bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure, function, and genomic organization of human Na+-dependent high-affinity dicarboxylate transporter
Authors: Wang Haiping , Fei You-Jun , Kekuda Ramesh , Yang-Feng Teresa L. , Devoe Lawrence D. , Leibach Frederick H. , Prasad Puttur D. , Ganapathy Vadivel
Published: December 2017

We have cloned and functionally characterized the human Na+-dependent high-affinity dicarboxylate transporter (hNaDC3) from placenta. The hNaDC3 cDNA codes for a protein of 602 amino acids with 12 transmembrane domains. When expressed in mammalian cells, the cloned transporter mediates the transport of succinate in the presence of Na+ [concentration of substrate necessary for half-maximal transport ( K t) for succinate = 20 ± 1 μM]. Dimethylsuccinate also interacts with hNaDC3. The Na+-to-succinate stoichiometry is 3:1 and concentration of Na+ necessary for half-maximal transport[Formula: see text]is 49 ± 1 mM as determined by uptake studies with radiolabeled succinate. When expressed in Xenopus laevis oocytes, hNaDC3 induces Na+-dependent inward currents in the presence of succinate and dimethylsuccinate. At a membrane potential of −50 mV,[Formula: see text] is 102 ± 20 μM and[Formula: see text]is 22 ± 4 mM as determined by the electrophysiological approach. Simultaneous measurements of succinate-evoked charge transfer and radiolabeled succinate uptake in hNaDC3-expressing oocytes indicate a charge-to-succinate ratio of 1:1 for the transport process, suggesting a Na+-to-succinate stoichiometry of 3:1. pH titration of citrate-induced currents shows that hNaDC3 accepts preferentially the divalent anionic form of citrate as a substrate. Li+inhibits succinate-induced currents in the presence of Na+. Functional analysis of rat-human and human-rat NaDC3 chimeric transporters indicates that the catalytic domain of the transporter lies in the carboxy-terminal half of the protein. The human NaDC3 gene is located on chromosome 20q12–13.1, as evidenced by fluorescent in situ hybridization. The gene is >80 kbp long and consists of 13 exons and 12 introns.
Vasopressin and PGE2 regulate activity of apical 70 pS K+ channel in thick ascending limb of rat kidney
Authors: Liu Hua Jun , Wei Yuan , Fererri Nicholas R. , Nasjletti Alberto , Wang Wen Hui
Published: December 2017

Vasopressin and prostaglandin E2 (PGE2) are involved in regulating NaCl reabsorption in the thick ascending limb (TAL) of the rat kidney. In the present study, we used the patch-clamp technique to study the effects of vasopressin and PGE2 on the apical 70 pS K+ channel in the rat TAL. Addition of vasopressin increased the channel activity, defined as NP o, from 1.11 to 1.52 (200 pM) and 1.80 (500 pM), respectively. The effect of vasopressin can be mimicked by either forskolin (1–5 μM) or 8-bromo-cAMP/dibutyryl-cAMP (8-Br-cAMP/DBcAMP) (200–500 μM). Moreover, the effects of cAMP and vasopressin were not additive and application of 10 μM H-89 abolished the effect of vasopressin. This suggests that the effect of vasopressin is mediated by a cAMP-dependent pathway. Applying 10 nM PGE2 alone had no significant effect on the channel activity. However, PGE2 (10 nM) abolished the stimulatory effect of vasopressin. The PGE2-induced inhibition of the vasopressin effect was the result of decreasing cAMP production because addition of 200 μM 8-Br-cAMP/DBcAMP reversed the PGE2-induced inhibition. In addition to antagonizing the vasopressin effect, high concentrations of PGE2 reduced channel activity in the absence of vasopressin by 33% (500 nM) and 51% (1 μM), respectively. The inhibitory effect of high concentrations of PGE2 was not the result of decreasing cAMP production because adding the membrane-permeant cAMP analog failed to restore the channel activity. In contrast, inhibiting protein kinase C (PKC) with calphostin C (100 nM) abolished the effect of 1 μM PGE2. We conclude that PGE2 inhibits apical K+ channels by two mechanisms: 1) low concentrations of PGE2 attenuate the vasopressin-induced stimulation mainly by reducing cAMP generation, and 2) high concentrations of PGE2 inhibit the channel activity by a PKC-dependent pathway.
Limited myogenic response to a single bout of weight-lifting exercise in old rats
Authors: Tamaki Tetsuro , Uchiyama Shuichi , Uchiyama Yoshiyasu , Akatsuka Akira , Yoshimura Shinichi , Roy Roland R. , Edgerton V. Reggie
Published: December 2017

The purpose of the present study was to compare the myogenic response of hindlimb muscles in young (14–20 wk of age) and old (>120 wk of age) rats with a single exhaustive bout of heavy resistance weight lifting. [3H]thymidine and [14C]leucine labeling were monitored for up to 2 wk after the exercise bout to estimate serial changes in mitotic activity and the level of amino acid uptake and myosin synthesis. Histological, histochemical, and immunohistochemical [anti-5-bromo-2′-deoxyuridine and myogenic determination genes (MyoD)] analyses of whole muscles and analysis of muscle-specific gene expression (MyoD) using Western blotting and RT-PCR were performed. Old rats showed significant muscle atrophy and a lower exercise capacity than young rats. Exercise-induced muscle damage, as assessed in histological sections, and increases in serum creatine kinase activity were evident in both young and old exercised groups. Mitotic activity was increased in young, but not old, rats 2 days after exercise. There was a biphasic increase in [14C]leucine uptake during the 14 days postexercise (peaks at 1–4 and 10 days) in young rats: only the first peak was observed in old rats. There was a lower uptake of [14C]leucine in the myosin fraction and an impaired expression of MyoD at the protein (immunohistochemistry and Western blotting) and mRNA (RT-PCR) levels in old rats throughout the postexercise period. These results demonstrate a reduced reparative capability of muscle in response to a single bout of exercise in old compared with young rats.
150-kDa oxygen-regulated protein (ORP150) functions as a novel molecular chaperone in MDCK cells
Authors: Bando Yoshio , Ogawa Satoshi , Yamauchi Atsushi , Kuwabara Keisuke , Ozawa Kentaro , Hori Osamu , Yanagi Hideki , Tamatani Michio , Tohyama Masaya
Published: December 2017

