RESUMEN
INTRODUCTION: The Exeter Trauma Stem (ETS) has been recommended by National Institute of Clinical Excellence (NICE) guidelines in the United Kingdom as a proven, cemented stem. A single laboratory study in the literature has raised possible concerns about the polished finish of the ETS and subsequent potential for accelerated loosening although there is little clinical evidence to support or refute this. METHODS: The aim of this study was to assess clinical outcomes of the ETS at a minimum of five years post implantation. Primary outcomes were radiological loosening at a minimum of five years along with survivorship of the implant. Patient demographics were prospectively collected and followed up. RESULTS: 218 ETS's (in 214 patients) were implanted from June 2002 until August 2008 in a single centre by a wide variety of surgeons of differing grades. Of these, 16 underwent revision surgery for fracture (2), dislocation (3), infection (1) and acetabular erosion (10) but there were no revisions for aseptic loosening of the implant. There were 64.0% (137/214) patients that had died by the time of this study. Of the remaining patients, 90 had radiographs of their hips at a minimum of 5 years with 36 of these at a minimum of 7 years post implantation. None of these had evidence of loosening. CONCLUSION: The ETS is a robust and suitable stem for implantation in patients with hip fractures. There are no clinical suspicions or increased rates of loosening with the ETS in our study. The concerns about surface finish are not borne out in our clinical study which shows no evidence of loosening at a minimum of five years post operation. It confers many advantages including ease of revision and it should continue to be used as per NICE guidelines.
Asunto(s)
Artroplastia de Reemplazo de Cadera , Cementación , Fracturas de Cadera/cirugía , Prótesis de Cadera , Radiografía , Reoperación/estadística & datos numéricos , Actividades Cotidianas , Anciano , Anciano de 80 o más Años , Artroplastia de Reemplazo de Cadera/efectos adversos , Artroplastia de Reemplazo de Cadera/estadística & datos numéricos , Cementos para Huesos , Femenino , Estudios de Seguimiento , Fracturas de Cadera/diagnóstico por imagen , Fracturas de Cadera/fisiopatología , Humanos , Masculino , Persona de Mediana Edad , Diseño de Prótesis , Falla de Prótesis , Estudios Retrospectivos , Resultado del Tratamiento , Reino Unido/epidemiologíaRESUMEN
Only two tumor suppressor gene loci, one on 3p25 and the MEN1 gene on 11q13, have thus far been implicated in the pathogenesis of sporadic human pancreatic endocrine tumors (PETs). A genome-wide allelotyping study of 28 human PETs was undertaken to identify other potential tumor suppressor gene loci. In addition to those on chromosomes 3p and 11q, frequent allelic deletions were identified on 3q (32%), 11p (36%), 16p (36%), and 22q (29%). Finer deletion mapping studies localized the smallest regions of common deletion to 3q27, 11p13, and 16p12.3-13.11. Potential candidate genes at these loci include WT1 (11p13), TSC2 (16p13), and NF2 (22q12), but no known tumor suppressor gene localizes to 3q27. The mean fractional allelic loss among these human PETs is 0.126, and no correlation was observed between allelic loss and clinical parameters, including age, sex, hormonal subtype, and disease stage. These findings highlight novel locations of tumor suppressor gene loci that contribute to the pathogenesis of human PETs, and several of these on 3p, 3q, and 22q are syntenic with loci on mouse chromosomes 9 and 16 that are implicated in a murine transgenic model of PETs.
