented by the concomitanat administration of large amounts of vitamin E (alpha-tocopherol acetate). These decreases in thyroid function and T4 metabolism were associated with a decrease in the rate of whole body oxygen consumption. Thus, the deleterious effects of oxygen in the rat were not due, even in part, to an oxygen-induced hyperthyroid state in the peripheral tissues.
beta-carotene intestinal absorption: bile, fatty acid, pH, and flow rate effects on transport.
Authors: Hollander D , Ruble P E
Published: December 2017

beta carotene absorption in the unanesthetized rat was investigated by recirculating a micellar perfusate that contained beta-carotene through jejunal and ileal intestinal loops. Radioautography revealed extensive distribution of the provitamin throughout the layers of the small bowel. A linear relationship was found between the concentration of beta-carotene in the perfusate and its rate of absorption at perfusate concentrations of 0.5--11 mM. Increases in the perfusate hydrogen ion concentrations, additions of fatty acids of varied chain lengths and degrees of saturation, and an increase in the perfusate flow rate caused higher rates of beta-carotene absorption. Increase in the perfusate sodium taurocholate concentration above 2.5 microM did not change the absorption rate of beta-carotene. These experiments indicate that beta-carotene absorption takes place by passive diffusion. The process of diffusion can be modulated by intraluminal factors that change the physical characteristics of perfusate or stimulate the intracellular cleavage of carotene to retinal.
Galactose metabolism in isolated perfused suckling-rat liver.
Authors: Berman W , Rogers S , Bautista J , Segal S
Published: December 2017

The metabolic conversion of 1, 2, or 4 mM galactose to glucose was studied in isolated livers of suckling rats. Whereas galactose uptake during perfusion with 1 and 2 mM galactose was linear throughout the 90-min experiment, uptake was delayed for 35 min when 4 mM galactose was perfused. Studies with radioactive galactose revealed a parallel disappearance of galactose and the appearance of [14C]glucose; about 80% of the galactose taken up was converted to glucose. Galactose perfusion appeared to reduce the basal amount of glucose derived from substrates other than galactose. The specific activities in the galactose-perfused livers of the three major galactose metabolizing enzymes, galactokinase, galactose-1-phosphate uridylyltransferase, and uridine diphosphogalactose-4-epimerase, revealed that the transferase was significantly lower, whereas that of galactokinase and epimerase were significantly higher than in livers perfused without galactose. No meaningful changes were observed in the levels of either phosphorylated or uridylated hexoses in these studies.
Secretion of an insulinotropic factor from isolated, perfused rat intestine.
Authors: Levin S R , Pehlevanian M Z , Lavee A E , Adachi R I
Published: December 2017

To examine gut-islet interrelationships, we entirely separated the gastrointestinal tract from the rat. When we arterially perfused this preparation with an erythrocyte-free solution for 1 h, it remained histologically intact and took up oxygen and glucose. Feedings were given via a duodenal tube. The gut absorbed glucose when glucose in the feeding was high (9.2 g/dl), but not when glucose in the feeding was low (58 mg/dl). With feeding, the portal venous effluent (PVE) from this preparation (stomach to ileum) enhanced late-phase, glucose-induced insulin secretion from pancreas of another rat. This enhancement occurred when the gut was fed either glucose (9.2 g/dl) in electrolyte solution or electrolyte solution alone. PVE from glucose-fed upper gut (stomach, duodenum) was similarly insulinotropic. In contrast, PVE from unfed gut or from glucose-fed gut of old rats was not insulinotropic. PVE from all gut preparations except upper gut produced a glucagon "spike" during basal pancreatic perfusion. Effects of gastrointestinal peptides (gastric inhibitory polypeptide, cholecystokinin octapeptide, secretin, gastrin) and immunoassays of PVE suggested that the insulinotropic substance is not one of these peptides. Thus, an insulinotropic substance that is not dependent on feeding nutrient material is secreted from the intestine.
Effect of age on intestinal calcium absorption and adaptation to dietary calcium.
Authors: Armbrecht H J , Zenser T V , Bruns M E , Davis B B
Published: December 2017

To study the reported decline in intestinal calcium absorption with age, calcium active transport, immunoreactive calcium protein (CaBP) content, and alkaline phosphatase activity were measured in the intestine of two strains of rats aged 3-wk--20 mo. Calcium active transport, as measured by everted gut sacs from Sprague-Dawley rats, was greatest at 3 wk, but it declined rapidly with no active transport demonstrable at 3 mo or thereafter. CaBP content closely paralleled the decline in active transport, but alkaline phosphatase activity increased as active transport decreased. Intestinal adaptation to dietary calcium was studied by feeding high- and low-calcium diets to Fischer 344 rats aged 1.5--12 mo. In 1.5-mo-old rats fed a low-calcium diet, there was an increase in calcium active transport, CaBP content, and alkaline phosphatase activity relative to animals fed a high-calcium diet. However, the magnitude of this intestinal adaptation decreased with age until there was only marginal adaptation by 12 mo. The observed changes in calcium active transport with age and diet may be explained by the parallel changes in the vitamin D-dependent CaBP content of the intestine.
Regulation of insulin secretion by phospholipase C
Authors: Zawalich W. S. , Zawalich K. C.
Published: December 2017

