bluuebunny/crossref_metadata_2025 huggingface dataset:
Airway surface fluid volume and Cl content in cystic fibrosis and normal bronchial xenografts
Authors: Zhang Yulong , Engelhardt John F.
Published: December 2017

We describe the use of an in vivo human bronchial xenograft model of cystic fibrosis (CF) and non-CF airways to investigate pathophysiological alterations in airway surface fluid (ASF) volume (Vs) and Cl content. Vs was calculated based on the dilution of an impermeable marker, [3H]inulin, during harvesting of ASF from xenografts with an isosmotic Cl-free solution. These calculations demonstrated that Vs in CF xenographs (28 ± 3.0 μl/cm2; n = 17) was significantly less than that of non-CF xenografts (35 ± 2.4 μl/cm2; n = 30). The Cl concentration of ASF ([Cl]s) was determined using a solid-state AgCl electrode and adjusted for dilution during harvesting using the impermeable [3H]inulin marker. Cumulative results demonstrate small but significant elevations ( P < 0.045) in [Cl]s in CF (125 ± 4 mM; n = 27) compared with non-CF (114 ± 4 mM; n = 48) xenografts. To investigate potential mechanisms by which CF airways may facilitate a higher level of fluid absorption yet retain slightly elevated levels of Cl, we sought to evaluate the capacity of CF and non-CF airways to absorb both 22Na and36Cl. Two consistent findings were evident from these studies. First, in both CF and non-CF xenografts,22Na and36Cl were always absorbed in an equal molar ratio. Second, CF xenografts hyperabsorbed (∼1.5-fold higher) both 22Na and36Cl compared with non-CF xenografts. These results substantiate previously documented findings of elevated Na absorption in CF airways and also suggest that the slightly elevated [Cl]s found in this study of CF xenograft epithelia does not occur through a mechanism of decreased apical permeability to Cl.
Genetic and biochemical determinants of abnormal monovalent ion transport in primary hypertension
Authors: Orlov Sergei N. , Adragna Norma C. , Adarichev Viacheslav A. , Hamet Pavel
Published: December 2017

Data obtained during the last two decades show that spontaneously hypertensive rats, an acceptable experimental model of primary human hypertension, possess increased activity of both ubiquitous and renal cell-specific isoforms of the Na+/H+exchanger (NHE) and Na+-K+-2Cl−cotransporter. Abnormalities of these ion transporters have been found in patients suffering from essential hypertension. Recent genetic studies demonstrate that genes encoding the β- and γ-subunits of ENaC, a renal cell-specific isoform of the Na+-K+-2Cl−cotransporter, and α3-, α1-, and β2-subunits of the Na+-K+pump are localized within quantitative trait loci (QTL) for elevated blood pressure as well as for enhanced heart-to-body weight ratio, proteinuria, phosphate excretion, and stroke latency. On the basis of the homology of genome maps, several other genes encoding these transporters, as well as the Na+/H+exchanger and Na+-K+-2Cl−cotransporter, can be predicted in QTL related to the pathogenesis of hypertension. However, despite their location within QTL, analysis of cDNA structure did not reveal any mutation in the coding region of the above-listed transporters in primary hypertension, with the exception of G276L substitution in the α1-Na+-K+pump from Dahl salt-sensitive rats and a higher occurrence of T594M mutation of β-ENaC in the black population with essential hypertension. These results suggest that, in contrast to Mendelian forms of hypertension, the altered activity of monovalent ion transporters in primary hypertension is caused by abnormalities of systems involved in the regulation of their expression and/or function. Further analysis of QTL in F2hybrids of normotensive and hypertensive rats and in affected sibling pairs will allow mapping of genes causing abnormalities of these regulatory pathways.
Chemical signaling from colonic smooth muscle cells to DRG neurons in culture
Authors: Ennes H. S. , Young S. H. , Goliger J. A. , Mayer E. A.
Published: December 2017

Transduction mechanisms between target cells within the intestinal wall and peripheral terminals of extrinsic primary afferent neurons are poorly understood. The purpose of this study was to characterize the interactions between smooth muscle cells from the rat distal colon and lumbar dorsal root ganglion (DRG) neurons in coculture. DRG neurons visually appeared to make contact with several myocytes. We show that brief mechanical stimulation of these myocytes resulted in intracellular Ca2+ concentration ([Ca2+]i) transients that propagated into 57% of the contacting neurites. Direct mechanical stimulation of DRG neurites cultured without smooth muscle had no effect. We also show that colonic smooth muscle cells express multiple connexin mRNAs and that these connexins formed functional gap junctions, as evidenced by the intercellular transfer of Lucifer yellow. Furthermore, thapsigargin pretreatment and neuronal heparin injection abolished the increase in neurite [Ca2+]i, indicating that the neuronal Ca2+signal was triggered by inositol 1,4,5-trisphosphate-mediated Ca2+ release from intracellular stores. Our results provide evidence for intercellular chemical communication between DRG neurites and intestinal smooth muscle cells that mediates the exchange of second messenger molecules between different cell types.
Fiber type populations and Ca2+-activation properties of single fibers in soleus muscles from SHR and WKY rats
Authors: Bortolotto Susan K. , Stephenson D. George , Stephenson Gabriela M. M.
Published: December 2017

