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Biomedical subjects

J Gao

Publications and source records attributed to J Gao.

At least 415 records · Page 23Linked to original sources
PubMed1994

Exercise induces rapid increases in GLUT4 expression, glucose transport capacity, and insulin-stimulated glycogen storage in muscle.

GLUT4 glucose transporter content and glucose transport capacity are closely correlated in skeletal muscle. In this study, we tested the hypothesis that a rapid increase in GLUT4 expression occurs as part of the early adaptive response of muscle to exercise and serves to enhance glycogen storage. Rats exercised by swimming had a approximately 2-fold increase in GLUT4 mRNA and a 50% increase in GLUT4 protein expression in epitrochlearis muscle 16 h after one prolonged exercise session. After a 2nd day of exercise, muscle GLUT4 protein was increased further to approximately 2-fold while there was no additional increase in GLUT4 mRNA. Muscle hexokinase activity also doubled in response to 2 days of exercise. Glucose transport activity maximally stimulated with insulin, contractions, or hypoxia was increased roughly in proportion to the adaptive increase in GLUT4 protein in epitrochlearis muscles. Treatment with insulin prior to subcellular fractionation of muscle resulted in a approximately 2-fold greater increase in GLUT4 content of a plasma membrane fraction in the 2-day swimmers than in controls. When epitrochlearis muscles were incubated with glucose and insulin, glycogen accumulation over 3 h was twice as great in muscles from 2-day swimmers as in control muscles. Our results show that a rapid increase in GLUT4 expression is an early adaptive response of muscle to exercise. This adaptation appears to be mediated by pretranslational mechanisms. We hypothesize that the physiological role of this adaptation is to enhance replenishment of muscle glycogen stores.

3-O-Methylglucose↗
PubMed1994

Identification of a higher molecular weight protein that shows apparent cross-reactivity with anti-p21ras monoclonal antibodies on western blots.

We have characterized the immune cross-reactivity of several commercially available monoclonal antibodies prepared against the p21ras proteins and used in Western blotting experiments against human tissue homogenates. Under optimal conditions, only two bands were observed on Western blots. One of these comigrated with control p21ras protein. A second protein of apparent mobility corresponding to approximately 54 kDa was also observed with all four monoclonal antibodies tested. Protein sequencing by automated Edman degradation indicates that the 54 kDa species corresponds to human immunoglobulin heavy chain. Under suboptimal conditions, another high molecular weight species of apparent mobility 65 kDa was also observed to cross-react with some of the monoclonal antibodies tested. This 65 kDa species was identified by protein sequencing as human serum albumin. Coomassie blue staining of SDS-polyacrylamide gels indicates that serum albumin is a major contaminant of many surgically obtained human tissue samples, while p21ras and immunoglobulin heavy chain are present at much lower concentrations. These results may be of significance when using monoclonal antibodies to determine p21ras levels of whole tissue homogenates by dot-blot, slot-blot or microplate assays.

Amino Acid Sequence↗
PubMed1994

Ferrylmyoglobin formation induced by acute magnesium deficiency in perfused rat heart causes cardiac failure.

The oxidation states of intracellular myoglobin and cytochrome oxidase aa3 were monitored by reflectance spectrophotometry in isolated perfused rat hearts subjected to an acutely magnesium deficient environment. After exposure to low extracellular [Mg2+]o (i.e., 0.3 mM) for 30 min, more than 80% of the oxymyoglobin converted to its deoxygenated form. The level of reduced cytochrome oxidase aa3 also increased about 80% in low [Mg2+]o. The deoxymyoglobin was converted further to a species identified as ferrylmyoglobin by its reaction with Na2S to form ferrous sulfmyoglobin which was optically visible. This process, set into motion by acute Mg deficiency, resulted from a direct accessibility of the exogenous peroxide to the cytosolic protein. The results suggest that a pathway leading to cardiac tissue damage, induced by magnesium deficiency, is probably involved in the generation of a ferrylmyoglobin radical which could be prevented by addition of ascorbate, which is known to be a one-electron reductant of this hypervalent form of myoglobin. In further studies, we also investigated whether addition of different concentrations of ascorbic acid (AA) to the perfusate could enhance myocardial function after exposure to low [Mg2+]o perfusion. Four concentrations of AA (0.5, 1, 5, 10 mM) were tested, and the results indicate that they exert their effects in a concentration-dependent manner; 1 mM AA was the most effective dose in improving aortic output in a Mg-deficient heart. Ferrylmyoglobin formation was found to be formed considerably before intracellular release of either creatine phosphokinase or lactic dehydrogenase. These studies may have wide implications as a new mechanism by which low extracellular Mg2+ can induce myocardial injury and subsequent cardiac failure.

