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M Yeager

Publications and source records attributed to M Yeager.

68 records · Page 4Linked to original sources
PubMed1992

Membrane topology and quaternary structure of cardiac gap junction ion channels.

The membrane topology and quaternary structure of rat cardiac gap junction ion channels containing alpha 1 connexin (i.e. Cx43) have been examined using anti-peptide antibodies directed to seven different sites in the protein sequence, cleavage by an endogenous protease in heart tissue and electron microscopic image analysis of native and protease-cleaved two-dimensional membrane crystals of isolated cardiac gap junctions. Specificity of the peptide antibodies was established using dot immunoblotting, Western immunoblotting, immunofluorescence and immunoelectron microscopy. Based on the folding predicted by hydropathy analysis, five antibodies were directed to sites in cytoplasmic domains and two antibodies were directed to the two extracellular loop domains. Isolated gap junctions could not be labeled by the two extracellular loop antibodies using thin-section immunogold electron microscopy. This is consistent with the known narrowness of the extracellular gap region that presumably precludes penetration of antibody probes. However, cryo-sectioning rendered the extracellular domains accessible for immunolabeling. A cytoplasmic "loop" domain of at least Mr = 5100 (residues (101 to 142) is readily accessible to peptide antibody labeling. The native Mr = 43,000 protein can be protease-cleaved on the cytoplasmic side of the membrane, resulting in an Mr approximately 30,000 membrane-bound fragment. Western immunoblots showed that protease cleavage occurs at the carboxy tail of the protein, and the cleavage site resides between amino acid residues 252-271. Immunoelectron microscopy demonstrated that the Mr approximately 13,000 carboxy-terminal peptide(s) is released after protease cleavage and does not remain attached to the Mr approximately 30,000 membrane-bound fragment via non-covalent interactions. Electron microscopic image analysis of two-dimensional membrane crystals of cardiac gap junctions revealed that the ion channels are formed by a hexagonal arrangement of protein subunits. This quaternary arrangement is not detectably altered by protease cleavage of the alpha 1 polypeptide. Therefore, the Mr approximately 13,000 carboxyterminal domain is not involved in forming the transmembrane ion channel. The similar hexameric architecture of cardiac and liver gap junction connexins indicates conservation in the molecular design of the gap junction channels formed by alpha or beta connexins.

Amino Acid Sequence↗
PubMed1990

Three-dimensional structure of rhesus rotavirus by cryoelectron microscopy and image reconstruction.

The structure of rhesus rotavirus was examined by cryoelectron microscopy and image analysis. Three-dimensional reconstructions of infectious virions were computed at 26- and 37-A resolution from electron micrographs recorded at two different levels of defocus. The major features revealed by the reconstructions are (a) both outer and inner capsids are constructed with T = 13l icosahedral lattice symmetry; (b) 60 spikelike projections, attributed to VP4, extend at least 100 A from the outer capsid surface; (c) the outer capsid, attributed primarily to VP7, has a smoothly rippled surface at a mean radius of 377 A and is perforated by 132 aqueous holes ranging from 40-65 A in diameter; (d) the inner capsid has a "bristled" outer surface composed of 260 trimeric-shaped columns of density, attributed to VP6, which merge with a smooth, spherical shell of density at a lower, mean radius of 299 A, and which is perforated by holes in register with those in the outer capsid; (e) a "core" region contains a third, nonspherical shell of density at a mean radius of 225 A that encapsidates the double-stranded RNA genome; and (f) the space between the outer and inner capsids forms an open aqueous network that may provide pathways for the diffusion of ions and small regulatory molecules as well as the extrusion of RNA. The assignment of different viral structural proteins to specific features of the reconstruction has been tentatively made on the basis of excluded volume estimates and previous biochemical characterizations of rotavirus.

Animals↗
PubMed1986

Comparison of Doppler-derived pressure gradient to that determined at cardiac catheterization in adults with aortic valve stenosis: implications for management.

Over a 1-year period cardiac catheterization was performed in 58 patients, mean age 66 years, who had elevated aortic blood flow velocity (more than 1.7 m/s) by continuous-wave Doppler echocardiography. Doppler echo signals were initially judged acceptable for quantitative analysis in 95% of patients, usually from the apical transducer position. Cardiac catheterization was performed within a mean of 8 days (60% within 1 day) of the Doppler echo study. The aortic valve mean pressure gradients at catheterization ranged from 0 to 93 mm Hg. The linear correlation coefficient (r value) between the mean pressure gradient determined by Doppler echocardiography and catheterization was 0.87. The correlation was maintained in 15 patients with aortic regurgitation (r = 0.91) and in 16 patients with significant coronary artery disease (r = 0.93). In the 16 patients with reduced cardiac output (mean 3.2 liters/min, range 2.2 to 3.9) the correlation was 0.81. A strategy for using the Doppler echo-calculated pressure gradient to manage patients with valvular aortic stenosis (AS) was derived by investigating the relation of the Doppler echo gradient to the aortic valve area in 35 patients with no aortic regurgitation detected at catheterization. All 12 patients with a Doppler echo mean gradient of less than 30 mm Hg had an aortic valve area of more than 0.75 cm2 and all 11 patients with a Doppler echo mean gradient of more than 50 mm Hg had an aortic valve area of less than 0.75 cm2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Doppler echocardiographic measurement of aortic valve area in aortic stenosis: a noninvasive application of the Gorlin formula.