Electrophoretic analyses of muscle proteins in whole muscle homogenates and single muscle fiber segments were used to examine myosin heavy chain (MHC) and myosin light chain 2 (MLC2) isoform composition and fiber type populations in soleus muscles from spontaneously hypertensive rats (SHRs) and their age-matched normotensive controls [Wistar-Kyoto (WKY) rats], at three stages in the development of high blood pressure (4 wk, 16 wk, and 24 wk of age). Demembranated (chemically skinned with 2% Triton X-100), single fiber preparations were used to determine the maximum Ca2+-activated force per cross-sectional area, calcium sensitivity, and degree of cooperativity of the contractile apparatus and Ca2+-regulatory system with respect to Ca2+. The results show that, at all ages examined, 1) SHR soleus contained a lower proportion of MHCI and MLC2 slow (MLC2s) and a higher proportion of MHCIIa, MHCIId/x, and MLC2 fast (MLC2f ) isoforms than the age-matched controls; 2) random dissection of single fibers from SHR and WKY soleus produced four populations of fibers: type I (expressing MHCI), type IIA (expressing MHCIIa), hybrid type I+IIA (coexpressing MHCI and MHCIIa), and hybrid type IIA+IID (coexpressing MHCIIa and MHCIId/x); and 3) single fiber dissection from SHR soleus yielded a lower proportion of type I fibers, a higher proportion of fast-twitch fibers (types IIA and IIA+IID), and a higher proportion of hybrid fibers (types I+IIA and IIA+IID) than the homologous muscles from the age-matched WKY rats. Because the presence of hybrid fibers is viewed as a marker of muscle transformation, these data suggest that SHR soleus undergoes transformation well into adulthood. Our data show also that, for a given fiber type, there are no significant differences between SHR and WKY soleus muscles with respect to any of the Ca2+-activation properties examined. This finding indicates that the lower specific tensions reported in the literature for SHR soleus muscles are not due to strain- or hypertension-related differences in the function of the contractile apparatus or regulatory system.
A3 adenosine receptors regulate Cl−channels of nonpigmented ciliary epithelial cells
Authors: Mitchell Claire H. , Peterson-Yantorno Kim , Carré David A. , McGlinn Alice M. , Coca-Prados Miguel , Stone Richard A. , Civan Mortimer M.
Published: December 2017

Adenosine stimulates Cl− channels of the nonpigmented (NPE) cells of the ciliary epithelium. We sought to identify the specific adenosine receptors mediating this action. Cl− channel activity in immortalized human (HCE) NPE cells was determined by monitoring cell volume in isotonic suspensions with the cationic ionophore gramicidin present. The A3-selective agonist N 6-(3-iodobenzyl)-adenosine-5′- N-methyluronamide (IB-MECA) triggered shrinkage (apparent K d = 55 ± 10 nM). A3-selective antagonists blocked IB-MECA-triggered shrinkage, and A3-antagonists (MRS-1097, MRS-1191, and MRS-1523) also abolished shrinkage produced by 10 μM adenosine when all four known receptor subtypes are occupied. The A1-selective agonist N 6-cyclopentyladenosine exerted a small effect at 100 nM but not at higher or lower concentrations. The A2A agonist CGS-21680 triggered shrinkage only at high concentration (3 μM), an effect blocked by MRS-1191. IB-MECA increased intracellular Ca2+ in HCE cells and also stimulated short-circuit current across rabbit ciliary epithelium. A3 message was detected in both HCE cells and rabbit ciliary processes using RT-PCR. We conclude that human HCE cells and rabbit ciliary processes possess A3 receptors and that adenosine can activate Cl− channels in NPE cells by stimulating these A3receptors.
Incubation of OKP cells in low-K+ media increases NHE3 activity after early decrease in intracellular pH
Authors: Amemiya Morimasa , Tabei Kaoru , Kusano Eiji , Asano Yasushi , Alpern Robert J.
Published: December 2017

Chronic hypokalemia increases the activity of proximal tubule apical membrane Na+/H+antiporter NHE3. The present study examined the effect of the incubation of OKP cells (an opossum kidney, clone P cell line) in control medium {K+ concn ([K+]) = 5.4 mM} or low-K+ medium ([K+] = 2.7 mM) on NHE3. The activity of an ethylisopropyl amiloride-resistant Na+/H+antiporter, whose characteristics were consistent with those of NHE3, was increased in low-K+ cells beginning at 8 h. NHE3 mRNA and NHE3 protein abundance were increased 2.2-fold and 62%, respectively, at 24 h but not at 8 h. After incubation in low-K+ medium, intracellular pH (pHi) decreased by 0.27 pH units (maximum at 27 min) and then recovered to the control level. Intracellular acidosis induced by 5 mM sodium propionate increased Na+/H+antiporter activity at 8 and 24 h. Herbimycin A, a tyrosine kinase inhibitor, blocked low-K+- and sodium propionate-induced activation of the Na+/H+antiporter at 8 and 24 h. Our results demonstrate that low-K+ medium causes an early decrease in pHi, which leads to an increase in NHE3 activity via a tyrosine kinase pathway.
Monocytic cell necrosis is mediated by potassium depletion and caspase-like proteases
Authors: Warny Michel , Kelly Ciarán P.
Published: December 2017

Apoptosis is a physiological cell death that culminates in mitochondrial permeability transition and the activation of caspases, a family of cysteine proteases. Necrosis, in contrast, is a pathological cell death characterized by swelling of the cytoplasm and mitochondria and rapid plasma membrane disruption. Necrotic cell death has long been opposed to apoptosis, but it now appears that both pathways involve mitochondrial permeability transition, raising the question of what mediates necrotic cell death. In this study, we investigated mechanisms that promote necrosis induced by various stimuli ( Clostridium difficile toxins, Staphylococcus aureus alpha toxin, ouabain, nigericin) in THP-1 cells, a human monocytic cell line, and in monocytes. All stimuli induced typical features of necrosis and triggered protease-mediated release of interleukin-1β (IL-1β) and CD14 in both cell types. K+depletion was actively implicated in necrosis because substituting K+ for Na+ in the extracellular medium prevented morphological features of necrosis and IL-1β release. N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone, a broad-spectrum caspase inhibitor, prevented morphological features of necrosis, plasma membrane destruction, loss of mitochondrial membrane potential, IL-1β release, and CD14 shedding induced by all stimuli. Thus, in monocytic cells, necrosis is a cell death pathway mediated by passive K+ efflux and activation of caspase-like proteases.
Muscle LIM protein: expressed in slow muscle and induced in fast muscle by enhanced contractile activity
Authors: Schneider Achim G. , Sultan Karim R. , Pette Dirk
Published: December 2017