Animals↗
PubMed1994

Developmental and environmental regulation of two ribosomal protein genes in tobacco.

Two cDNA clones, TSC29 and TSC40, were isolated from a cDNA library prepared from three-day-old tobacco cell suspension grown to early exponential stage. DNA sequence analyses and database searches revealed that the TSC29 transcript encodes a protein which is highly homologous to eukaryotic 60S ribosomal (r)-protein L25 and that the TSC40 product is homologous to rat 60S r-protein L34. Southern blot analysis showed that the putative r-protein genes are members of multigene families. Transcript levels of both genes were most abundant in three-day-old cell suspension and declined in older cultures. Transcripts were also present in plant vegetative and reproductive organs. However, for TSC40 in particular, the mRNA levels were lower in plant organs than in three-day-old cell suspension. Stems and roots exhibited higher expression than leaves and flowers, indicating that these clones are differentially regulated in various cell types. Both genes were expressed at low levels in mature seeds but transcript levels significantly increased after one day of germination, remained at a high level until day 4, and declined after day 5. In situ localization experiments with germinating seedlings revealed that the TSC29 transcript was preferentially localized in root tips, epidermis, and endosperm. Wounding increased the steady-state mRNA amounts of these r-protein genes, and 2,4-dichlorophenoxyacetic acid and benzyladenine further increased the transcript level.

Amino Acid Sequence↗
PubMed1994

The hydration and solvent polarization effects of nucleotide bases.

A combined Monte Carlo quantum mechanical and molecular mechanical (QM/MM) simulation method is used to determine the free energy of hydration and the solvent polarization effect for the nucleotide bases. In the present AM1/TIP3P model, the solute molecule is characterized by valence electrons and effective nucleus cores with Hartree-Fock molecular orbital theory incorporating a solute-solvent interaction Hamiltonian. It is found that polarization energy contributes up to 37%-61% of the total solute-solvent interaction for the systems considered. The computed free energies of hydration are compared with previous theoretical results.

Chemical Phenomena↗
PubMed1994

Mutations in transcript isoforms of the neurofibromatosis 2 gene in multiple human tumour types.

The neurofibromatosis 2 gene (NF2) has recently been isolated and predicted to encode a novel protein related to the moesin-ezrin-radixin family of cytoskeleton-associated proteins. Here we describe a novel isoform of the NF2 transcript that shows differential tissue expression and encodes a modified C terminus of the predicted protein. Mutations affecting both isoforms of the NF2 transcript were detected in multiple tumour types including melanoma and breast carcinoma. These findings provide evidence that alterations in the NF2 transcript occur not only in the hereditary brain neoplasms typically associated with NF2, but also as somatic mutations in their sporadic counterparts and in seemingly unrelated tumour types. The NF2 gene may thus constitute a tumour suppressor gene of more general importance in tumorigenesis.

Alternative Splicing↗
PubMed1994

Contraction-induced increase in muscle insulin sensitivity: requirement for a serum factor.