Asunto(s)
Mapeo Cromosómico , Genes Supresores de Tumor , Neoplasias Pancreáticas/genética , Adulto , Anciano , Anciano de 80 o más Años , Alelos , Cromosomas Humanos Par 11/genética , Cromosomas Humanos Par 16/genética , Cromosomas Humanos Par 22/genética , Femenino , Eliminación de Gen , Marcadores Genéticos , Genotipo , Humanos , Masculino , Persona de Mediana Edad , Neoplasias Pancreáticas/patologíaRESUMEN
The human erythrocyte D-glucose transporter is an integral membrane glycoprotein with an heterogeneous molecular mass spanning a range 45-70 kDa. The protein structure of the transporter was investigated by photoaffinity labeling with [3H]cytochalasin B and fractionating the labeled transporter according to molecular mass by preparative SDS-polyacrylamide gel electrophoresis. Each fraction was digested with either papain or S. aureus V8 proteinase, and the labeled proteolytically derived peptide fragments were compared by SDS polyacrylamide gel electrophoresis. Papain digestion yielded two major peptide fragments, of approx. molecular mass 39 +/- 2 and 22 +/- 2 kDa; treatment with V8 proteinase resulted in two fragments, with mass of 24 +/- 2 and 15 +/- 2. Proteolysis of each transporter fraction produced the same pattern of labeled peptide fragments, irrespective of the molecular mass of the original fractions. The binding characteristics of [3H]cytochalasin-B-labeled transporter to Ricinis communis agglutinin lectin was examined for each transporter molecular mass fraction. It was found that higher-molecular-mass fractions of intact transporter had a 2-fold greater affinity for the lectin than lower-molecular-mass fractions (i.e., 67 kDa greater than 45 kDa fraction). However, proteolytically derived labeled peptide fragments from each fraction had minimal affinity for the lectin. These results suggest that the labeled peptide fragments have been separated from the glycosylated regions of the parent transporter protein. The present findings indicate that, although transporter proteins have an apparently heterogeneous molecular mass, some regions of the protein share a common peptide. Furthermore, the glycosylated regions appear to be located some distance from the [3H]cytochalasin-B-labeled site(s).
Asunto(s)
Membrana Eritrocítica/análisis , Proteínas de Transporte de Monosacáridos/análisis , Lectinas de Plantas , Serina Endopeptidasas , Marcadores de Afinidad , Sitios de Unión , Quimotripsina , Citocalasina B , Endopeptidasas , Humanos , Lectinas , Papaína , Fragmentos de Péptidos/análisis , TripsinaRESUMEN
The effect of transformation on hexose and amino acid transport has been studied using whole cells and membrane vesicles of chicken embryo fibroblasts infected with the temperature-sensitive mutant of the Rous sarcoma virus, TS-68. In whole cells, TS-68-infected chicken embryo fibroblasts cultured at the permissive temperature (37 degrees C) had a 2-fold higher rate of 2-deoxy-D-glucose uptake than the same cells cultured at the non-permissive temperature (41 degrees C). However, both the non-transformed and transformed cells had comparable rates of alpha-aminoisobutyric acid transport. Membrane vesicles, isolated from TS-68-infected chicken embryo fibroblasts cultured at 41 degrees C or 37 degrees C, displayed carrier-mediated, intravesicular uptake of D-glucose and alpha-aminoisobutyric acid. Membrane vesicles from TS-68-infected chicken embryo fibroblasts cultured at 37 degrees C had an approx. 50% greater initial rate of stereospecific hexose uptake than the membrane vesicles from fibroblasts cultured at 41 degrees C. The two types of membrane vesicle had similar uptake rates of alpha-aminoisobutyric acid. The results of hexose and amino acid uptake by the membrane vesicles correlated well with those observed with the whole cells. Km values for stereospecific D-glucose uptake by the membrane vesicles from TS-68-infected chicken embryo fibroblasts cultured at 41 and 37 degrees C were similar, but the V value was greater for the membrane vesicles from TS-68-infected cells cultured at 37 degrees C. Cytochalasin B competitively inhibited stereospecific hexose uptake in both types of membrane vesicle. These findings suggest that the membrane vesicles retained many of the features of hexose and amino acid transport observed in whole cells, and that the increased rate of hexose transport seen in the virally-transformed chicken embryo fibroblasts was due to an increase in the number or availability of hexose carriers.