To identify early changes in gene expression during the fast-to-slow transition induced by chronic low-frequency stimulation, total RNA was extracted from 12-h-stimulated tibialis anterior (TA) muscles of rats and amplified by differential display RT-PCR. Among the signals of differentially expressed mRNAs, a cDNA ∼300 bp in length, which was almost undetectable in control TA muscles but prominent in stimulated TA and normal soleus muscles, was identified. This cDNA was cloned and identified as corresponding to the mRNA of the muscle LIM protein (MLP). Its differential expression in control, stimulated TA, and soleus muscles was verified by Northern blotting. Antibodies against MLP were used to identify by immunoblot analysis a protein of 22 kDa, the predicted molecular mass of MLP. Immunohistochemistry revealed strong reactivity for MLP in all fibers of normal soleus muscle and faint staining of some type IIA and type I fibers in control TA muscle. These fibers increased in number and staining intensity in 4-day-stimulated TA muscle. MLP thus seems to play an essential role during the rearrangement of cytoskeletal and/or myofibrillar structures in transforming adult muscle fibers.
ETB receptor activation leads to activation and phosphorylation of NHE3
Authors: Peng Y. , Moe O. W. , Chu T.-S. , Preisig P. A. , Yanagisawa M. , Alpern R. J.
Published: December 2017

In OKP cells expressing ETB endothelin receptors, activation of Na+/H+antiporter activity by endothelin-1 (ET-1) was resistant to low concentrations of ethylisopropyl amiloride, indicating regulation of Na+/H+exchanger isoform 3 (NHE3). ET-1 increased NHE3 phosphorylation in cells expressing ETB receptors but not in cells expressing ETAreceptors. Receptor specificity was not due to demonstrable differences in receptor-specific activation of tyrosine phosphorylation pathways or inhibition of adenylyl cyclase. Phosphorylation was associated with a decrease in mobility on SDS-PAGE, which was reversed by treating immunoprecipitated NHE3 with alkaline phosphatase. Phosphorylation was first seen at 5 min and was maximal at 15–30 min. Phosphorylation was maximal with 10−9 M ET-1. Phosphorylation occurred on threonine and serine residues at multiple sites. In summary, ET-1 induces NHE3 phosphorylation in OKP cells on multiple threonine and serine residues. ETB receptor specificity, time course, and concentration dependence are all similar between ET-1-induced increases in NHE3 activity and phosphorylation, suggesting that phosphorylation plays a key role in activation.
Mechanisms of Na+-K+pump regulation in cardiac myocytes during hyposmolar swelling
Authors: Bewick N. L. , Fernandes C. , Pitt A. D. , Rasmussen H. H. , Whalley D. W.
Published: December 2017

We have previously demonstrated that the sarcolemmal Na+-K+pump current ( I p) in cardiac myocytes is stimulated by cell swelling induced by exposure to hyposmolar solutions. However, the underlying mechanism has not been examined. Because cell swelling activates stretch-sensitive ion channels and intracellular messenger pathways, we examined their role in mediating I pstimulation during exposure of rabbit ventricular myocytes to a hyposmolar solution. I p was measured by the whole cell patch-clamp technique. Swelling-induced pump stimulation altered the voltage dependence of I p. Pump stimulation persisted in the absence of extracellular Na+ and under conditions designed to minimize changes in intracellular Ca2+, excluding an indirect influence on I pmediated via fluxes through stretch-activated channels. Pump stimulation was protein kinase C independent. The tyrosine kinase inhibitor tyrphostin A25, the phosphatidylinositol 3-kinase inhibitor LY-294002, and the protein phosphatase-1 and -2A inhibitor okadaic acid abolished I pstimulation. Our findings suggest that swelling-induced pump stimulation involves the activation of tyrosine kinase, phosphatidylinositol 3-kinase, and a serine/threonine protein phosphatase. Activation of this messenger cascade may cause activation by the dephosphorylation of pump units.
Acidic and basic troponin T isoforms in mature fast-twitch skeletal muscle and effect on contractility
Authors: Ogut Ozgur , Granzier Henk , Jin Jian-Ping
Published: December 2017

Developmentally regulated alternative RNA splicing generates distinct classes of acidic and basic troponin T (TnT) isoforms. In fast-twitch skeletal muscles, an acidic-to-basic TnT isoform switch ensures basic isoform expression in the adult. As an exception, an acidic segment in the NH2-terminal variable region of adult chicken breast muscle TnT isoforms is responsible for the unique exclusive expression of acidic TnTs in this muscle (O. Ogut and J.-P. Jin. J. Biol. Chem. 273: 27858–27866, 1998). To understand the relationship between acidic vs. basic TnT isoform expression and muscle contraction, the contractile properties of fibers from adult chicken breast muscle were compared with those of the levator coccygeus muscle, which expresses solely basic TnT isoforms. With use of Triton X-100-skinned muscle fibers, the force and stiffness responses to Ca2+ were measured. Relative to the levator coccygeus muscle, the breast muscle fibers showed significantly increased sensitivity to Ca2+ of force and stiffness with a shift of ∼0.15 in the pCa at which force or stiffness was 50% of maximal. The expression of tropomyosin, troponin I, and troponin C isoforms was also determined to delineate their contribution to thin-filament regulation. The data indicate that TnT isoforms differing in their NH2-terminal charge are able to alter the sensitivity of the myofibrillar contractile apparatus to Ca2+. These results provide evidence linking the regulated expression of distinct acidic and basic TnT isoform classes to the contractility of striated muscle.
TNF-α pretreatment prevents subsequent activation of cultured brain cells with TNF-α and hypoxia via ceramide
Authors: Ginis Irene , Schweizer Ulrich , Brenner Michael , Liu Jie , Azzam Nabil , Spatz Maria , Hallenbeck John M.
Published: December 2017