The insulin sensitivity of glucose transport is enhanced in skeletal muscle after a bout of exercise. In a previous study, stimulation of washed muscles to contract in vitro, in contrast to exercise, did not result in an increase in insulin sensitivity. The purpose of the present study was to explain this apparent discrepancy. We found that, although rat epitrochlearis muscles stimulated to contract in vitro after 15 min of incubation in Krebs-Henseleit buffer did not develop increased insulin sensitivity, muscles stimulated to contract immediately after being dissected showed a small but significant enhancement of the stimulation of 3-O-methyl-D-glucose transport by 30 microU/ml insulin. Furthermore, muscles stimulated to contract in situ and then allowed to recover in vitro showed as large an increase in insulin sensitivity as that which occurs after a bout of swimming. To follow up these findings suggesting involvement of a humoral factor, we incubated epitrochlearis muscles in serum before and during contractile activity in vitro. Epitrochlearis muscle insulin sensitivity was enhanced to as great an extent after in vitro contractile activity in serum as after swimming. Experiments involving charcoal treatment, ultrafiltration, or trypsin digestion provided evidence that the serum factor that interacts with contractions to enhance insulin sensitivity is a protein.

Animals↗
PubMed1994

Effects of acute running exercise on whole body insulin action in obese male SHHF/Mcc-facp rats.

This study utilized the obese male spontaneously hypertensive heart failure rat (SHHF/Mcc-facp), which has metabolic features very similar to human non-insulin-dependent diabetes mellitus. The purpose of this study was to assess the insulin sensitivity and responsiveness of whole body glucose disposal and insulin suppressability of hepatic glucose production with use of the euglycemic-hyperinsulinemic clamp procedure in 12- to 15-wk-old SHHF/Mcc-facp rats at rest (OS) and 2.5 h after a single session of acute exercise (OE). Lean male SHHF/Mcc-facp rats were sedentary (LS) control animals. At least three clamps producing different insulin-stimulated responses were performed on each animal in a randomized order. At this age the obese animals are normotensive and have not developed congestive heart failure. Compared with LS, OS were significantly hyperglycemic and hyperinsulinemic and insulin sensitivity and responsiveness of whole body glucose uptake and insulin suppressability of hepatic glucose production were significantly decreased. Compared with LS and OS, acute exercise significantly decreased resting plasma glucose but did not alter plasma insulin. Compared with OS, acute exercise significantly increased the insulin responsiveness of whole body glucose disposal but did not affect the sensitivity of whole body glucose disposal or insulin suppressability of hepatic glucose production. Compared with LS, however, acute exercise did not "normalize" the insulin responsiveness of whole body glucose disposal. Thus a single acute exercise session improves but does not normalize whole body insulin resistance in the SHHF/Mcc-facp rat.

Animals↗
PubMed1994

Additive effect of contractions and insulin on GLUT-4 translocation into the sarcolemma.

The maximal effects of insulin and muscle contractions on glucose transport are additive. GLUT-4 is the major glucose transporter isoform expressed in skeletal muscle. Muscle contraction and insulin each induce translocation of GLUT-4 from intracellular sites into the plasma membrane. The purpose of this study was to test the hypothesis that the incremental effect of contractions and insulin on glucose transport is mediated by additivity of the maximal effects of these stimuli on GLUT-4 translocation into the sarcolemma. Anesthetized rats were given insulin by intravenous infusion to raise plasma insulin to 2,635 +/- 638 microU/ml. The gastrocnemius-plantaris-soleus group was stimulated to contract via the sciatic nerve by using a protocol that maximally activates glucose transport. After treatment with insulin, contractions, or insulin plus contractions or no treatment, the gastrocnemius-plantaris-soleus muscle group was dissected out and was subjected to subcellular fractionation to separate the plasma membrane and intracellular membrane fractions. Insulin induced a 70% increase and contractions induced a 113% increase in the GLUT-4 content of the plasma membrane fraction. The effects of insulin and contractions were additive, as evidenced by a 185% increase in the GLUT-4 content of the sarcolemmal fraction. This finding provides evidence that the incremental effect of maximally effective insulin and contractile stimuli on glucose transport is mediated by additivity of their effects on GLUT-4 translocation into the sarcolemma.

Animals↗
PubMed1994

[Effect of LDL on human mesangial cell proliferation].

