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Biomedical subjects

J M Gardner

Publications and source records attributed to J M Gardner.

At least 73 records · Page 4Linked to original sources
PubMed1983

Fibronectin expression during myogenesis.

The biosynthesis and localization of fibronectin during chick muscle differentiation are described. This study employed two monoclonal antibodies, one that selectively killed mononucleated cells and one specific for avian fibronectin. These antibodies allowed precise analyses of fibronectin expression in well-defined cultures of myoblasts or myotubes and avoided the complications of exogenous fibronectin and contamination by fibroblasts or unfused myoblasts. Fibronectin synthesis, as a fraction of total protein synthesis, remains constant at 0.3-0.4% before and after myoblast fusion, suggesting that the absolute rate of fibronectin synthesis may increase somewhat when myotubes synthesize and accumulate myofibrillar proteins. The pattern of fibronectin arrangement does change during myogenesis. In myotube cultures, the appearance of pulse-labeled fibronectin at the cell surface and its secretion into the medium begin after a 2-3-h lag period, in contrast to the 30-min lag period observed in fibroblast cultures. This lag between polypeptide biosynthesis and the exteriorization of the new protein is thus a characteristic of each cell type rather than the protein. All of the major secretory proteins of myogenic cells, including fibronectin and collagenous components, share this 2-3-h intracellular transit time.

Animals↗
PubMed1982

Identity and behavior of xylem-residing bacteria in rough lemon roots of Florida citrus trees.

An aseptic vacuum extraction technique was used to obtain xylem fluid from the roots of rough lemon (Citrus jambhiri Lush.) rootstock of Florida citrus trees. Bacteria were consistently isolated from vascular fluid of both healthy and young tree decline-affected trees. Thirteen genera of bacteria were found, the most frequently occurring genera being Pseudomonas (40%), Enterobacter (18%), Bacillus, Corynebacterium, and other gram-positive bacteria (16%), and Serratia (6%). Xylem bacterial counts fluctuated seasonally. Bacterial populations ranged from 0.1 to 22 per mm of root tissue (about 10 to 2 x 10 bacteria per g of xylem) when bacterial counts were made on vascular fluid, but these numbers were 10- to 1,000-fold greater when aseptically homogenized xylem tissue was examined similarly. Some of the resident bacteria (4%) are potentially phytopathogenic. It is proposed that xylem bacteria have an important role in the physiology of citrus.

Journal Article↗
PubMed1981

Preferential looking at temporal frequencies by preterm infants.

Preferential looking to stimuli varying in temporal frequency was examined in 11 prematurely born infants (X postconceptional age at testing = 37.6 weeks). The relationship between amount of looking and stimulus frequency yielded a significant linear trend, with the fastest frequency used (4 hertz) being most preferred. The results were interpreted as indicating that the mechanisms underlying temporal preferences differ from those underlying spatial preferences.

Arousal↗
PubMed1979

Acetylcholine receptor degradation measured by density labeling: effects of cholinergic ligands and evidence against recycling.

The methodology of density labeling of proteins by biosynthetic incorporation of 2H, 13C, 15N-amino acids into newly synthesized polypeptide chains allows the direct measurement of the turnover rate of the acetylcholine receptor in cultured chick skeletal muscle. In this study, receptors synthesized in medium containing 2H, 13C, 15N-amino acids were resolved from 1H, 12C, 14N-receptors by velocity sedimentation in sucrose-deuterium oxide gradients, and their proportions were determined by computer analysis of the gradient profiles. The kinetics of turnover of acetylcholine receptors are identical for developing chick muscle fibers grown in medium containing 2H, 13C, 15N-amino acids or 1H, 12C, 14N-amino acids, and the high degree of substitution of normal aminoacyl residues by 2H, 13C, 15N-residues does not affect the turnover rate of the denser receptor. Comparison of the turnover rates in continuous and pulse-labeling experiments gave independent confirmation of these results. The application of a potent, essentially irreversible blocking agent, alpha-bungarotoxin, increases the median lifetime of receptors from 17 hr for the native unbound receptor to 22 hr for the alpha-bungarotoxin-receptor complex. As predicted, the total number of alpha-bungarotoxin binding sites increased in the continued presence of alpha-bungarotoxin due to extension of receptor lifetime. To determine whether other cholinergic agents affect the turnover rate of the receptor, measurements were performed on cultures grown in the presence of 10(-4) M d-tubocurare or 10(-4) M carbachol, a reversible antagonist and a reversible agonist, respectively, of the nicotinic acetylcholine receptor. The receptor degradation rates of the drug-treated cells were identical to control values. The total number of alpha-bungarotoxin binding sites was reduced by 30% in the presence of carbachol, indicating that this agent affects the rate of synthesis of the acetylcholine receptor. Data formerly interpreted as suggesting a cycling of receptor-containing plasma membrane out of and back into the sarcolemma are now understood to reflect the alteration in receptor lifetime upon complexing with alpha-bungarotoxin. The intracellular "hidden" receptor sites were found to remain inside the myotubes and thus do not signify an intracellular pool of recycling plasma membrane.