We have developed a cellular model in which cultured astrocytes and brain capillary endothelial cells preconditioned with tumor necrosis factor-α (TNF-α) fail to upregulate intercellular adhesion molecule-1 (ICAM-1) protein (80% inhibition) and mRNA (30% inhibition) when challenged with TNF-α or exposed to hypoxia. Inasmuch as ceramide is known to mediate some of the effects of TNF-α, its levels were measured at various times after the TNF-α preconditioning. We present evidence for the first time that, in normal brain cells, TNF-α pretreatment causes a biphasic increase of ceramide levels: an early peak at 15–20 min, when ceramide levels increased 1.9-fold in astrocytes and 2.7-fold in rat brain capillary endothelial cells, and a delayed 2- to 3-fold ceramide increase that occurs 18–24 h after addition of TNF-α. The following findings indicate that the delayed ceramide accumulation results in cell unresponsiveness to TNF-α: 1) coincident timing of the ceramide peak and the tolerance period, 2) mimicking of preconditioning by addition of exogenous ceramide, and 3) attenuation of preconditioning by fumonisin B1, an inhibitor of ceramide synthesis. In contrast to observations in transformed cell lines, the delayed ceramide increase was transient and did not induce apoptosis in brain cells.
TNF-α and insulin, alone and synergistically, induce plasminogen activator inhibitor-1 expression in adipocytes
Authors: Sakamoto Tomohiro , Woodcock-Mitchell Janet , Marutsuka Kousuke , Mitchell John J. , Sobel Burton E. , Fujii Satoshi
Published: December 2017

Obesity is associated with hyperinsulinemia and elevated concentrations of tumor necrosis factor-α (TNF-α) in adipose tissue. TNF-α has been implicated as an inducer of the synthesis of plasminogen activator inhibitor-1 (PAI-1), the primary physiological inhibitor of fibrinolysis, mediated by plasminogen activators in cultured adipocytes. To identify mechanism(s) through which TNF-α induces PAI-1, 3T3-L1 preadipocytes were differentiated into adipocytes and exposed to TNF-α for 24 h. TNF-α selectively increased the synthesis of PAI-1 without increasing activity of plasminogen activators. Both superoxide (generated by xanthine oxidase plus hypoxanthine) and hydrogen peroxide were potent inducers of PAI-1, and hydroxyl radical scavengers completely abolished the TNF-α induction of PAI-1. Exposure of adipocytes to TNF-α or insulin alone over 5 days increased PAI-1 production. These agonists exert synergistic effects. Results obtained suggest that TNF-α stimulates PAI-1 production by adipocytes, an effect potentiated by insulin, and that adipocyte generation of reactive oxygen centered radicals mediates the induction of PAI-1 production by TNF-α. Because induction of PAI-1 by TNF-α is potentiated synergistically by insulin, both agonists appear likely to contribute to the impairment of fibrinolytic system capacity typical in obese, hyperinsulinemic patients.
Metabolic acidosis regulates rat renal Na-Si cotransport activity
Authors: Puttaparthi Krishna , Markovich Daniel , Halaihel Nabil , Wilson Paul , Zajicek Hubert K. , Wang Huamin , Biber Jürg , Murer Heini , Rogers Thomas , Levi Moshe
Published: December 2017

Recently, we cloned a cDNA (NaSi-1) localized to rat renal proximal tubules and encoding the brush-border membrane (BBM) Na gradient-dependent inorganic sulfate (Si) transport protein (Na-Si cotransporter). The purpose of the present study was to determine the effect of metabolic acidosis (MA) on Na-Si cotransport activity and NaSi-1 protein and mRNA expression. In rats with MA for 24 h (but not 6 or 12 h), there was a significant increase in the fractional excretion of Si, which was associated with a 2.4-fold decrease in BBM Na-Sicotransport activity. The decrease in Na-Si cotransport correlated with a 2.8-fold decrease in BBM NaSi-1 protein abundance and a 2.2-fold decrease in cortical NaSi-1 mRNA abundance. The inhibitory effect of MA on BBM Na-Si cotransport was also sustained in rats with chronic (10 days) MA. In addition, in Xenopus laevis oocytes injected with mRNA from kidney cortex, there was a significant reduction in the induced Na-Si cotransport in rats with MA compared with control rats, suggesting that MA causes a decrease in the abundance of functional mRNA encoding the NaSi-1 cotransporter. These findings indicate that MA reduces Si reabsorption by causing decreases in BBM Na-Si cotransport activity and that decreases in the expression of NaSi-1 protein and mRNA abundance, at least in part, play an important role in the inhibition of Na-Si cotransport activity during MA.
Malignant human gliomas express an amiloride-sensitive Na+ conductance
Authors: Bubien James K. , Keeton Deborah A. , Fuller Catherine M. , Gillespie G. Yancey , Reddy Alyssa T. , Mapstone Timothy B. , Benos Dale J.
Published: December 2017