To assess the participation of the 150-kDa oxygen-regulated protein (ORP150) in protein transport, its function in Madin-Darby canine kidney (MDCK) cells was studied. Exposure of MDCK cells to hypoxia resulted in an increase of ORP150 antigen and increased binding of ORP150 to GP80/clusterin (80-kDa glycoprotein), a natural secretory protein in this cell line. In ORP150 antisense transformant MDCK cells, GP80 was retained within the endoplasmic reticulum after exposure to hypoxia. Metabolic labeling showed the delay of GP80 maturation in antisense transformants in hypoxia, whereas its matured form was detected in wild-type cells, indicating a role of ORP150 in protein transport, especially in hypoxia. The affinity chromatographic analysis of ORP150 suggested its ability to bind to ATP-agarose. Furthermore, the ATP hydrolysis analysis showed that ORP150 can release GP80 at a lower ATP concentration. These data indicate that ORP150 may function as a unique molecular chaperone in renal epithelial cells by facilitating protein transport/maturation in an environment where less ATP is accessible.
Cloning of murine glycosyl phosphatidylinositol anchor attachment protein, GPAA1
Authors: Hiroi Y. , Chen R. , Sawa H. , Hosoda T. , Kudoh S. , Kobayashi Y. , Aburatani H. , Nagashima K. , Nagai R. , Yazaki Y. , Medof M. E. , Komuro I.
Published: December 2017

Glycosyl phosphatidylinositols (GPIs) are used to anchor many proteins to the cell surface membrane and are utilized in all eukaryotic cells. GPI anchoring units are attached to proteins via a transamidase reaction mediated by a GPI transamidase complex. We isolated one of the components of this complex, mGPAA1 (murine GPI anchor attachment), by the signal sequence trap method. mGPAA1 cDNA is about 2 kb in length and encodes a putative 621 amino acid protein. The mGPAA1gene has 12 small exons and 11 small introns. mGPAA1 mRNA is ubiquitously expressed in mammalian cells, and in situ hybridization analysis revealed that it is abundant in the choroid plexus, skeletal muscle, osteoblasts of rib, and occipital bone in mouse embryos. Its expression levels and transamidation efficiency decreased with differentiation of embryonic stem cells. The 3T3 cell lines expressing antisense mGPAA1 failed to express GPI-anchored proteins on the cell surface membrane.
Insight into the mechanism by which metoclopramide improves immune functions after trauma-hemorrhage
Authors: Knöferl Markus W. , Angele Martin K. , Ayala Alfred , Cioffi William G. , Bland Kirby I. , Chaudry Irshad H.
Published: December 2017

Although studies have shown that prolactin (Prl) and metoclopramide (Mcp) administration restores the depressed cell-mediated immune functions after hemorrhage, the underlying mechanism responsible for the immunostimulatory effects of Mcp remains unknown. We hypothesized that Mcp improves immune responses by upregulating the secretion of Prl. To test this hypothesis, male C3H/HeN mice were subjected to sham operation or laparotomy (i.e., soft tissue trauma) and hemorrhagic shock (Hem; 35 ± 5 mmHg for 90 min) and then resuscitated. Plasma Prl levels were determined 30 min after Mcp (1 μg/g body wt sc at end of Hem) or vehicle (Veh) treatment in sham and Hem mice. The results indicate that plasma Prl levels increased significantly in Mcp-treated mice (sham-Veh 249.9 ± 5.3, Hem-Veh 229.9 ± 7.6, Hem-Mcp 596.9 ± 73.1 ng/ml, one-way ANOVA, P < 0.05 vs. Veh). To determine whether Mcp produces its salutary effects directly or indirectly via increased Prl secretion, splenocyte proliferation and splenocyte interleukin (IL)-2 and IL-3 release from untreated sham or Hem mice were determined in the presence of increasing concentrations of mouse Prl or Mcp. The addition of Mcp had no effect on splenocyte immune functions in vitro. However, the addition of Prl restored the hemorrhage-induced depressed splenocyte proliferation as well as splenocyte IL-2 and IL-3 release in vitro in a dose-dependent manner. Thus the beneficial effects of Mcp on immune functions after Hem appear to be mediated by Prl. Because Mcp increases plasma levels of the immunoenhancing hormone Prl, this agent should be considered a useful adjunct for the treatment of immunodepression in trauma victims.
Antithrombin reduces leukocyte adhesion during chronic endotoxemia by modulation of the cyclooxygenase pathway
Authors: Hoffmann J. N. , Vollmar B. , Inthorn D. , Schildberg F. W. , Menger M. D.
Published: December 2017