Asunto(s)
Ácidos Aminoisobutíricos/metabolismo , Virus del Sarcoma Aviar/metabolismo , Transformación Celular Viral , Galactosa/metabolismo , Glucosa/metabolismo , Aminoácidos/farmacología , Animales , Transporte Biológico/efectos de los fármacos , Transporte Biológico Activo/efectos de los fármacos , Células Cultivadas , Embrión de Pollo , Citocalasina B/farmacología , Fibroblastos/metabolismo , Hexosas/farmacología , CinéticaRESUMEN
PURPOSE: The aim of the study is to show, on an MRI scan, that the posterior border of the anterior horn of the lateral meniscus (AHLM) could guide tibial tunnel position in the sagittal plane and provide anatomical graft position. METHOD: One hundred MRI scans were analysed with normal cruciate ligaments and no evidence of meniscal injury. We measured the distance between the posterior border of the AHLM and the midpoint of the ACL by superimposing sagittal images. RESULTS: The mean distance between the posterior border of the AHLM and the ACL midpoint was -0.1mm (i.e. 0.1mm posterior to the ACL midpoint). The range was 5mm to -4.6mm. The median value was 0.0mm. 95% confidence interval was from -0.5 to 0.3mm. A normal, parametric distribution was observed and Intra- and inter-observer variability showed significant correlation (p<0.05) using Pearsons Correlation test (intra-observer) and Interclass correlation (inter-observer). CONCLUSION: Using the posterior border of the AHLM is a reproducible and anatomical marker for the midpoint of the ACL footprint in the majority of cases. It can be used intra-operatively as a guide for tibial tunnel insertion and graft placement allowing anatomical reconstruction. There will inevitably be some anatomical variation. Pre-operative MRI assessment of the relationship between AHLM and ACL footprint is advised to improve surgical planning. LEVEL OF EVIDENCE: Level 4.
RESUMEN
Gastrin transcription in islet cells is activated by a cis-regulatory sequence containing a binding site for the yeast transcription factor RAP1. The DNA-protein interactions between RAP1 protein and the gastrin DNA element determined by methylation interference assays are identical to those of RAP1 and yeast genes. Point mutations in the gastrin RAP1 binding site, which abolished RAP1 binding, decreased transcriptional activation by this sequence. Islet cells revealed a DNA binding protein with RAP1-like binding specificity. These findings support the conclusion that gastrin transcription is activated in mammalian cells by a RAP1-like transcription factor.
Asunto(s)
Proteínas de Unión al GTP/metabolismo , Gastrinas/genética , Islotes Pancreáticos/metabolismo , Regiones Promotoras Genéticas , Factores de Transcripción/metabolismo , Transcripción Genética , Animales , Secuencia de Bases , Línea Celular , Cricetinae , ADN/metabolismo , Humanos , Islotes Pancreáticos/citología , Datos de Secuencia Molecular , Ratas , Homología de Secuencia de Ácido Nucleico , Células Tumorales Cultivadas , Proteínas de Unión al GTP rapRESUMEN
Photoaffinity labeling with [3H]cytochalasin B detects two D-glucose-sensitive proteins in the chicken embryo fibroblast (CEF) plasma membrane, which accumulate under conditions of glucose starvation and are probably involved in the glucose transport system (Pessin, J.E., et al. (1982) Proc. Natl. Acad. Sci. U.S. 79, 2286-2290). The two labeled components, designated as peak I (Mr 45,000) and II (Mr 52,000) components, were separated by preparative gel electrophoresis in the presence of sodium dodecyl sulfate. The fractions were digested with S. aureus V8 or papain, and the radioactive products were analyzed by one-dimensional gel electrophoresis. The peptide maps showed that they have different peptide structures. Peptide maps of authentic actin, a possible contaminant of the peak I fractions, were quite different from those of the peak I component. Rous sarcoma virus-transformed CEF have two components similar as to apparent molecular size and peptide maps to those present in glucose-starved cells. The peak I and II components show minimal affinity to agarose-bound Ricinus communis agglutinin which binds the human erythrocyte glucose transporter quite well. The peak II component was more susceptible to proteolysis than the peak I one or the human erythrocyte glucose transporter. However, the peptide maps of the peak II component were similar to those of the human erythrocyte glucose transporter.