Hyperlipidemia is one of the main features of nephrotic syndrome (NS), which has been reported to be important in the pathogenesis of mesangial cell proliferation. In an attempt to understand if LDL of the NS patients is more nephrotoxic on the development of mesangial cell proliferation, serum lipoprotein composition of normal controls, patients of NS untreated and treated with steroid drugs were measured, moreover, the influence of LDL from each group of patients on the proliferation of human mesangial cell (HMC) were observed. Lipoprotein composition was measured by enzymic methods. LDL was prepared by ultracentrifugation and used within three weeks. HMC was cultured and identified by classical methods, mesangial cell proliferation was observed by 3H-TdR incorporation according to the dose of LDL from 20-1000 micrograms/ml and time from 24 hours to 72 hours. Our results indicated that: 1. Both the NS patients untreated and treated with steroid drugs showed hypercholesterolemia and hypertriglyceride, serum low-density lipoprotein cholesterol (LDL-ch) concentration were higher in these patients than in the normal control group but there was no significant difference between NS untreated and treated groups. 2. LDL from normal controls or NS patients had biphasic effect on HMC proliferation. Low concentration stimulated HMC proliferation in concentration dependent and time-dependent manner, where as high concentration inhibited HMC proliferation. There was no significant difference on the effect of HMC proliferation between NS untreated and treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

The attachments of the rabbit medial meniscus. A morphological investigation using image analysis and immunohistochemistry.

In the search for a suitable experimental model the rabbit has increasingly been used for investigations on the meniscus. The present study focused on the morphology and innervation of the anterior and posterior medial meniscal attachments in adolescent and adult rabbits in comparison with man. Grossly, the posterior attachment has a similar anatomical position as in man, but the anterior is inserted more anteriorly and more laterally, with a long ligament-like structure between the osseous insertion and the meniscal horn. As in man, the attachment resembles a ligamentous insertion and contains zones of uncalcified and calcified fibrocartilage and subchondral bone. The proportion of the calcified cartilaginous zone in the attachment increases during maturation as in articular cartilage. Nerve fibres were found not only at the horns but also in the uncalcified and calcified fibrocartilaginous zones and the underlying bone. The differences between rabbit and human menisci should be borne in mind when interpreting data from animal experiments.

Animals↗
PubMed1994

[Endothelial cell injury and changes in anti-coagulation properties induced by burn serum in vitro].

The purpose of this study is to clarify the effect of burn rabbit serum on the function and structure of endothelial cells in vitro. Morphological study (inverted microscopy, scanning electron microscopy), and determinations of LDH, 6-keto-PGF1 alpha and tissue-type plasminogen activator in the culture medium, changes in the ability of anti-adhesion of platelet to endothelial cells and anti-aggregation property of platelet, etc. were performed. The main results and conclusions were as follows: (1) Rabbit serum obtained in the early stage exerted obvious toxic effects on endothelial cells, functional changes appeared earlier than structural, and in the later changes in intercellular junction and cellular surface appeared earlier; (2) Burn rabbit serum significantly reduced the ability of anti-adhesion of platelet to endothelial cell and anti-aggregation property of platelet, and it might be the primary cause of local micro-thrombosis; (3) Because of the destruction of endothelial surface, the ability of fibrinolysis of endothelial cells was reduced. The activity of tPA might be inhibited b PAI-1, although the content of tPA in the culture medium seemed to be increased after endothelial cell injury.

Animals↗
PubMed1994

[Electron microscopic studies of the endoplasmic reticulum in whole--mount cultured human nasopharyngeal carcinoma cell line].

The endoplasmic reticulum system (ER) in whole-mount human nasopharyngeal carcinoma parent cell line (CNE-2Z) and its variants L2, H2, L4 was observed using potassium permangnate as a fixtive. In lamellapodia and labopodia, the ER was arranged as a nest structure, but it usually formed lines of straight tubules in the filopodia. The results suggested that there may be some relationship between the ER and the functional activities of pseudopodia. No significant difference of ER was found yet in morphology, structure, quantities and distribution between CNE-2Z cells and its variants.

Carcinoma, Squamous Cell↗