Antithrombin (AT) is known as the most important natural inhibitor of thrombin activity and has been shown to improve distinct clinical parameters during the course of septic (endotoxin)-induced multiple organ dysfunction. We hypothesized that AT acts by inhibiting leukocyte activation and microvascular injury via the promotion of endothelial release of PGI2, and therefore, we studied the effects of AT on leukocyte/endothelial cell interaction and microvascular perfusion during endotoxemia. In a skinfold preparation of Syrian hamsters, severe endotoxemia was induced by repeated administration of endotoxin intravenously [lipopolysaccharide (LPS), Escherichia coli, 2 mg/kg] at 0 and 48 h. AT (250 IU/kg) was administered intravenously at 0, 24, and 48 h ( n = 6, AT group). In control animals ( n = 5, control), LPS was given without AT supplementation. By intravital fluorescence microscopy, leukocyte-endothelial cell interaction and functional capillary density (FCD; measure of capillary perfusion) were analyzed during a 72-h period after the first LPS injection. AT significantly attenuated LPS-induced arteriolar and venular leukocyte adherence after both the first and the second LPS injection [ P < 0.01, measures analysis of variance (MANOVA)]. In parallel, AT was effective in preventing LPS-induced depression of FCD after the first and the second LPS administration ( P < 0.05, MANOVA). By pretreatment with the cyclooxygenase inhibitor indomethacin ( n = 6), effects of AT on leukocyte adherence and FCD were found completely abolished. Thus our study indicates that AT exerts its beneficial effects in endotoxemia by reducing leukocyte-endothelial cell interaction and microvascular perfusion failure probably via liberation of prostacyclin from endothelial cells.
Pharmacological modulation of ion transport across wild-type and ΔF508 CFTR-expressing human bronchial epithelia
Authors: Devor Daniel C. , Bridges Robert J. , Pilewski Joseph M.
Published: December 2017

Forskolin, UTP, 1-ethyl-2-benzimidazolinone (1-EBIO), NS004, 8-methoxypsoralen (Methoxsalen; 8-MOP), and genistein were evaluated for their effects on ion transport across primary cultures of human bronchial epithelium (HBE) expressing wild-type (wt HBE) and ΔF508 (ΔF-HBE) cystic fibrosis transmembrane conductance regulator. In wt HBE, the baseline short-circuit current ( I sc) averaged 27.0 ± 0.6 μA/cm2 ( n = 350). Amiloride reduced this I sc by 13.5 ± 0.5 μA/cm2 ( n = 317). In ΔF-HBE, baseline I sc was 33.8 ± 1.2 μA/cm2 ( n = 200), and amiloride reduced this by 29.6 ± 1.5 μA/cm2 ( n = 116), demonstrating the characteristic hyperabsorption of Na+ associated with cystic fibrosis (CF). In wt HBE, subsequent to amiloride, forskolin induced a sustained, bumetanide-sensitive I sc(Δ I sc = 8.4 ± 0.8 μA/cm2; n = 119). Addition of acetazolamide, 5-( N-ethyl- N-isopropyl)-amiloride, and serosal 4,4′-dinitrostilben-2,2′-disulfonic acid further reduced I sc, suggesting forskolin also stimulates HCO3 − secretion. This was confirmed by ion substitution studies. The forskolin-induced I scwas inhibited by 293B, Ba2+, clofilium, and quinine, whereas charybdotoxin was without effect. In ΔF-HBE the forskolin I sc response was reduced to 1.2 ± 0.3 μA/cm2 ( n = 30). In wt HBE, mucosal UTP induced a transient increase in I sc (Δ I sc = 15.5 ± 1.1 μA/cm2; n = 44) followed by a sustained plateau, whereas in ΔF-HBE the increase in I sc was reduced to 5.8 ± 0.7 μA/cm2 ( n = 13). In wt HBE, 1-EBIO, NS004, 8-MOP, and genistein increased I sc by 11.6 ± 0.9 ( n = 20), 10.8 ± 1.7 ( n = 18), 10.0 ± 1.6 ( n = 5), and 7.9 ± 0.8 μA/cm2( n = 17), respectively. In ΔF-HBE, 1-EBIO, NS004, and 8-MOP failed to stimulate Cl− secretion. However, addition of NS004 subsequent to forskolin induced a sustained Cl−secretory response (2.1 ± 0.3 μA/cm2, n = 21). In ΔF-HBE, genistein alone stimulated Cl− secretion (2.5 ± 0.5 μA/cm2, n = 11). After incubation of ΔF-HBE at 26°C for 24 h, the responses to 1-EBIO, NS004, and genistein were all potentiated. 1-EBIO and genistein increased Na+ absorption across ΔF-HBE, whereas NS004 and 8-MOP had no effect. Finally, Ca2+-, but not cAMP-mediated agonists, stimulated K+ secretion across both wt HBE and ΔF-HBE in a glibenclamide-dependent fashion. Our results demonstrate that pharmacological agents directed at both basolateral K+ and apical Cl− conductances directly modulate Cl−secretion across HBE, indicating they may be useful in ameliorating the ion transport defect associated with CF.
Properties and submitochondrial localization of pig and rat renal phosphate-activated glutaminase
Authors: Roberg Bjørg , Torgner Ingeborg A. , Laake Jon , Takumi Yutaka , Ottersen Ole P. , Kvamme Elling
Published: December 2017

Two pools of phosphate-activated glutaminase (PAG) were separated from pig and rat renal mitochondria. The partition of enzyme activity corresponded with that of the immunoreactivity and also with the postembedding immunogold labeling of PAG, which was associated partly with the inner membrane and partly with the matrix. The outer membrane was not labeled. PAG in intact mitochondria showed enzymatic characteristics that were similar to that of the membrane fraction and also mimicked that of the polymerized form of purified pig renal PAG. PAG in the soluble fraction showed properties similar to that of the monomeric form of purified enzyme. It is indicated that the pool of PAG localized inside the inner mitochondrial membrane is dormant due to the presence of high concentrations of the inhibitor glutamate. Thus the enzymatically active PAG is assumed to be localized on the outer face of the inner mitochondrial membrane. The activity of this pool of PAG appears to be regulated by compounds in the cytosol, of which glutamate may be most important.
Dependence of KCC2 K-Cl cotransporter activity on a conserved carboxy terminus tyrosine residue
Authors: Strange Kevin , Singer Thomas D. , Morrison Rebecca , Delpire Eric
Published: December 2017