Asunto(s)
Fibroblastos/análisis , Proteínas HSP70 de Choque Térmico , Proteínas de la Membrana/aislamiento & purificación , Actinas/análisis , Marcadores de Afinidad , Animales , Membrana Celular/análisis , Embrión de Pollo , Reactivos de Enlaces Cruzados , Citocalasina B/metabolismo , Eritrocitos/análisis , Humanos , Proteínas de Transporte de Monosacáridos/análisis , Músculos/análisis , Fragmentos de Péptidos/análisis , Péptido Hidrolasas , Fotoquímica , ConejosRESUMEN
Tissue from a vasoactive intestinal peptide (VIP)-secreting human tumor has been used to establish and characterize human neuroendocrine primary cell cultures from which permanent, clone-derived cell lines have been established. Viable cells were obtained by enzymatic and mechanical dissociation of freshly resected pancreatic islet tumor and hepatic metastatic tumor tissues. Aliquots of tumor cells were established ex vivo under culture conditions including porous substrata coated with type IV collagen and laminin and a low serum, hormonally defined culture medium. The small (<10 microm) rounded, grape-like cells had a very slow growth rate of doubling times estimated at several weeks or more. After several passages, morphologically uniform cells were derived that strongly expressed neuroendocrine markers of synaptophysin and synaptobrevin. Although chromogranin A and VIP had somewhat weaker expression, both demonstrated phorbol ester-stimulated secretion. The morphologic and secretory properties were maintained by the cells for nearly 2 years in culture. The establishment of this novel VIP-secreting human neuroendocrine cell line (HuNET) makes available a culture model with which to study a transformed version of this pancreatic islet cell type and offers approaches by which to establish islet tumor cell lines.
Asunto(s)
Carcinoma de Células de los Islotes Pancreáticos/metabolismo , Neoplasias Hepáticas/metabolismo , Neoplasias Pancreáticas/metabolismo , Péptido Intestinal Vasoactivo/metabolismo , Adulto , Carcinoma de Células de los Islotes Pancreáticos/secundario , Separación Celular , Cromogranina A , Cromograninas/metabolismo , Criopreservación , Técnica del Anticuerpo Fluorescente Indirecta , Humanos , Técnicas para Inmunoenzimas , Neoplasias Hepáticas/secundario , Masculino , Neoplasias Pancreáticas/patología , Sinaptofisina/metabolismo , Células Tumorales CultivadasRESUMEN
There is a need to better understand how psychosocial factors influence regimen adherence behavior. Therefore, the purpose of this study was to assess the ability of internal diabetes locus of control and social support to predict adherence to a weight-control regimen among persons with non-insulin-dependent diabetes mellitus (NIDDM). A community-based sample of 465 patients with NIDDM was interviewed. Regression analyses revealed that internal locus of control and social support were modest but statistically significant predictors. Correlation analyses showed that internal locus of control was not related to weight control in the high social support group. In the low social support group, a stronger internal locus of control was not associated with weight management. The ways in which internal locus of control and social support work together were not clear. The findings suggest that these two factors are advantageous for promoting regimen adherence.