Biphasic insulin secretion in response to a sustained glucose stimulus occurs when rat or human islets are exposed to high levels of the hexose. A transient burst of hormone secretion is followed by a rising and sustained secretory response that, in the perfused rat pancreas, is 25- to 75-fold greater than prestimulatory insulin release rates. This insulin secretory response is paralleled by a significant five- to sixfold increase in the phospholipase C (PLC)-mediated hydrolysis of islet phosphoinositide (PI) pools by high glucose. In contrast, mouse islets, when stimulated under comparable conditions with high glucose, display a second-phase response that is flat and only slightly (two- to threefold) greater than prestimulatory release rates. The minimal second-phase insulin secretory response to high glucose is accompanied by the minimal activation of PLC in mouse islets as well. However, stimulation of mouse islets with the protein kinase C (PKC) activator tetradecanoyl phorbol acetate (TPA) or the muscarinic agonist carbachol, which significantly activates an isozyme of PLC distinct from that activated by high glucose, induces a rising and sustained second-phase insulin secretory response. When previously exposed to high glucose, both rat and human islets respond to subsequent restimulation with an amplified insulin secretory response. They display priming, sensitization, or time-dependent potentiation. In contrast, mouse islets primed under similar conditions with high glucose fail to display this amplified insulin secretory response on restimulation. Mouse islets can, however, be primed by brief exposure to either TPA or carbachol. Finally, whereas rat islets are desensitized by chronic exposure to high glucose, mouse islet insulin secretory responses are relatively immune to this adverse effect of the hexose. These and other findings are discussed in relationship to the role being played by agonist-induced increases in the PLC-mediated hydrolysis of islet phosphoinositide pools and the activation of PKC in these species-specific insulin secretory response patterns.
Influence of substance P on myoelectric activity of the small bowel
Authors: Thor P. J. , Sendur R. , Konturek S. J.
Published: December 2017

The effects of substance P (SP) on intestinal myoelectric activity were examined in conscious dogs with implanted silver electrodes on the small doses (0.25-1.0 nmol . kg-1 . h-1) raised the frequency of interdigestive myoelectric complexes and also increased preburst activity, mostly in the upper small bowel. The ileum was relatively less sensitive to the stimulatory action of sp. At higher doses (2.04.0 nmol . kg-1 . h-1) SP caused a fedlike motility pattern. In the doses used SP did not change the foodinduced motility pattern. The effects of SP on myoelectric activity were blocked by atropine or pirenzepine. We conclude that SP was participate in neurally mediated changes in intestinal motility.
Modeling the effect of wall movement on absorption in the intestine
Authors: Macagno E. O. , Christensen J. , Lee C. L.
Published: December 2017

Intestinal wall movements may influence intestinal absorption by inducing flow in the luminal volume. Direct evidence for this is scant and weak. Such evidence was sought by mechanical and analytical modeling. Wall motions resembling peristaltic ring contractions were induced in dialysis tubing filled with a concentrated salt solution and immersed in tap water. The disappearance of solute from the inside of the tube was monitored with conductivity probes and correlated with various kinds of wall motions. In analytical modeling, equations representing wall motions, flow, and mass transfer were constructed, with the assumptions that ring contractions are axisymmetric, the wall is totally compliant, the Reynolds' number is low, the fluid volume is conserved, the no-slip condition exists at the luminal surface, and inertial flow is negligible. In the mechanical model, wall motions caused a 30-35% increase in absorption that was matched in the corresponding analytical model. The analytical model demonstrated that the effect is progressively greater for nonpropagative stationary contractions, asymmetric progressive contractions, and symmetric progressive contractions, the increase being 33, 70, and 100%, respectively.
Enterocyte alpha 2-adrenergic receptors: yohimbine and p-aminoclonidine binding relative to ion transport
Authors: Chang E. B. , Field M. , Miller R. J.
Published: December 2017