K-Cl cotransporters (KCC) play fundamental roles in ionic and osmotic homeostasis. To date, four mammalian KCC genes have been identified. KCC2 is expressed exclusively in neurons. Injection of Xenopus oocytes with KCC2 cRNA induced a 20-fold increase in Cl−-dependent, furosemide-sensitive K+ uptake. Oocyte swelling increased KCC2 activity 2–3 fold. A canonical tyrosine phosphorylation site is located in the carboxy termini of KCC2 (R1081–Y1087) and KCC4, but not in other KCC isoforms. Pharmacological studies, however, revealed no regulatory role for phosphorylation of KCC2 tyrosine residues. Replacement of Y1087 with aspartate or arginine dramatically reduced K+ uptake under isotonic and hypotonic conditions. Normal or near-normal cotransporter activity was observed when Y1087 was mutated to phenylalanine, alanine, or isoleucine. A tyrosine residue equivalent to Y1087 is conserved in all identified KCCs from nematodes to humans. Mutation of the Y1087 congener in KCC1 to aspartate also dramatically inhibited cotransporter activity. Taken together, these results suggest that replacement of Y1087 and its congeners with charged residues disrupts the conformational state of the carboxy terminus. We postulate that the carboxy terminus plays an essential role in maintaining the functional conformation of KCC cotransporters and/or is involved in essential regulatory protein-protein interactions.
Desmin knockout muscles generate lower stress and are less vulnerable to injury compared with wild-type muscles
Authors: Sam Michel , Shah Sameer , Fridén Jan , Milner Derek J. , Capetanaki Yassemi , Lieber Richard L.
Published: December 2017

The functional role of the skeletal muscle intermediate filament system was investigated by measuring the magnitude of muscle force loss after cyclic eccentric contraction (EC) in normal and desmin null mouse extensor digitorum longus muscles. Isometric stress generated was significantly greater in wild-type (313 ± 8 kPa) compared with knockout muscles (276 ± 13 kPa) before EC ( P < 0.05), but 1 h after 10 ECs, both muscle types generated identical levels of stress (∼250 kPa), suggesting less injury to the knockout. Differences in injury susceptibility were not explained by the different absolute stress levels imposed on wild-type versus knockout muscles (determined by testing older muscles) or by differences in fiber length or mechanical energy absorbed. Morphometric analysis of longitudinal electron micrographs indicated that Z disks from knockout muscles were more staggered (0.36 ± 0.03 μm) compared with wild-type muscles (0.22 ± 0.03 μm), which may indicate that the knockout cytoskeleton is more compliant. These data demonstrate that lack of the intermediate filament system decreases isometric stress production and that the desmin knockout muscle is less vulnerable to mechanical injury.
Cyclic stretch activates p38 SAPK2-, ErbB2-, and AT1-dependent signaling in bladder smooth muscle cells
Authors: Nguyen Hiep T. , Adam Rosalyn M. , Bride Samuel H. , Park John M. , Peters Craig A. , Freeman Michael R.
Published: December 2017

Cyclic mechanical stretch of bladder smooth muscle cells (SMC) increases rates of DNA synthesis and stimulates transcription of the gene for heparin-binding epidermal growth factor-like growth factor (HB-EGF), an ErbB1/EGF receptor ligand that has been linked to hypertrophic bladder growth. In this study we sought to clarify the signaling pathways responsible for mechanotransduction of the stretch stimulus. HB-EGF mRNA levels, DNA synthesis, and AP-1/Ets DNA binding activities were induced by repetitive stretch of primary culture rat bladder SMC. Inhibitors of the p38 SAPK2 pathway, the angiotensin receptor type 1 (AT1), and the ErbB2 tyrosine kinase reduced each of these activities, while an inhibitor of the extracellular signal-regulated kinase mitogen-activated protein kinase (Erk-MAPK) pathway had no effect. Stretch rapidly activated stress-activated protein kinase 2 (p38 SAPK2) and Jun NH2-terminal kinase (JNK)/SAPK pathways but not the Erk-MAPK pathway and induced ErbB2 but not ErbB1 phosphorylation. Angiotensin II (ANG II) a bladder SMC mitogen previously linked to the stretch response, did not activate ErbB2, and ErbB2 activation occurred in response to stretch in the presence of an ANG receptor inhibitor, indicating that activation of the AT1-mediated pathway and the ErbB2-dependent pathway occurs by independent mechanisms. p38 SAPK2 and JNK/SAPK signaling also appeared to be independent of the ErbB2 and AT1 pathways. These findings indicate that stretch-stimulated DNA synthesis and gene expression in normal bladder SMC occur via multiple independent receptor systems (e.g., AT1 and ErbB2) and at least one MAPK pathway (p38 SAPK2). Further, we show that the Erk-MAPK pathway, which in most systems is linked to receptor-dependent cell growth responses, is not involved in progression to DNA synthesis or in the response of the HB-EGF gene to mechanical forces.
Expression of P2X7 purinoceptors on human lymphocytes and monocytes: evidence for nonfunctional P2X7 receptors
Authors: Gu B. J. , Zhang W. Y. , Bendall L. J. , Chessell I. P. , Buell G. N. , Wiley J. S.
Published: December 2017

Lymphocytes from normal subjects and patients with B-chronic lymphocytic leukemia (B-CLL) show functional responses to extracellular ATP characteristic of the P2X7 receptor (previously termed P2Z). These responses include opening of a cation-selective channel/pore that allows entry of the fluorescent dye ethidium and activation of a membrane metalloprotease that sheds the adhesion molecule L-selectin. The surface expression of P2X7receptors was measured in normal leucocytes, platelets, and B-CLL lymphocytes and correlated with their functional responses. Monocytes showed four- to fivefold greater expression of P2X7 than B, T, and NK lymphocytes, whereas P2X7 expression on neutrophils and platelets was weak. All cell types demonstrated abundant intracellular expression of this receptor. All 12 subjects with B-CLL expressed lymphocyte P2X7 at about the same level as B lymphocytes from normal subjects. P2X7 function, measured by ATP-induced uptake of ethidium, correlated closely with surface expression of this receptor in normal and B-CLL lymphocytes and monocytes ( n = 47, r = 0.70; P< 0.0001). However, in three patients the ATP-induced uptake of ethidium into the malignant B lymphocytes was low or absent. The lack of P2X7 function in these B lymphocytes was confirmed by the failure of ATP to induce Ba2+ uptake into their lymphocytes. This lack of function of the P2X7 receptor resulted in a failure of ATP-induced shedding of L-selectin, an adhesion molecule that directs the recirculation of lymphocytes from blood into the lymph node.
Bioenergetics and mitochondrial transmembrane potential during differentiation of cultured osteoblasts
Authors: Komarova Svetlana V. , Ataullakhanov Fasoil I. , Globus Ruth K.
Published: December 2017