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Diabetes Mellitus Tipo 2/rehabilitación , Control Interno-Externo , Cooperación del Paciente , Apoyo Social , Adulto , Anciano , Anciano de 80 o más Años , Diabetes Mellitus Tipo 2/psicología , Femenino , Humanos , Masculino , Persona de Mediana Edad , Valor Predictivo de las Pruebas , Análisis de Regresión , Factores Socioeconómicos , Encuestas y CuestionariosAsunto(s)
Cifosis/prevención & control , Complicaciones Posoperatorias/prevención & control , Enfermedades de la Columna Vertebral/cirugía , Fusión Vertebral/métodos , Adulto , Factores de Edad , Humanos , Incidencia , Cifosis/epidemiología , Cifosis/etiología , Tornillos Pediculares , Complicaciones Posoperatorias/epidemiología , Complicaciones Posoperatorias/etiología , Reoperación , Factores de Riesgo , Fusión Vertebral/efectos adversos , Fusión Vertebral/instrumentaciónAsunto(s)
Dolor/diagnóstico , Abdomen , Adulto , Femenino , Humanos , Persona de Mediana Edad , Pacientes , TóraxAsunto(s)
Neoplasias Pancreáticas/diagnóstico , Vipoma/diagnóstico , Adulto , Humanos , Neoplasias Hepáticas/diagnóstico , Neoplasias Hepáticas/secundario , Imagen por Resonancia Magnética , Masculino , Células Neoplásicas Circulantes , Neoplasias Pancreáticas/patología , Péptido Intestinal Vasoactivo/sangre , Vipoma/secundarioRESUMEN
Expression of gastrin, a gut hormone and growth factor, has tissue-specific transcriptional regulation and can be induced in some tumors. Previous studies have shown that a CACC cis-regulatory element is important for transcriptional activation in pancreatic insulinoma cells. To identify CACC-binding proteins, a lambda phage cDNA library derived from a rat insulinoma cell line, RIN 38A, was screened by a Southwestern method. A novel member of the Cys2-His2 zinc finger gene family was cloned and designated RIN ZF, having a cDNA sequence of 3.8 kilobases. One full-length and a shorter splice variant were sequenced and had predicted protein masses of 91.6 and 88.7 kDa. Expression of both splice forms were ubiquitous in fetal and adult rat tissues. Recombinant RIN ZF protein exhibited sequence-specific binding to the gastrin CACC element in a gel mobility shift assay. In transient transfections, both splice variants appeared to have only weak activating effects on gastrin-luciferase reporter gene transcription. Furthermore, RIN ZF coexpression with Sp1 appeared to block the strongly activating effects of Sp1 mediated through the CACC element. These findings suggest that a novel set of zinc finger proteins may help regulate gastrin gene expression by interfering with Sp1 transactivation.
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Proteínas de Unión al ADN/genética , Gastrinas/genética , Regiones Promotoras Genéticas , Dedos de Zinc/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Clonación Molecular , Genes Reporteros , Insulinoma/genética , Datos de Secuencia Molecular , Sistemas de Lectura Abierta , Reacción en Cadena de la Polimerasa , ARN Mensajero/metabolismo , Ratas , Células Tumorales CultivadasRESUMEN
The availability of coherent sources producing usable amounts of power in the optical frequency range has stimulated considerable research in optical communications. Devices such as oscillators, modulators, detectors, and ancillary apparatus having desirable characteristics exist and are being used to design and build prototype terminals. Two possible media are being studied and means are being sought to improve their performance. They are 1) through-the atmosphere propagation and 2) enclosed media with appropriate focusing and directing elements. Experimental optical transmission systems can readily be assembled with information capacities in a single RF channel comparable to those of microwave radio or millimeter waveguide. Such optical systems are not yet competitive for high reliability common carrier service because 1) long-distance transmission techniques of adequate reliability have not yet been advanced, and 2) optical repeater components are not yet competitive with their lower frequency counterparts. Some features characteristic of optical transmission systems are reviewed in this paper, along with a brief indication of the state-of-the-art for major components.
RESUMEN
N-myristoylated viral polypeptide mu 1 was produced in COS cells transfected with a transient expression vector containing a DNA copy of the reovirus M2 gene. The mu 1 product was specifically cleaved to polypeptide mu 1C in cells that were cotransfected with the reovirus S4 gene and that expressed polypeptide sigma 3. Studies with site-specific mutants of the M2 gene demonstrated that conversion of mu 1 to mu 1C was dependent on myristoylation and the presence of the proteolytic cleavage sequence asparagine 42-proline 43 in mu 1, as well as on the presence of polypeptide sigma 3. The mu 1C product and polypeptide sigma 3 formed complexes that were immunoprecipitated by sigma 3-directed antibody, and a myristoylation-negative M2 double mutant, G2A-N42T, yielded mu 1 that did not undergo cleavage to mu 1C or bind sigma 3. However, the N42T single mutant did form immunoprecipitable complexes with sigma 3, indicating that binding can occur in the absence of cleavage. Polypeptide sigma 3 alternatively can bind double-stranded RNA and in COS cells stimulates translation of reporter chloramphenicol acetyltransferase mRNA translation, presumably by blocking double-stranded RNA-mediated activation of the eukaryotic initiation factor 2 alpha subunit kinase which inhibits the initiation of protein synthesis. Consistent with these observations and with the formation of mu 1C-sigma 3 complexes, coexpression of M2 with S4 DNA prevented the translational stimulatory effect of polypeptide sigma 3.