Human astrocytoma cells were studied using whole cell patch-clamp recording. An inward, amiloride-sensitive Na+ current was identified in four continuous cell lines originally derived from human glioblastoma cells (CH235, CRT, SKMG-1, and U251-MG) and in three primary cultures of cells obtained from glioblastoma multiforme tumors (up to 4 passages). In addition, cells freshly isolated from a resected medulloblastoma tumor displayed this same characteristic inward current. In contrast, amiloride-sensitive currents were not observed in normal human astrocytes, low-grade astrocytomas, or juvenile pilocytic astrocytomas. The only amiloride-sensitive Na+channels thus far molecularly identified in brain are the brain Na+ channels (BNaCs). RT-PCR analyses demonstrated the presence of mRNA for either BNaC1 or BNaC2 in these tumors and in normal astrocytes. These results indicate that the functional expression of amiloride-sensitive Na+ currents is a characteristic feature of malignant brain tumor cells and that this pathway may be a potentially useful target for therapeutic intervention.
Temporal responses of oxidative vs. glycolytic skeletal muscles to K+ deprivation: Na+ pumps and cell cations
Authors: Thompson Curtis B. , Choi Cheolsoo , Youn Jang H. , McDonough Alicia A.
Published: December 2017

When K+ output exceeds input, skeletal muscle releases intracellular fluid K+ to buffer the fall in extracellular fluid (ECF) K+. To investigate the mechanisms and muscle specificity of the K+ shift, rats were fed K+-deficient chow for 2–10 days, and two muscles at phenotypic extremes were studied: slow-twitch oxidative soleus and fast-twitch glycolytic white gastrocnemius (WG). After 2 days of low-K+ chow, plasma K+ concentration ([K+]) fell from 4.6 to 3.7 mM, and Na+-K+-ATPase α2 (not α1) protein levels in both muscles, measured by immunoblotting, decreased 36%. Cell [K+] decreased from 116 to 106 mM in soleus and insignificantly in WG, indicating that α2 can decrease before cell [K+]. After 5 days, there were further decreases in α2 (70%) and β2 (22%) in WG, not in soleus, whereas cell [K+] decreased and cell [Na+] increased by 10 mM in both muscles. By 10 days, plasma [K+] fell to 2.9 mM, with further decreases in WG α2 (94%) and β2 (70%); cell [K+] fell 19 mM in soleus and 24 mM in WG compared with the control, and cell [Na+] increased 9 mM in soleus and 15 mM in WG; total homogenate Na+-K+-ATPase activity decreased 19% in WG and insignificantly in soleus. Levels of α2, β1, and β2 mRNA were unchanged over 10 days. The ratios of α2 to α1 protein levels in both control muscles were found to be nearly 1 by using the relative changes in α-isoforms vs. β1- (soleus) or β2-isoforms (WG). We conclude that the patterns of regulation of Na+ pump isoforms in oxidative and glycolytic muscles during K+ deprivation mediated by posttranscriptional regulation of α2β1 and α2β2 are distinct and that decreases in α2-isoform pools can occur early enough in both muscles to account for the shift of K+ to the ECF.
Characterization of osteoblastic differentiation of stromal cell line ST2 that is induced by ascorbic acid
Authors: Otsuka Eri , Yamaguchi Akira , Hirose Shigehisa , Hagiwara Hiromi
Published: December 2017

The stromal cell line ST2, derived from mouse bone marrow, differentiated into osteoblast-like cells in response to ascorbic acid. Ascorbic acid induced alkaline phosphatase (ALPase) activity, the expression of mRNAs for proteins that are markers of osteoblastic differentiation, the deposition of calcium, and the formation of mineralized nodules by ST2 cells. We investigated the mechanism whereby ascorbic acid induced the differentiation of ST2 cells. Inhibitors of the formation of collagen triple helices completely blocked the effects of ascorbic acid on ST2 cells, an indication that matrix formation by type I collagen is essential for the induction of osteoblastic differentiation of ST2 cells by ascorbic acid. We furthermore examined the effects of bone morphogenetic proteins (BMPs) on the differentiation of ST2 cells induced by ascorbic acid. Ascorbic acid had no effect on the expression of mRNAs for BMP-4 and the BMP receptors. However, a soluble form of BMP receptor IA inhibited the induction of ALPase activity by ascorbic acid. These results suggest that ascorbic acid might promote the differentiation of ST2 cells into osteoblast-like cells by inducing the formation of a matrix of type I collagen, with subsequent activation of the signaling pathways that involve BMPs.
Focal adhesion proteins FAK and paxillin increase in hypertrophied skeletal muscle
Authors: Flück Martin , Carson James A. , Gordon Scott E. , Ziemiecki Andrew , Booth Frank W.
Published: December 2017

Components of signaling pathways for mechanotransduction during load-induced enlargement of skeletal muscle have not been completely defined. We hypothesized that loading of skeletal muscle would result in an adaptive increase in the expression of two focal adhesion complex (FAC)-related proteins, focal adhesion kinase (FAK) and paxillin, as well as increased FAK activity. FAK protein was immunolocalized to the sarcolemmal region of rooster anterior latissimus dorsi (ALD) myofibers in the middle of the ALD muscle. FAK (77 and 81%) and paxillin (206 and 202%) protein concentrations per unit of total protein in Western blots increased significantly after 1.5 and 7 days, but not after 13 days, of stretch-induced hypertrophy-hyperplasia of the ALD muscle. FAK autokinase activity in immunoprecipitates was increased after 1.5, 7, and 13 days in stretched ALD muscles. To determine whether increased FAK and paxillin protein concentrations are associated with hypertrophy and/or new fiber formation, two additional experiments were performed. First, during formation of primary chicken myotubes (a model of new fiber formation), FAK protein concentration (63%), FAK activity (157%), and paxillin protein concentration (97%) increased compared with myoblasts. Second, FAK (112% and 611%) and paxillin (87% and 431%) protein concentrations per unit of total protein in the soleus muscle increased at 1 and 8 days after surgical ablation of the synergistic gastrocnemius muscle (a model of hypertrophy without hyperplasia). Thus increases in components of the FAC occur in hypertrophying muscle of animals and in newly formed muscle fibers in culture. Furthermore, increased FAK activity suggests a possible convergence of signaling at the FAC in load-induced growth of skeletal muscle.
Ca2+ influx inhibits voltage-dependent and augments Ca2+-dependent K+ currents in arterial myocytes
Authors: Cox Robert H. , Petrou Steven
Published: December 2017