To evaluate the relationship between osteoblast differentiation and bioenergetics, cultured primary osteoblasts from fetal rat calvaria were grown in medium supplemented with ascorbate to induce differentiation. Before ascorbate treatment, the rate of glucose consumption was 320 nmol · h−1 · 106cells−1, respiration was 40 nmol · h−1 · 106cells−1, and the ratio of lactate production to glucose consumption was ∼2, indicating that glycolysis was the main energy source for immature osteoblasts. Ascorbate treatment for 14 days led to a fourfold increase in respiration, a threefold increase in ATP production, and a fivefold increase in ATP content compared with that shown in immature cells. Confocal imaging of mitochondria stained with a transmembrane potential-sensitive vital dye showed that mature cells possessed abundant amounts of high-transmembrane-potential mitochondria, which were concentrated near the culture medium-facing surface. Acute treatment of mature osteoblasts with metabolic inhibitors showed that the rate of glycolysis rose to maintain the cellular energy supply constant. Thus progressive differentiation coincided with changes in cellular metabolism and mitochondrial activity, which are likely to play key roles in osteoblast function.
Contraction-induced injury to single permeabilized muscle fibers from mdx, transgenic mdx, and control mice
Authors: Lynch Gordon S. , Rafael Jill A. , Chamberlain Jeffrey S. , Faulkner John A.
Published: December 2017

Muscle fibers of mdx mice that lack dystrophin are more susceptible to contraction-induced injury, particularly when stretched. In contrast, transgenic mdx (tg -mdx) mice, which overexpress dystrophin, show no morphological or functional signs of dystrophy. Permeabilization disrupts the sarcolemma of fibers from muscles of mdx, tg- mdx, and control mice. We tested the null hypothesis stating that, after single stretches of maximally activated single permeabilized fibers, force deficits do not differ among fibers from extensor digitorum longus muscles of mdx, tg -mdx, or control mice. Fibers were maximally activated by Ca2+ (pCa 4.5) and then stretched through strains of 10%, 20%, or 30% of fiber length ( L f) at a velocity of 0.5 L f/s. Immediately after each strain, the force deficits were not different for fibers from each of the three groups of mice. When collated with studies of membrane-intact fibers in whole muscles of mdx, tg -mdx, and control mice, these results indicate that dystrophic symptoms do not arise from factors within myofibrils but, rather, from disruption of the sarcolemmal integrity that normally provides protection from contraction-induced injury.
Oxidants and regulation of K+-Cl−cotransport in equine red blood cells
Authors: Muzyamba M. C. , Speake P. F. , Gibson J. S.
Published: December 2017

The effect of oxidants on K+-Cl− cotransport (KCC) was investigated in equine red blood cells. Carbon monoxide mimicked O2. The substituted benzaldehyde, 12C79 (5 mM), markedly increased O2 affinity. In N2, however, O2 saturation was low (<10%) but KCC remained active. Nitrite (NO2 −) oxidized heme to methemoglobin (metHb). High concentrations of NO2 − (1 and 5 mM vs. 0.5 mM) increased KCC activity above control levels; it became O2independent but remained sensitive to other stimuli. 1-Chloro-2,4-dinitrobenzene (1–3 mM) depleted reduced glutathione (GSH). Prolonged exposure (60–120 min, 1 mM) or high concentrations (3 mM) stimulated an O2-independent KCC activity; short exposures and low concentrations (30 min, 0.5 or 1 mM) did not. The effect of these manipulations was correlated with changes in GSH and metHb concentrations. An oxy conformation of Hb was necessary for KCC activation. An increase in its activity over the level found in oxygenated control cells required both accumulation of metHb and depletion of GSH. Findings are relevant to understanding the physiology and pathology of regulation of KCC.
Intracellular ATP slows time-dependent decline of muscarinic cation current in guinea pig ileal smooth muscle
Authors: Inoue Ryuji , Ito Yushi
Published: December 2017

The effects of intracellular nucleotide triphosphates on time-dependent changes in muscarinic receptor cation currents ( I cat) were investigated using the whole cell patch-clamp technique in guinea pig ileal muscle. In the absence of nucleotide phosphates in the patch pipette, I cat evoked every 10 min decayed progressively. This decay was slowed dose dependently by inclusion of millimolar concentrations of ATP in the pipette. This required a comparable concentration of Mg2+, was mimicked by UTP and CTP, and was attenuated by simultaneous application of alkaline phosphatase or inhibitors of tyrosine kinase. In contrast, a sudden photolytic release of millimolar ATP (probably in the free form) caused a marked suppression of I cat. Submillimolar concentrations of GTP dose dependently increased the amplitude of I cat as long as ATP and Mg2+ were in the pipette, but, in their absence, GTP was ineffective at preventing I cat decay. The decay of I cat was paralleled by altered voltage-dependent gating, i.e., a positive shift in the activation curve and reduction in the maximal conductance. It is thus likely that ATP exerts two reciprocal actions on I cat, through Mg2+-dependent and -independent mechanisms, and that the enhancing effect of GTP on I cat is essentially different from that of ATP.
A hyperpolarization- and acid-activated nonselective cation current in Xenopus oocytes
Authors: Kuruma Akinori , Hirayama Yoshiyuki , Hartzell H. Criss
Published: December 2017