Asunto(s)
Proteínas de la Cápside , Cápside/metabolismo , Ácidos Mirísticos/metabolismo , Proteínas de Unión al ARN , Reoviridae/genética , Proteínas Virales/metabolismo , Cápside/genética , Línea Celular , Cloranfenicol O-Acetiltransferasa/genética , Clonación Molecular , Mutagénesis Sitio-Dirigida , Pruebas de Precipitina , Procesamiento Proteico-Postraduccional , Reoviridae/metabolismo , Transfección , Proteínas Virales/genéticaRESUMEN
The regulation of hexose transporters of cultured fibroblasts was investigated by exposing chicken embryo fibroblasts (CEF) to hypertonic culture medium, a condition known to enhance hexose transport activity. The effects of hypertonicity and the role of protein synthesis were examined with CEF in the basal (glucose fed) and transport enhanced (glucose starved) states. Glucose-fed CEF exposed to hypertonic conditions developed four-fold enhancement of hexose transport activity within 4 hrs; this declined in the following 20 hrs to a level slightly higher than the fed control. Protein synthesis was required in part for this effect, since the presence of cycloheximide during hypertonic exposure of fed CEF blocked the increase in of transport by almost 50%. Although the increased transport produced by glucose starvation was not further enhanced by hypertonicity, hypertonic treatment of starved CEF during glucose refeeding largely prevented the loss of transport activity to the basal, fed state. The hypertonic effects were concentration dependent (240mOsm optimal) and could be elicited with NaCl, KCl, or sucrose. Hypertonic treatment typically led to a greater than 50% decline in the incorporation of [3H]leucine into acid-insoluble fractions. The changes in transport were evident at the plasma membrane level, and studies of membrane vesicles prepared from hypertonically treated fed CEF showed a doubling of both [3H]cytochalasin B binding and the Vmax of D-glucose transport. These findings indicate that exposure of CEF to hypertonic conditions has some effects similar to those produced by glucose starvation and suggest that protein synthesis is to some extent involved in the regulation of hexose transporters in CEF.
Asunto(s)
Fibroblastos/metabolismo , Soluciones Hipertónicas , Proteínas de Transporte de Monosacáridos/metabolismo , Animales , Embrión de Pollo , Medios de CultivoRESUMEN
The gastrin gene is transiently expressed in fetal pancreatic islets during islet neogenesis but then switched off after birth when islet cells become fully differentiated. Previous studies identified a cis-regulatory sequence between -109 and -75 in the human gastrin promoter which binds islet cell-specific activators and a nonspecific repressor and thus may act as a molecular switch. The present study identified another cis-regulatory sequence (-163ACACTAAATGAAAGGGCGGGGCAG-140) which bound two islet nuclear proteins in a mutually exclusive manner, as defined by gel shift competition, methylation interference, and DNase I foot-printing assays. The general transactivator Sp1 recognized the downstream GGGCGGGG sequence, but Sp1 binding was prevented when another islet factor bound to the adjacent AT-rich sequence (CTAAATGA). This gastrin AT-rich element is nearly identical to the binding site (ATAAATGA) for the islet-specific transcription factor beta TF-1. However, the gastrin AT-binding factor appeared to differ from beta TF-1 in its gel mobility shift pattern. Transfections of rat insulinoma cells revealed that mutations which blocked binding to the AT-rich element but allowed Sp1 binding up-regulated transcriptional activity. These results suggest that the gastrin AT-binding factor blocks transactivation by Sp1 and may have a role in the repression of gastrin transcription seen at the end of islet differentiation.