Thirty adult patients with aortic stenosis had Doppler echocardiography within 1 day of cardiac catheterization. Noninvasive measurement of the mean transaortic pressure gradient was calculated by applying the simplified Bernoulli equation to the continuous wave Doppler transaortic velocity recording. Stroke volume was measured noninvasively by multiplying the systolic velocity integral of flow in the left ventricular outflow tract (obtained by pulsed Doppler ultrasonography) by the cross-sectional area of the left ventricular outflow tract (measured by two-dimensional echocardiography). Non-invasive measurement of aortic valve area was calculated by two methods. In method 1, the Gorlin equation was applied using Doppler-derived mean pressure gradient, cardiac output and systolic ejection period. Method 2 used the continuity equation. These noninvasive measurements were compared with invasive measurements using linear regression analysis, and mean pressure gradients correlated well (r = 0.92). Aortic valve area by either noninvasive method also correlated well with cardiac catheterization values (method 1, r = 0.87; method 2, r = 0.88). The sensitivity of Doppler detection of critical aortic stenosis was 0.86, with a specificity of 0.88 and a positive predictive value of 0.86. Cardiac output measured nonsimultaneously showed poor correlation (r = 0.51). Doppler echocardiography can distinguish critical from noncritical aortic stenosis with a high degree of accuracy. Measurement of aortic valve area aids interpretation of Doppler-derived mean pressure gradient data when the gradients are in an intermediate range (30 to 50 mm Hg).

Aortic Valve Stenosis↗
PubMed1984

Thrombotic and infectious complications of Hickman-Broviac catheters.

Hickman-Broviac catheters are often used when long-term venous access is required. Although generally safe, catheter-related thrombosis and infection are two of the most frequent and clinically important complications associated with their use. A 47-year-old woman with breast cancer had a Hickman catheter placed for chemotherapy; subsequently, the superior vena caval syndrome developed due to a large thrombus surrounding the catheter tip. A very low dose of streptokinase successfully lysed this clot within 12 hours. A 60-year-old woman with acute myelogenous leukemia had a Hickman catheter placed to facilitate induction and maintenance chemotherapy. Two episodes of catheter-related Staphylococcus epidermidis sepsis later developed, the first of which cleared without removal of the cannula.

Breast Neoplasms↗
PubMed1976

Lipoprotein lipase in rat lung. Effect of dexamethasone.

The effect of hormone administration on the activity of lipoprotein lipase in the lung was studied in the rat. The following hormones were administered: dexamethasone, L-thyroxine, estradiol-17beta and progesterone. In addition, lung lipoprotein lipase activity was studied in diabetic and lactating rats. Lipoprotein lipase activity was measured in dried, defatted preparations of rat lung using double labeled ([14C]palmitate, [3H]glycerol) chylomicron triacylglycerol as substrate. Dexamethasone administration caused a rise of 70% in the level of activity of lipoprotein lipase in acetone powders of lung and a 100% increase in the amount of enzyme released during heparin infusion into isolated, perfused lungs. Enzyme activity was higher in lungs of females than of male rats; however; the level of activity was unaffected by estrogen or progesterone administration to either male or ovariectomized rats. Diabetes, hyperthyroidism or lactation did not change lipoprotein lipase activity in the lung. The constant presence of lipoprotein lipase activity in the lung suggests that this organ is able to maintain a steady supply of triacylglycerol-fatty acids under a variety of physiological and pathological conditions. Stimulation of enzyme activity by dexamethasone could lead to increased uptake of triacylglycerol-fatty acids by the lung and may thus be a contributing factor to corticosteroid-induced enhanced surfactant synthesis.

Animals↗
PubMedDate not supplied

AVS software for visualization in molecular microscopy.

AVS (Application Visualization System) is commercially available software for analyzing and viewing data. AVS is primarily used in the physical sciences and engineering, and here we describe the application of AVS for examining three-dimensional density maps generated by electron microscopy and image processing. For this purpose, AVS can be applied with relative ease, even though the software is indeed quite sophisticated. The primary advantage is that visualization applications can be generated by combining software components, called modules, into executable flow networks. Simple networks are described for generating ribbon diagrams of macromolecules, surface-shaded views, and contour maps. Easy to use dials, bar sliders, and buttons provide tremendous versatility for real-time manipulation of isosurface values, depth cueing, view orientation, size, and animation. In addition, AVS supplies a framework for building new modules in C or FORTRAN. Modules for excavation and cropping provide tools that are particularly useful for extracting segments of a map and for examining maps of supramolecular complexes such as viruses. We describe a number of modules we have designed for analysis of three-dimensional data sets, as well as modules for importing image data from other software packages into AVS. We also describe xformat, a stand-alone file conversion utility designed to allow import of a variety of image and map file formats into AVS.

Capsid↗
PubMedDate not supplied

The role of the registered nurse-first assistant in the implantable left ventricular assist device program.

Successful support of patients using the implantable left ventricular assist device requires sustained and coordinated efforts by physicians and medical personnel. The authors describe the role of their registered nurse-first assistant (RNFA) as it has evolved through caring for 43 implantable pneumatic left ventricular assist device patients and 8 vented-electric left ventricular assist system patients during a 3 year period. Intraoperatively, the RNFA is responsible for pump assembly, including pre sealing all grafts and connecting areas of the pump using a combination of cryoprecipitate and thrombin. The RNFA assists with pump insertion during surgery. At device explantation, the RNFA dismantles the pump according to the FDA protocol for disassembly. Post operatively, the RNFA assesses and maintains patient hemodynamic stability and intervenes to manage hemodynamic and mechanical problems. Of the 51 patients, 13 are still on support, 9 died before transplantation (17.6%), and post transplant survival is 96.0%. In conclusion, an active left ventricular assist device program requires skilled personnel to manage complex problems and contributes to a successful patient outcome.

Heart Transplantation↗