Heterologous expression of a variety of membrane proteins in Xenopus oocytes sometimes results in the appearance of a hyperpolarization-activated inward current. The nature of this current remains incompletely understood. Some investigators have suggested that this current is a Cl current, whereas others have identified it as a nonselective cation current. The purpose of this investigation was to characterize this current in more detail. The hyperpolarization-activated inward current ( I IN) present in native oocytes was composed of a current carried at least partly by Ca and Mg under physiological ionic conditions plus a Ca-activated Cl current. The Ca-activated Cl current was blocked by chelation of cytosolic Ca with 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid. When Cl currents were blocked, the cation current could be carried by Ca, Mg, or Co, but not appreciably by Ba, Mn, or Cd. I IN was stimulated by intracellular acidification. The properties of I IN were quite different from those of the store-operated Ca current. Heterologous expression of transient receptor potential-like gene product (TRPL), one of the members of the transient receptor potential family of putative store-operated Ca channels, apparently resulted in alteration of the voltage sensitivity of the endogenous I IN.
Guanine nucleotide transport by atractyloside-sensitive and -insensitive carriers in isolated heart mitochondria
Authors: McKee Edward E. , Bentley Alice T. , Smith Ronald M. , Kraas Jonathan R. , Ciaccio Christina E.
Published: December 2017

In previous work (McKee EE, Bentley AT, Smith RM Jr, and Ciaccio CE, Biochem Biophys Res Commun 257: 466–472, 1999), the transport of guanine nucleotides into the matrix of intact isolated heart mitochondria was demonstrated. In this study, the time course and mechanisms of guanine nucleotide transport are characterized. Two distinct mechanisms of transport were found to be capable of moving guanine nucleotides across the inner membrane. The first carrier was saturable, displayed temperature dependence, preferred GDP to GTP, and did not transport GMP or IMP. When incubated in the absence of exogenous ATP, this carrier had a V max of 946 ± 53 pmol · mg−1 · min−1 with a K m of 2.9 ± 0.3 mM for GDP. However, transport of GTP and GDP on this carrier was completely inhibited by physiological concentrations of ATP, suggesting that this carrier was not involved with guanine nucleotide transport in vivo. Because transport on this carrier was also inhibited by atractyloside, this carrier was consistent with the well-characterized ATP/ADP translocase. The second mechanism of guanine nucleotide uptake was insensitive to atractyloside, displayed temperature dependence, and was capable of transporting GMP, GDP, and GTP at approximately equal rates but did not transport IMP, guanine, or guanosine. GTP transport via this mechanism was slow, with a V max of 48.7 ± 1.4 pmol · mg−1 · min−1 and a K m = 4.4 ± 0.4 mM. However, because the requirement for guanine nucleotide transport is low in nondividing tissues such as the heart, this transport process is nevertheless sufficient to account for the matrix uptake of guanine nucleotides and may represent the physiological mechanism of transport.
Flow-induced expression of endothelial Na-K-Cl cotransport: dependence on K+ and Cl− channels
Authors: Suvatne Jimmy , Barakat Abdul I. , O'Donnell Martha E.
Published: December 2017

Steady laminar shear stress has been shown previously to markedly increase Na-K-Cl cotransporter mRNA and protein in human umbilical vein endothelial cells and also to rapidly increase endothelial K+ and Cl− channel conductances. The present study was done to evaluate the effects of shear stress on Na-K-Cl cotransporter activity and protein expression in bovine aortic endothelial cells (BAEC) and to determine whether changes in cotransporter expression may be dependent on early changes in K+ and Cl− channel conductances. Confluent BAEC monolayers were exposed in a parallel-plate flow chamber to either steady shear stress (19 dyn/cm2) or purely oscillatory shear stress (0 ± 19 dyn/cm2) for 6–48 h. After shearing, BAEC monolayers were assessed for Na-K-Cl cotransporter activity or were subjected to Western blot analysis of cotransporter protein. Steady shear stress led to a 2- to 4-fold increase in BAEC cotransporter protein levels and a 1.5- to 1.8-fold increase in cotransporter activity, increases that were sustained over the longest time periods studied. Oscillatory flow, in contrast, had no effect on cotransporter protein levels. In the presence of flow-sensitive K+ and Cl− channel pharmacological blockers, the steady shear stress-induced increase in cotransporter protein was virtually abolished. These results suggest that shear stress modulates the expression of the BAEC Na-K-Cl cotransporter by mechanisms that are dependent on flow-activated ion channels.
Desmin integrates the three-dimensional mechanical properties of muscles
Authors: Boriek Aladin M. , Capetanaki Y. , Hwang Willy , Officer Todd , Badshah Muffasir , Rodarte Joe , Tidball James G.
Published: December 2017

Striated muscle is a linear motor whose properties have been defined in terms of uniaxial structures. The question addressed here is what contribution is made to the properties of this motor by extramyofilament cytoskeletal structures that are not aligned in parallel with the myofilaments. This question arose from observations that transverse loads increase muscle force production in diaphragm but not in the hindlimb muscle, thereby indicating the presence of structures that couple longitudinal and transverse properties of diaphragmatic muscle. Furthermore, we find that the diaphragms of null mutants for the cytoskeletal protein desmin show 1) significant reductions in coupling between the longitudinal and transverse properties, indicating for the first time a role for a specific protein in integrating the three-dimensional mechanical properties of muscle, 2) significant reductions in the stiffness and viscoelasticity of muscle, and 3) significant increases in tetanic force production. Thus desmin serves a complex mechanical function in diaphragm muscle by contributing both to passive stiffness and viscoelasticity and to modulation of active force production in a three-dimensional structural network. Our finding changes the paradigm of force transmission among cells by placing our understanding of the function of the cytoskeleton in the context of the structural and mechanical complexity of muscles.
Hypertonicity-induced phosphorylation and nuclear localization of the transcription factor TonEBP
Authors: Dahl Stephen C. , Handler Joseph S. , Kwon H. Moo
Published: December 2017