These experiments were performed to determine the effects of reducing Ca2+ influx (Cain) on K+ currents ( I K) in myocytes from rat small mesenteric arteries by 1) adding external Cd2+ or 2) lowering external Ca2+ to 0.2 mM. When measured from a holding potential (HP) of −20 mV ( I K20), decreasing Cain decreased I K at voltages where it was active (>0 mV). When measured from a HP of −60 mV ( I K60), decreasing Cain increased I K at voltages between −30 and +20 mV but decreased I K at voltages above +40 mV. Difference currents (Δ I K) were determined by digital subtraction of currents recorded under control conditions from those obtained when Cain was decreased. At test voltages up to 0 mV, Δ I K60 exhibited kinetics similar to control I K60, with rapid activation to a peak followed by slow inactivation. At 0 mV, peak Δ I K60 averaged 75 ± 13 pA ( n = 8) with Cd2+ and 120 ± 20 pA ( n = 9) with low Ca2+ concentration. At test voltages from 0 to +60 mV, Δ I K60 always had an early positive peak phase, but its apparent “inactivation” increased with voltage and its steady value became negative above +20 mV. At +60 mV, the initial peak Δ I K60 averaged 115 ± 18 pA with Cd2+ and 187 ± 34 pA with low Ca2+. With 10 mM pipette BAPTA, Cd2+ produced a small inhibition of I K20 but still increased I K60between −30 and +10 mV. In Ca2+-free external solution, Cd2+ only decreased both I K20 and I K60. In the presence of iberiotoxin (100 nM) to inhibit Ca2+-activated K+ channels (KCa), Cd2+ increased I K60 at all voltages positive to −30 mV while BAY K 8644 (1 μM) decreased I K60. These results suggest that Cain, through L-type Ca2+ channels and perhaps other pathways, increases KCa(i.e., I K20) and decreases voltage-dependent K+currents in this tissue. This effect could contribute to membrane depolarization and force maintenance.
Actively phosphorylating mitochondria are more resistant to lactic acidosis than inactive mitochondria
Authors: Tonkonogi M. , Sahlin K.
Published: December 2017

Oxidative phosphorylation of isolated rat skeletal muscle mitochondria after exposure to lactic acidosis in either phosphorylating or nonphosphorylating states has been evaluated. Mitochondrial respiration and transmembrane potential (ΔΨm) were measured with pyruvate and malate as the substrates. The addition of lactic acid decreased the pH of the reaction medium from 7.5 to 6.4. When lactic acid was added to nonphosphorylating mitochondria, the subsequent maximal ADP-stimulated respiration decreased by 27% compared with that under control conditions ( P < 0.05), and the apparent Michaelis-Menten constant ( K m) for ADP decreased to 10 μM vs. 20 μM ( P< 0.05) in controls. In contrast, maximal respiration and ADP sensitivity were not affected when mitochondria were exposed to acidosis during active phosphorylation in state 3. Acidosis significantly increased mitochondrial oxygen consumption in state 4 (post-state 3), irrespective of when acidosis was induced. This effect of acidosis was attenuated in the presence of oligomycin. The addition of lactic acid during state 4 respiration decreased ΔΨm by 19%. The ratio between added ADP and consumed oxygen (P/O) was close to the theoretical value of 3 in all conditions. The addition of potassium lactate during state 3 (i.e., medium pH unchanged) had no effect on the parameters measured. It is concluded that lactic acidosis has different effects when induced on nonphosphorylating vs. actively phosphorylating mitochondria. On the basis of these results, we suggest that the influence of lactic acidosis on muscle aerobic energy production depends on the physiological conditions at the onset of acidity.
Antagonism of CD95 signaling blocks butyrate induction of apoptosis in young adult mouse colonic cells
Authors: Fan Yang-Yi , Zhang Jianhu , Barhoumi Rola , Burghardt Robert C. , Turner Nancy D. , Lupton Joanne R. , Chapkin Robert S.
Published: December 2017

There is great interest in utilizing butyrate as a chemopreventive agent for colon tumorigenesis because of its ability to promote apoptosis in colon tumor cell lines. Because CD95 (APO-1/Fas) transduces signals resulting in apoptosis, we tested the hypothesis that butyrate-dependent colonocyte apoptosis is mediated by this death receptor. Butyrate (1 mM) exposure for 24 h upregulated expression of Fas and its ligand in young adult mouse colon (YAMC) cells. To delineate the proapoptotic effect of butyrate and to avoid the confounding effects of detachment from the extracellular matrix, adherent cell apoptosis was monitored as loss of plasma membrane asymmetry and dissipation of mitochondrial membrane potential (ΔΨmt) by laser cytometry. Soluble Fas receptor protein (Fas:Fc chimera) and caspase inhibitors (z-VAD-fmk and z-IETD-fmk) blocked butyrate induction of apoptosis. Treatment with Fas agonistic antibody (clone Jo-2) significantly induced cell death, indicating that Fas in colonocytes is functional. In addition, butyrate promoted apoptosis by inducing loss of ΔΨmt and phospholipid asymmetry of the plasma membrane after 12 and 24 h of exposure, respectively, before cell detachment. Therefore, Fas receptor-dependent signal transduction is involved in butyrate induction of apoptosis in colonocytes.
CFTR is functionally active in GnRH-expressing GT1–7 hypothalamic neurons
Authors: Weyler Richard T. , Yurko-Mauro Karin A. , Rubenstein Ronald , Kollen Wouter J. W. , Reenstra William , Altschuler Steven M. , Egan Marie , Mulberg Andrew E.
Published: December 2017