Animals↗
PubMed1979

Reappearance of H1N1 influenza virus in man: evidence for the persistence of the virus in domestic chickens.

Serological studies on domestic poultry originating from China and Hong Kong suggest that the H1N1 virus may have persisted in domestic chickens prior to its reappearance in man in 1977. Experimental infection of young, local strains of poultry provided equivocal evidence that 4-day-old chickens could be infected; virus was not recovered from infected 1-month-old chickens.

Age Factors↗
PubMed1978

Sterol content of foods of plant origin.

Available data on phytosterols from the world's literature have been compiled and summarized. There still exists a paucity of data on the quantities of plant sterols in many foods. More extensive data are available on the relative sterol composition. Our compilation shows that plant oils are excellent sources of phytosterols. Nuts and seeds contain moderate levels, and fruits and vegetables generally contain the lowest concentrations of plant sterols. Analyses of the minor sterols, namely, the delta5- and delta7-phytosterols, have become available only recently.

Cholesterol↗
PubMed1977

A comparison of the community psychology and medical models: teaching attitudes toward deviance to high school students.

There is increased recognition of the importance of early intervention as part of a comprehensive system of community psychology. Moreover, emphasis on intervention at the system level is recommended to maximize effectiveness. However, in designing early intervention system-related programs, the content of the intervention is a critical, though often ignored, feature. This study compared a traditional medical model content with a community psychology-oriented content in teaching attitudes toward deviance to high school students. Results indicated that the significant changes in attitudes differed markedly between groups exposed to the divergent explanatory models, and that, in general, the community psychology model produced more favorable outcomes.

Adolescent↗
PubMed1977

Kinetics of biosynthesis of acetylcholine receptor and subsequent incorporation into plasma membrane of cultured chick skeletal muscle.

20% of the acetylcholine receptors in cultured chick skeletal muscle remain unbound following long-term growth of muscle in medium containing a potent, essentially irreversible receptor-blocking agent, alpha-bungarotoxin. About half the receptors which are unavailable for interaction with extracellular alpha-bungarotoxin are newly synthesized molecules which presumably are being processed and transported to the plasma membrane. When the muscle cultures are switched to a medium containing 2H, 13C, 15N-amino acids, these receptors are rapidly labeled, the fraction of labeled molecules beginning to plateau at 3 hr. Few labeled receptors appear in the plasma membrane during the first 3 hr of labeling with 2H, 13C, 15N-amino acids. After 3.5 hr of labeling, virtually all the receptors being incorporated into the plasma membrane are labeled receptors. The kinetics of labeling of the "pool" and "surface" receptors with 2H, 13C, 15N-amino acids confirm the "precursor-product" type relationship of pool and surface acetylcholine receptors. In this study, receptors synthesized in medium containing 2H, 13C, 15N-amino acids were resolved from 1H, 12C, 14N-receptors by velocity sedimentation in sucrose-deuterium oxide and sucrose-H2O gradients, and their densities were estimated from sedimentation rates in shallow gradients of various average density. Estimated densities were 1.32 g/cm3 for 1H, 12C, 14N-receptors and 1.41 g/cm3 for 2H, 13C, 15N-receptors. This density difference corresponds to 80% substitution of normal aminoacyl residues by 2H, 13C, 15N-residues in the denser receptor.

Acetylcholine↗
PubMed1976

High molecular weight deoxyribonucleic acid polymerase from crown gall tumor cells of periwinkle (Vinca rosea).