The accumulation of compatible osmolytes during osmotic stress is observed in virtually all organisms. In mammals, the hypertonicity-induced expression of osmolyte transporters and synthetic enzymes is conferred by the presence of upstream tonicity-responsive enhancer (TonE) sequences. Recently, we described the cloning and initial characterization of TonE-binding protein (TonEBP), a transcription factor that translocates to the nucleus and associates with TonE sequences in a tonicity-dependent manner. We now report that hypertonicity induces an increase in TonEBP phosphorylation that temporally correlates with increased nuclear localization of the molecule. TonEBP phosphorylation is not affected by a number of kinase inhibitors, including the p38 inhibitor SB-203580. In addition, in vitro binding assays show that the association of TonEBP with TonE sequences is not affected by phosphorylation. Thus TonEBP phosphorylation is an early step in the response of cells to hypertonicity and may be required for nuclear import or retention.
Single rabbit stomach smooth muscle cell myosin heavy chain SMB expression and shortening velocity
Authors: Eddinger Thomas J. , Meer Daniel P.
Published: December 2017

Isolated single smooth muscle cells (SMCs) from different regions of the rabbit stomach were used to determine a possible correlation between unloaded shortening velocity and smooth muscle (SM) myosin heavy chain (MHC) S1 head isoform composition (SMA, no head insert; SMB, with head insert). α-Toxin-permeabilized isolated single cells were maximally activated to measure unloaded shortening velocity and subsequently used in an RT-PCR reaction to determine the SMA/SMB content of the same cell. SM MHC SMA and SMB isoforms are uniquely distributed in the stomach with cells from the fundic region expressing little SMB (38.1 ± 7.3% SMB; n = 16); cells from the antrum express primarily SMB (94.9 ± 1.0% SMB; n = 16). Mean fundic cell unloaded shortening velocity was 0.014 ± 0.002 cell lengths/s compared with 0.036 ± 0.002 for the antrum cells. Unloaded shortening velocity in these cells was significantly correlated with their percent SMB expression ( r 2 = 0.58). Resting cell length does not correlate with the percent SMB expression ( n = 32 cells). Previously published assays of purified or expressed SMA and SMB heavy meromyosin show a twofold difference in actin filament sliding speed in in vitro motility assays. Extrapolation of our data to 0–100% SMB would give a 10-fold range of shortening velocity, which is closer to the ∼20-fold range reported from various SM tissues. This suggests that mechanisms in addition to the MHC S1 head isoforms regulate shortening velocity.
Expression of extracellular calcium-sensing receptor in human osteoblastic MG-63 cell line
Authors: Yamaguchi Toru , Chattopadhyay Naibedya , Kifor Olga , Ye Chianping , Vassilev Peter M. , Sanders Jennifer L. , Brown Edward M.
Published: December 2017

We have previously shown the expression of the extracellular calcium (Cao 2+)-sensing receptor (CaR) in osteoblast-like cell lines, and others have documented its expression in sections of murine, bovine, and rat bone. The existence of the CaR in osteoblasts remains controversial, however, since some studies have failed to document its expression in the same osteoblast-like cell lines. The goals of the present study were twofold. 1) We sought to determine whether the CaR is expressed in the human osteoblast-like cell line, MG-63, which has recently been reported by others not to express this receptor. 2) We investigated whether the CaR, if present in MG-63 cells, is functionally active, since most previous studies have not proven the role of the CaR in mediating known actions of Cao 2+ on osteoblast-like cells. We used immunocytochemistry and Western blotting with the specific, affinity-purified anti-CaR antiserum 4637 as well as Northern blot analysis and RT-PCR using a riboprobe and PCR primers specific for the human CaR, respectively, to show readily detectable CaR protein and mRNA expression in MG-63 cells. Finally, we employed the patch-clamp technique to show that an elevation in Cao 2+ as well as the specific, allosteric CaR activator NPS R-467 (0.5 μM), but not its less active stereoisomer NPS S-467 (0.5 μM), activate an outward K+ channel in MG-63 cells, strongly suggesting that the CaR in MG-63 cells is not only expressed but is functionally active.
Control of microtubule assembly by extracellular matrix and externally applied strain
Authors: Putnam A. J. , Schultz K. , Mooney D. J.
Published: December 2017

A number of studies have suggested that externally applied mechanical forces and alterations in the intrinsic cell-extracellular matrix (ECM) force balance equivalently induce changes in cell phenotype. However, this possibility has never been directly tested. To test this hypothesis, we directly investigated the response of the microtubule (MT) cytoskeleton in smooth muscle cells to both mechanical signals and alterations in the ECM. A tensile force that resulted in a positive 10% step change in substrate strain increased MT mass by 34 ± 10% over static controls, independent of the cell adhesion ligand and tyrosine phosphorylation. Conversely, a compressive force that resulted in a negative 10% step change in substrate strain decreased MT mass by 40 ± 6% over static controls. In parallel, increasing the density of the ECM ligand fibronectin from 50 to 1,000 ng/cm2 in the absence of any applied force increased the amount of polymeric tubulin in the cell from 59 ± 11% to 81 ± 13% of the total cellular tubulin. These data are consistent with a model in which MT assembly is, in part, controlled by forces imposed on these structures, and they suggest a novel control point for MT assembly by altering the intrinsic cell-ECM force balance and applying external mechanical forces.
Differential effects of flavonoids on 3T3-L1 adipogenesis and lipolysis
Authors: Harmon Anne W. , Harp Joyce B.
Published: December 2017