We have demonstrated the expression of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, mRNA, and protein within the rat and human brains, in areas regulating sexual differentiation and function. We have found that GT1–7, a gonadotropin-releasing hormone (GnRH)-secreting hypothalamic neuronal cell line, expresses the CFTR gene, mRNA, and protein and cAMP-dependent 36Cl efflux. A linear 7-pS Cl− conductance, which is stimulated by ATP and cAMP analogs and inhibited by glibenclamide, consistent with CFTR activity, has been identified in GT1–7 cells. Antisense oligo(dN) generated against exon 10 of the CFTR gene transcript (mRNA) inhibit GnRH secretion into media [312 ± 73, 850 ± 150, 963 ± 304, and 912 ± 74 pg GnRH/4 × 106 cells for antisense, sense, missense, and no oligo(dN), respectively; P < 0.029 for antisense oligo(dN)-treated vs. normal cells]. No changes in intracellular synthesis of GnRH were noted [1,400 ± 371 and 1,395 ± 384 pg GnRH/4 × 106 cells for antisense and sense oligo(dN), respectively]. Antisense oligo(dN), but not sense or missense oligo(dN), inhibited cAMP-dependent36Cl efflux. The expression of CFTR protein, detected by Western blotting, was also inhibited 68% by preincubation of cells with antisense oligo(dN). GT1–7 hypothalamic neurons express the CFTR gene, mRNA, and protein, which modulate neurosecretion. Abnormal neuropeptide vesicle trafficking by mutant CFTR may help to explain some of the diverse manifestations of cystic fibrosis.
Defective function of the cystic fibrosis-causing missense mutation G551D is recovered by genistein
Authors: Illek Beate , Zhang Lei , Lewis Nancy C. , Moss Richard B. , Dong Jian-Yun , Fischer Horst
Published: December 2017

The patch-clamp technique was used to investigate the effects of the isoflavone genistein on disease-causing mutations (G551D and ΔF508) of the cystic fibrosis transmembrane conductance regulator (CFTR). In HeLa cells recombinantly expressing the trafficking-competent G551D-CFTR, the forskolin-stimulated Cl currents were small, and average open probability of G551D-CFTR was P o = 0.047 ± 0.019. Addition of genistein activated Cl currents ∼10-fold, and the P o of G551D-CFTR increased to 0.49 ± 0.12, which is a P o similar to wild-type CFTR. In cystic fibrosis (CF) epithelial cells homozygous for the trafficking-impaired ΔF508 mutation, forskolin and genistein activated Cl currents only after 4-phenylbutyrate treatment. These data suggested that genistein activated CFTR mutants that were present in the cell membrane. Therefore, we tested the effects of genistein in CF patients with the G551D mutation in nasal potential difference (PD) measurements in vivo. The perfusion of the nasal mucosa of G551D CF patients with isoproterenol had no effect; however, genistein stimulated Cl-dependent nasal PD by, on average, −2.4 ± 0.6 mV, which corresponds to 16.9% of the responses (to β-adrenergic stimulation) found in healthy subjects.
Two types of voltage-dependent potassium channels in outer hair cells from the guinea pig cochlea
Authors: van den Abbeele Thierry , Teulon Jacques , Huy Patrice Tran Ba
Published: December 2017

Cell-attached and cell-free configurations of the patch-clamp technique were used to investigate the conductive properties and regulation of the major K+channels in the basolateral membrane of outer hair cells freshly isolated from the guinea pig cochlea. There were two major voltage-dependent K+ channels. A Ca2+-activated K+ channel with a high conductance (220 pS, P K/ P Na= 8) was found in almost 20% of the patches. The inside-out activity of the channel was increased by depolarizations above 0 mV and increasing the intracellular Ca2+concentration. External ATP or adenosine did not alter the cell-attached activity of the channel. The open probability of the excised channel remained stable for several minutes without rundown and was not altered by the catalytic subunit of protein kinase A (PKA) applied internally. The most frequent K+ channel had a low conductance and a small outward rectification in symmetrical K+ conditions (10 pS for inward currents and 20 pS for outward currents, P K/ P Na= 28). It was found significantly more frequently in cell-attached and inside-out patches when the pipette contained 100 μM acetylcholine. It was not sensitive to internal Ca2+, was inhibited by 4-aminopyridine, was activated by depolarization above −30 mV, and exhibited a rundown after excision. It also had a slow inactivation on ensemble-averaged sweeps in response to depolarizing pulses. The cell-attached activity of the channel was increased when adenosine was superfused outside the pipette. This effect also occurred with permeant analogs of cAMP and internally applied catalytic subunit of PKA. Both channels could control the cell membrane voltage of outer hair cells.
Loss of Hoxa5 gene function in mice perturbs intestinal maturation
Authors: Aubin Josée , Chailler Pierre , Ménard Daniel , Jeannotte Lucie
Published: December 2017

The Hox gene family of transcription factors constitutes candidate regulators in the molecular cascade of events that governs establishment of normal terminal differentiation along the duodenum to colon axis. One member of this family, Hoxa5, displays a dynamic pattern of expression during gut development. Hoxa5 transcripts are present in midgut mesenchyme at the time of remodeling, supporting a role for this gene in digestive tract specification. To study the role of Hoxa5 in proper intestinal development and maturation, we examined whether Hoxa5 mutant mice exhibit any defect in this process. We report here that even though Hoxa5 is not required for midgut morphogenesis, its loss of function perturbs the acquisition of adult mode of digestion, which normally is temporally coordinated with the process of spontaneous weaning. Impaired maturation of the digestive tract might be related to altered specification of intestinal epithelial cells. Our findings provide evidence that Hoxa5 expression in the gut mesoderm is important for the region-specific differentiation of the adjacent endoderm.
Vascular wall dysfunction in JCR:LA-cp rats: effects of age and insulin resistance
Authors: O'brien Sheila F. , Russell James C. , Davidge Sandra T.
Published: December 2017