A high molecular weight (6 S) plant DNA polymerase from axenic Vinca rosea tissue culture cells has been purified 2200-fold and characterized. The enzyme has a molecular weight of 105 000 (+/-5000). Sodium dodecyl sulfate-acrylamide gel electrophoresis of the purified enzyme yields polypeptide subunits having molecular weights of 70 000 and 34 000. The purified enzyme has a pH optimum of 7.5; a cation requirement optimum of 6 mM Mg2+ or 0.5 mM Mn2+; an apparent requirement for Zn2+; a Km of 1 muM for dTTP; and a 3.5-fold stimulation by 50 mM KCl. The enzyme is sensitive to N-ethylmaleimide (1 mM), heparin (0.1 muM), ethanol (5%), pyrophosphate (0.05 muM), and o-phenanthroline (0.1 mM) but is insensitive to rifamycin. Denatured DNA is found to be the best natural template, and only negligible activity can be demonstrated with the ribopolymer templates poly(dT)n-poly(rA)n and p(dT)10-poly(rA)n. In addition to the polymerization reaction, the enzyme catalyzes a pyrophosphate exchange reaction. Antibody to calf thymus 6-8S DNA polymerase does not inhibit DNA polymerase from Vinca rosea, suggesting no antigenic relationships between the mammalian and plant enzymes.

Binding, Competitive↗
PubMed1976

Polygalacturonic acid trans-eliminase in the osmotic shock fluid of Erwinia rubrifaciens: characterization of the purified enzyme and its effect on plant cells.

An endopolygalacturonic acid trans-eliminase (EC 4.2.2.2), released by osmotic shock of Erwinia rubrifaciens cells, has been purified to near homogeneity (3, 100-fold) by column chromatography on diethylaminoethyl-cellulose, phosphocellulose, and hydroxyapatite-cellulose followed by isoelectric focusing. It has a molecular weight of 41,000, s20,w of 3.09S, an isoelectric point of pH 6.25, pH optimum of 9.5, and a temperature optimum of 37 C and requires Ca2+ with an optimum concentration of 0.5 to 1.0 mM. Mg2+ could not substitute for Ca2+. Tyrosinyl residues seem essential for enzyme catalysis based on rapid inactivation by tetranitromethane. The enzyme prefers unmethylated polygalacturonic acid as the substrate, cleaving alpha-1,4-glycosidic linkages randomly to form unsaturated galacturonides at a Vmax of 1,166 mumol of product/min per mg of protein and a Km of 5 mg of polygalacturonic acid per ml. Over 90% of the enzyme activity is released from osmotically shocked E. rubrifaciens cells. Unlike E. rubrifaciens, trans-eliminase is not released from Erwinia carotovora cells by osmotic shock treatment, but enzyme activity is detected in the culture medium. The release of the enzyme is reduced fivefold by the addition of dibutyryl cyclic adenosine 5'-monophosphate. The hypersensitive reaction in tobacco leaves was induced within 60 min after injection of less than 1 mug of purified E. rubrifaciens trans-eliminase. Single cells of tobacco in suspension culture are readily killed by the enzyme, whereas tobacco protoplasts remain unaffected when treated in the same manner. These results indicate that endopolygalacturonic acid trans-eliminase is a constitutive enzyme possibly located in the periplasmic space of the E. rubrifaciens cell and releases enzyme into the culture medium in the presence of substrate. The release of the enzyme in tobacco tissue and the trans-eliminative cleavage of plant cell wall components may be steps leading to hypersensitivity of the tobacco tissue.

Calcium↗
PubMed1974

Effects of host-specific toxins on electropotentials of plant cells.

Host-specific toxins from Helminthosporium victoriae (HV) and Periconia circinata (PC) caused gradual decreases in the negative electropotentials of single cells of susceptible but not of resistant plants. When tissues were held in a standard nutrient solution, the decrease (depolarization) induced by HV toxin was approximately 50 mv/hr; the decrease induced by PC toxin was even more gradual. Changes in ion efflux were detected before changes in electropotential. In contrast, toxin from H. carbonum caused a rapid but transient increase in negative electropotential of cells. Carbonyl cyanide m-chlorophenylhydrazone, which (like other metabolic inhibitors) blocks electrogenic pumps, caused cell electropotentials to decrease by approximately 50 mv within a few minutes. This suggests that HV and PC toxins do not have direct effects on electrogenic pumps, but do affect passive efflux of ions, or electrically neutral ion exchange systems, across the plasma membrane.

Journal Article↗