Asunto(s)
Gastrinas/genética , Regulación de la Expresión Génica , Islotes Pancreáticos/metabolismo , Factor de Transcripción Sp1/metabolismo , Adenina , Animales , Secuencia de Bases , Humanos , Insulinoma/genética , Islotes Pancreáticos/embriología , Datos de Secuencia Molecular , Mutagénesis , Oligodesoxirribonucleótidos , Regiones Promotoras Genéticas , Unión Proteica , Ratas , Secuencias Reguladoras de Ácidos Nucleicos , Timina , Transcripción Genética , Células Tumorales CultivadasRESUMEN
Regulation of hexose transport was investigated in chicken embryo fibroblasts (CEF) which develop 4- to 8-fold enhanced hexose transport activity during glucose starvation. The presence of cycloheximide in low (0.5 micrograms/ml) concentrations during starvation largely blocked the enhancement of transport activity. Glucose refeeding of CEF in the starvation state led to a decline in transport to the basal level. This decline was either potentiated or blocked by the presence of cycloheximide in low or high (50 micrograms/ml) concentrations, respectively. Exposure of CEF in the fed state to low concentrations of cycloheximide resulted in a 70% decrease of transport within 6 h, whereas exposure to high concentrations of cycloheximide led to only a modest loss (35% decrease). In the glucose-starved state, CEF had no significant decline of transport when exposed to cycloheximide at either high or low concentrations. The uptake of 3-O-methylglucose by fed, starved, or cycloheximide-treated CEF correlated closely with D-glucose transport activity and [3H]cytochalasin B binding by plasma membranes prepared from CEF exposed to the same conditions. Hexose transport activity of CEF seems to largely depend on the number of functioning carriers in the plasma membrane, which apparently reflect the balance between carrier synthesis and inactivation. These two processes require protein synthesis, but are differentially sensitive to the effects of cycloheximide, such that low concentrations of cycloheximide appear to block primarily synthesis while high concentrations block both processes. Furthermore, during starvation the enhancement of transport appears largely due to decreased carrier inactivation in the face of continued carrier synthesis.
Asunto(s)
Proteínas Portadoras/metabolismo , Fibroblastos/metabolismo , Glucosa/metabolismo , Biosíntesis de Proteínas , Animales , Transporte Biológico Activo/efectos de los fármacos , Embrión de Pollo , Cicloheximida/farmacología , Citocalasina B/metabolismo , Relación Dosis-Respuesta a Droga , Fibroblastos/efectos de los fármacos , CinéticaRESUMEN
Chicken embryo fibroblasts (CEF) when exposed to glucose-deficient culture medium developed 4- to 10-fold enhanced hexose transport activity within a few hours. Plasma membrane fractions prepared from starved and fed CEF revealed that starved cell membranes had a threefold greater glucose transport activity and [3H]cytochalasin B binding. The close correlation between transport activities of whole CEF and plasma membrane fractions indicates that hexose transport regulation during starvation results primarily in an increase in the number of functioning hexose transporters. The effect of protein synthesis inhibition on the overall process was studied with emetine, an inhibitor of translational elongation. Glucose-fed CEF treated with low concentrations of emetine (0.1 microM) showed a loss of transport greater than 65% within 4 h, but with higher concentrations of emetine (10 microM) there was no significant effect. Emetine treatment (0.1-10 microM) of CEF undergoing starvation virtually blocked any enhancement in transport whereas treatment of starved CEF led to only a slight loss of transport. Starved CEF refed with glucose had a decline of transport that was potentiated by low concentrations of emetine (0.1 microM); however, under these conditions high concentrations of emetine (10 microM) largely prevented loss of transport. Thus hexose transport regulation of CEF seems to reflect a balance between transporter synthesis and turnover. Transporter synthesis appears more sensitive to inhibition by emetine than turnover, whereas with hexose starvation there appears to be a decline in the activity of the transporter turnover process.