We tested the hypothesis that aging and insulin resistance interact to increase vascular dysfunction by comparing the function of isolated mesenteric resistance arteries in obese, insulin-resistant JCR:LA-cp rats and lean, insulin-sensitive rats of the same strain at 3, 6, 9, and 12 mo of age. The peak constrictor responses to norepinephrine, phenylephrine, and high potassium were elevated in arteries from obese rats. Responses to these agents increased with age in both obese and lean rats. An eicosanoid constrictor contributed substantially to vasoconstriction in the arteries from both lean and obese animals. Inhibition of nitric oxide synthase increased the vasoconstrictor response to norepinephrine in both obese and lean rats. This effect increased with age in lean rats only. Vascular relaxation in response to acetylcholine and sodium nitroprusside was impaired in the obese rats and did not alter with age. The results suggest that obese JCR:LA-cp rats have enhanced maximal constriction, which originates in the arterial smooth muscle and increases with age. There is evidence that the ability of the arteries to compensate for the enhanced contractility is impaired in obese rats, particularly with advanced age.
Protein kinase D inhibits plasma membrane Na+/H+exchanger activity
Authors: Haworth Robert S. , Sinnett-Smith James , Rozengurt Enrique , Avkiran Metin
Published: December 2017

The regulation of plasma membrane Na+/H+exchanger (NHE) activity by protein kinase D (PKD), a novel protein kinase C- and phorbol ester-regulated kinase, was investigated. To determine the effect of PKD on NHE activity in vivo, intracellular pH (pHi) measurements were made in COS-7 cells by microepifluorescence using the pH indicator cSNARF-1. Cells were transfected with empty vector (control), wild-type PKD, or its kinase-deficient mutant PKD-K618M, together with green fluorescent protein (GFP). NHE activity, as reflected by the rate of acid efflux ( J H), was determined in single GFP-positive cells following intracellular acidification. Overexpression of wild-type PKD had no significant effect on J H(3.48 ± 0.25 vs. 3.78 ± 0.24 mM/min in control at pHi 7.0). In contrast, overexpression of PKD-K618M increased J H (5.31 ± 0.57 mM/min at pHi 7.0; P < 0.05 vs. control). Transfection with these constructs produced similar effects also in A-10 cells, indicating that native PKD may have an inhibitory effect on NHE in both cell types, which is relieved by a dominant-negative action of PKD-K618M. Exposure of COS-7 cells to phorbol ester significantly increased J H in control cells but failed to do so in cells overexpressing either wild-type PKD (due to inhibition by the overexpressed PKD) or PKD-K618M (because basal J Hwas already near maximal). A fusion protein containing the cytosolic regulatory domain (amino acids 637–815) of NHE1 (the ubiquitous NHE isoform) was phosphorylated in vitro by wild-type PKD, but with low stoichiometry. These data suggest that PKD inhibits NHE activity, probably through an indirect mechanism, and represents a novel pathway in the regulation of the exchanger.
Characterization and regulation of E2F activity during Caco-2 cell differentiation
Authors: Ding Qingming , Wang Qingding , Dong Zizheng , Evers B. Mark
Published: December 2017

The specific mechanisms controlling intestinal cell differentiation remain largely undefined. The retinoblastoma (Rb) proteins (pRb, p130, and p107) appear crucial to the terminal differentiation process of certain cells through their association and repression of E2F transcription factors. We have examined the expression of pRb-related proteins p130 and p107 as well as the regulation of E2F during spontaneous differentiation of the Caco-2 intestinal cell line. Nuclear protein levels of p130 and p107 were increased with Caco-2 differentiation. Induction of a slower-migrating E2F complex was noted in postconfluent (i.e., differentiated) Caco-2 cells; p130 protein was the predominant component of this E2F complex with a minor contribution from cyclin-dependent kinase-2. A small component of p107 binding was identified by deoxycholate release gel shift assays. In contrast, no pRb binding to E2F was noted in Caco-2 cells. In addition to increased association with p130, E2F-4 phosphorylation was markedly decreased in differentiated Caco-2 cells, whereas E2F protein levels remained unchanged. Taken together, our findings suggest that the regulation of E2F function may be an important contributing factor in the cell cycle block and spontaneous differentiation of Caco-2 cells. This regulation of E2F occurs most likely through its increased association with p130 as well as decreased phosphorylation.
Hypoxic preconditioning protects cultured neurons against hypoxic stress via TNF-α and ceramide
Authors: Liu Jie , Ginis Irene , Spatz Maria , Hallenbeck John M.
Published: December 2017

Brief “preconditioning” ischemia induces ischemic tolerance (IT) and protects the animal brain from subsequent otherwise lethal ischemia. Identification of the signaling steps most proximal to the development of the IT will allow induction of the resistance to ischemia shortly after the onset of stroke. Animal studies demonstrate a key role of tumor necrosis factor-α (TNF-α) in induction of IT. The sphingolipid ceramide is known as a second messenger in many of the multiple effects of TNF-α. We hypothesized that ceramide could mediate IT. We demonstrate that preconditioning of rat cortical neurons with mild hypoxia protects them from hypoxia and O2-glucose deprivation injury 24 h later (50% protection). TNF-α pretreatment could be substituted for hypoxic preconditioning (HP). HP was attenuated by TNF-α-neutralizing antibody. HP and TNF-α pretreatment cause a two- to threefold increase of intracellular ceramide levels, which coincides with the state of tolerance. Fumonisin B1, an inhibitor of ceramide synthase, attenuated ceramide upregulation and HP. C-2 ceramide added to the cultures right before the hypoxic insult mimicked the effect of HP. Ceramide did not induce apoptosis. These results suggest that HP is mediated via ceramide synthesis triggered by TNF-α.