We previously reported that alpha 2-adrenergic agonists enhance absorption and inhibit secretion of electrolytes in small intestine. The present study was undertaken to characterize and localize the relevant receptors. Plasma membranes derived from isolated rabbit ileal epithelial cells were incubated with either [3H]yohimbine (Yo), an alpha 2-antagonist, or p-[3H]aminoclonidine (PAC), an alpha 2-agonist. Scatchard analysis of [3H]Yo binding suggests a single receptor. Competitive displacement of Yo from this receptor by other ligands had a potency order characteristic for alpha 2-receptors in other tissue systems. A Scatchard plot of [3H]PAC binding was curvilinear and best fit by assuming two independent site. Competitive displacement of [3H]PAC by PAC in the presence of 140 mM Na+ or 0.1 mM GTP increased the IC50 for PAC binding from 10 nM to 100 and 105 nM, respectively, and the Hill coefficient from 0.7 to 1.2 and 1.0, respectively. The ED50 for PAC effect on short-circuit current (200 nM) does not differ significantly from these values. We conclude that alpha 2-receptors are present on ileal enterocytes and that these receptors mediate enterocyte fluid and electrolyte transport function.
Role of inorganic electrolytes in bile acid-independent canalicular bile formation
Authors: Anwer M. S. , Hegner D.
Published: December 2017

Ion-replacement studies were carried out in the isolated perfused rat liver to obtain insight into the role played by inorganic electrolytes in bile acid-independent canalicular bile flow (BAICF). The BAICF decreased significantly when Na+ (146 mM) was replaced by 120 mM K+, Rb+, Cs+, or choline and when Cl- (127 mM) was replaced by 120 mM acetate or isethionate; there was no reduction in BAICF when Na+ was replaced by Li+ (146 mM) and Cl- by NO-3. K+, Rb+, and Cs+, however, also caused a simultaneous decline in the perfusion rate. The BAICF decreased by 50% when HCO-3 was replaced by equimolar tricine; under this condition replacement of Cl- by NO-3, but not Na+ by Li+, decreased BAICF by 45%. Thus the hepatic transport of Cl- cannot be explained by simple diffusion only, and a special mechanism, probably Na+-coupled Cl- transport, may contribute about 30% of the BAICF. With Li+ replacing Na+ in the medium, the intracellular concentration of Li+ in isolated rat hepatocytes was less than that calculated for electrochemical equilibrium and was increased by 2 mM KCN, indicating active extrusion of this ion. Li+ was unable to activate Mg2+-ATPase of isolated rat liver plasma membranes, and 1 mM ouabain did not affect the Li+ distribution. These results suggest the potential importance of ion pumps other than Na+-K+-ATPase in BAICF.
Kinetics of zinc absorption by the rat jejunum: effects of adrenalectomy and dexamethasone
Authors: Bonewitz R. F. , Foulkes E. C. , O'Flaherty E. J. , Hertzberg V. S.
Published: December 2017

Effects of dexamethasone and adrenalectomy on the kinetics of jejunal 65Zn uptake and absorption were studied in the anesthetized adult rat. The jejunal lumen was perfused in situ with 5 mM glucose in 150 mM saline containing 65Zn and [14C]polyethylene glycol as volume marker. Over the 30-min perfusion period, the rate of net 65Zn removal from the perfusate was biexponential due to the establishment of a return flux to the lumen. An open two-compartment model satisfactorily describes these observations: (formula; see text) Dexamethasone (2 mg/kg ip 7 h before perfusion) increased k12 by 75% (P less than 0.0002) and decreased k20 by 45% (P less than 0.04). Both effects were independent of adrenalectomy. Mathematical simulations using the compartmental model and experimentally determined kinetic constants predicted that transfer of 65Zn into the body should be enhanced by adrenalectomy and retarded by dexamethasone administered to adrenalectomized rats. Dexamethasone and adrenalectomy thus differentially affect Zn uptake and absorption in this system, suggesting a possible adrenocortical hormone involvement in the regulation of Zn absorption. These changes are apparently not mediated via metallothionein.
Ontogeny of cell proliferation and DNA synthesis in rat colon: role of glucocorticoids
Authors: Buts J. P. , De Meyer R. , Kolanowski J.
Published: December 2017

This study was undertaken to determine whether the rat colon exhibits ontogenic changes in epithelial cell proliferation and DNA synthesis during growth. DNA synthesis was measured at intervals after birth in four colonic segments by the incorporation rates of [3H]thymidine. The labeled crypt cell index was determined by radioautography. New findings from our study are that 1) in each colonic segment of suckling rats, [3H]thymidine incorporation rate overshot the adult levels (49-119%) with a peak occurring at day 14 postpartum, 2) between days 14 and 20, the incorporation rates declined sharply to adult values and remained thereafter unchanged until adulthood; during the same period, the labeled and mitotic index decreased, respectively, from 52 to 19% and from 3.58 to 1.43%, 3) the decrease in DNA synthesis and in cell proliferation rates was concomitant with an upsurge in plasma total corticosterone initiated on day 14, and 4) treatment of 10-day-old sucklings with physiological doses of hydrocortisone for 4 consecutive days significantly depressed (P less than 0.01) colonic DNA content and DNA synthesis rates to levels about 45-67% of the control values. These data indicate that growth of the colon may be under the control of glucocorticoid secretion at the weaning period.
Biological activity of canine intestinal cholecystokinin-58
Authors: Eysselein V. E. , Deveney C. W. , Sankaran H. , Reeve J. R. , Walsh J. H.
Published: December 2017