Flavonoids, polyphenolic compounds that exist widely in plants, inhibit cell proliferation and increase cell differentiation in many cancerous and noncancerous cell lines. Because terminal differentiation of preadipocytes to adipocytes depends on proliferation of both pre- and postconfluent preadipocytes, we predicted that flavonoids would inhibit adipogenesis in the 3T3-L1 preadipocyte cell line. The flavonoids genistein and naringenin inhibited proliferation of preconfluent preadipocytes in a time- and dose-dependent manner. When added to 2-day postconfluent preadipocytes at the induction of differentiation, genistein inhibited mitotic clonal expansion, triglyceride accumulation, and peroxisome proliferator-activated receptor-γ expression, but naringenin had no effect. The antiadipogenic effect of genistein was not due to inhibition of insulin receptor subtrate-1 tyrosine phosphorylation. When added 3 days after induction of differentiation, neither flavonoid inhibited differentiation. In fully differentiated adipocytes, genistein increased basal and epinephrine-induced lipolysis, but naringenin had no significant effects. These data demonstrate that genistein and naringenin, despite structural similarity, have differential effects on adipogenesis and adipocyte lipid metabolism.
Regulation of SERCA Ca2+ pump expression by cytoplasmic [Ca2+] in vascular smooth muscle cells
Authors: Wu Kwan-Dun , Bungard David , Lytton Jonathan
Published: December 2017

Vascular smooth muscle cells (VSMC) express three isoforms of the sarcoplasmic or endoplasmic reticulum Ca2+-ATPase (SERCA) pump; SERCA2b predominates (91%), whereas SERCA2a (6%) and SERCA3 (3%) are present in much smaller amounts. Treatment with thapsigargin (Tg) or A-23187 increased the level of mRNA encoding SERCA2b four- to fivefold; SERCA3 increased about 10-fold, whereas SERCA2a was unchanged. Ca2+ chelation prevented the Tg-induced SERCA2b increase, whereas Ca2+ elevation itself increased SERCA2b expression. These responses were discordant with those of 78-kDa glucose-regulated protein/immunoglobulin-binding protein (grp78/BiP), an endoplasmic reticulum stress-response protein. SERCA2b mRNA elevation was much larger than could be accounted for by the observed increase in message stability. The induction of SERCA2b by Tg did not require protein synthesis, nor was it affected by inhibitors of calcineurin, protein kinase C, Ca2+/calmodulin-dependent protein kinase, or tyrosine protein kinases. Treatment with the nonselective protein kinase inhibitor H-7 prevented Tg-induced SERCA2b expression from occurring, whereas another nonselective inhibitor, staurosporine, was without effect. We conclude that changes in cytosolic Ca2+ control the expression of SERCA2b in VSMC via a mechanism involving a currently uncharacterized, H-7-sensitive but staurosporine-insensitive, protein kinase.
Hypoxia-activated ligand HAL-1/13 is lupus autoantigen Ku80 and mediates lymphoid cell adhesion in vitro
Authors: Lynch Eileen M. , Moreland Robert B. , Ginis Irene , Perrine Susan P. , Faller Douglas V.
Published: December 2017

Hypoxia is known to induce extravasation of lymphocytes and leukocytes during ischemic injury and increase the metastatic potential of malignant lymphoid cells. We have recently identified a new adhesion molecule, hypoxia-activated ligand-1/13 (HAL-1/13), that mediates the hypoxia-induced increases in lymphocyte and neutrophil adhesion to endothelium and hypoxia-mediated invasion of endothelial cell monolayers by tumor cells. In this report, we used expression cloning to identify this molecule as the lupus antigen and DNA-dependent protein kinase-associated nuclear protein, Ku80. The HAL-1/13-Ku80 antigen is present on the surface of leukemic and solid tumor cell lines, including T and B lymphomas, myeloid leukemias, neuroblastoma, rhabdomyosarcoma, and breast carcinoma cells. Transfection and ectopic expression of HAL-1/13-Ku80 on (murine) NIH/3T3 fibroblasts confers the ability of these normally nonadhesive cells to bind to a variety of human lymphoid cell lines. This adhesion can be specifically blocked by HAL-1/13 or Ku80-neutralizing antibodies. Loss of expression variants of these transfectants simultaneously lost their adhesive properties toward human lymphoid cells. Hypoxic exposure of tumor cell lines resulted in upregulation of HAL-1/13-Ku80 expression at the cell surface, mediated by redistribution of the antigen from the nucleus. These studies indicate that the HAL-1/13-Ku80 molecule may mediate, in part, the hypoxia-induced adhesion of lymphocytes, leukocytes, and tumor cells.
Insulin increases the turnover rate of Na+-K+-ATPase in human fibroblasts
Authors: Longo Nicola , Scaglia Fernando , Wang Yuhuan
Published: December 2017

Insulin stimulates K+ transport by the Na+-K+-ATPase in human fibroblasts. In other cell systems, this action represents an automatic response to increased intracellular [Na+] or results from translocation of transporters from an intracellular site to the plasma membrane. Here we evaluate whether these mechanisms are operative in human fibroblasts. Human fibroblasts expressed the α1 but not the α2 and α3 isoforms of Na+-K+-ATPase. Insulin increased the influx of Rb+, used to trace K+ entry, but did not modify the total intracellular content of K+, Rb+, and Na+ over a 3-h incubation period. Ouabain increased intracellular Na+ more rapidly in cells incubated with insulin, but this increase followed insulin stimulation of Rb+ transport. Bumetanide did not prevent the increased Na+ influx or stimulation of Na+-K+-ATPase. Stimulation of the Na+-K+- ATPase by insulin did not produce any measurable change in membrane potential. Insulin did not affect the affinity of the pump toward internal Na+ or the number of membrane-bound Na+-K+-ATPases, as assessed by ouabain binding. By contrast, insulin slightly increased the affinity of Na+-K+-ATPase toward ouabain. Phorbol esters did not mimic insulin action on Na+-K+-ATPase and inhibited, rather than stimulated, Rb+ transport. These results indicate that insulin increases the turnover rate of Na+-K+-ATPases of human fibroblasts without affecting their number on the plasma membrane or modifying their dependence on intracellular [Na+].