The biological activity of a recently characterized cholecystokinin molecule, canine CCK-58, has been tested using perifused canine gallbladder strips and isolated mouse pancreatic acini. It has been shown that canine CCK-58, purified by affinity chromatography and molecular sieve chromatography, is biologically as potent as canine CCK-39,33 (component II) and synthetic CCK-8. The biological responses were inhibited by dibutyryl cGMP, a known CCK antagonist. CCK-58 is one of the main large molecular forms of CCK in the intestine mucosa. Whether CCK-58 is only an intracellular precursor of other CCK molecules or an important circulating hormone cannot be determined from the data currently available.
Prostaglandins and alkaline secretion from oxyntic, antral, and duodenal mucosa of the dog
Authors: Konturek S. J. , Tasler J. , Bilski J. , Kania J.
Published: December 2017

Alkaline secretion (AS) measured under basal conditions in oxyntic and antral pouches of conscious dogs averaged about 20 mumol/30 min and was about three times lower than that from the duodenal pouch. Natural prostaglandin E2 and prostaglandin F2 alpha, but not prostaglandin I2, were effective stimulants of AS, mainly when given topically. Stable analogues such as 16,16-dimethyl prostaglandin E2 and prostaglandin I2 were relatively more potent stimulants than their parent prostaglandins (PGs), particularly when applied topically. The highest alkaline response of the oxyntic pouch to PG was about 5% of the maximal acid response of this pouch to histamine. Indomethacin reduced markedly AS from the duodenal but not from the oxyntic or antral pouch. AS from the duodenal pouch was relatively more sensitive than that from gastric pouches to the stimulation by PGs, which were effective also after pretreatment with indomethacin. This study shows that the oxyntic, antral, and duodenal mucosa of conscious dogs is capable of secreting bicarbonate, and this secretion, particularly from the duodenal mucosa, is highly sensitive to the stimulation with certain PGs, mainly of the E and F type and their analogues, and to suppression by indomethacin, a potent inhibitor of PG biosynthesis, suggesting that endogenous PGs are involved in the mechanism of AS.
Role of the hepatic branch of the vagus nerve in liver regeneration in rats
Authors: Tanaka K. , Ohkawa S. , Nishino T. , Niijima A. , Inoue S.
Published: December 2017

The role of the vagus nerve in liver regeneration after partial hepatectomy was examined by comparing the effects of hepatic vagotomy (sectioning of the hepatic branch of the vagus nerve) with those of subdiaphragmatic vagotomy in rats. Hepatic vagotomy delayed but did not suppress the increase in the rate of hepatic DNA synthesis and the activity of thymidine kinase after partial hepatectomy. On the other hand, subdiaphragmatic vagotomy delayed and suppressed these indices. The time courses of restoration of liver DNA content after partial hepatectomy were not affected by hepatic vagotomy. However, this index was both delayed and suppressed in subdiaphragmatic vagotomized rats. Hepatic vagotomy did not affect the daily food intake or the body weight increase after partial hepatectomy. However, subdiaphragmatic vagotomy caused considerably more loss of food intake and body weight. There were no differences in the plasma insulin levels after partial hepatectomy among three groups. We concluded that a vagal specific effect is evident in the delay but fails to suppress liver regeneration.
Taurodeoxycholate and the developing rabbit distal colon: absence of secretory effect
Authors: Potter G. D. , Lester R. , Burlingame S. M. , Mitchell P. A. , Schmidt K. L.
Published: December 2017

Failure to absorb bile acids by the ileum leads to fluid secretion by the colon and diarrhea in adults. The infant ileum, however, does not actively transport bile acids. Therefore, we investigated the effect of taurodeoxycholic acid (TDCA) on ion transport in the colon of rabbits 7-10 days old. We mounted distal colon from infant and adult rabbits in modified Ussing chambers and exposed the mucosal or serosal surfaces to TDCA. In the adult, 50 microM TDCA produced an increase in short-circuit current (delta Isc = 1.0 +/- 0.3 mu eq . h-1 . cm-2, P less than 0.05) and Cl secretion. In the infant, the effect was different, Isc was reduced (delta Isc = -1.1 +/- 0.2 mu eq . h-1 . cm-2, P less than 0.01) and ion flux was not altered. Microscopy demonstrated that the infant epithelium was not significantly damaged by exposure to TDCA at these concentrations. The infant colon was, however, capable of a secretory response to a variety of agonists including theophylline, carbachol, bradykinin, serotonin, and 12,13-dibutyryl phorbol ester. The infant rabbit distal colon lacks a secretory response to TDCA during that period when the ileum cannot transport bile acids.