The Application of Electromagnetic Theory to Electrocardiology: II. Numerical Solution of the Integral Equations

In an earlier paper exact integral equations were derived for the surface potentials resulting from sources within an irregularly shaped inhomogeneous body. These exact equations cannot usually be solved. In this paper a discrete analogue is constructed which is not straightforward to solve, but which can be treated by careful mathematical methods. In particular a deflation procedure greatly facilitates the iterative solution of the problem and overcomes the divergence encountered by other authors. Numerical solutions obtained for simple geometries are compared to the exact analytic solutions available in such cases. The necessary convergence of the solutions of the discrete analog towards the solution of the continuous problem is shown to occur only if the coefficients of the discrete analogue are carefully evaluated. Calculations are then presented for realistic thoracic geometries, typical results being presented as surface potential maps. Finally the important effect of the internal regional inhomogeneities, particularly a realistic cardiac blood mass, is demonstrated by obtaining vector loops with and without these effects.     

The path integral for dendritic trees

We construct the path integral for determining the potential on any dendritic tree described by a linear cable equation. This is done by generalizing Brownian motion from a line to a tree. We also construct the path integral for dendritic structures with spatially-varying and/or time-dependent membrane conductivities due, for example, to synaptic inputs. The path integral allows novel computational techniques to be applied to cable problems. Our anlaysis leads ultimately to an exact expression for the Green's function on a dendritic tree of arbitrary geometry expressed in terms of a set of simple diagrammatic rules. These rules providing a fast and efficient method for solving complex cable problems.Research supported by Department of Energy Contracts DE-AC02-76ER03230 and DE-AC02-76ER03069 and by National Institute of Mental Health grant MH46742     

Racism and liberalism: the dynamics of inclusion and exclusion

This essay explores the argument that David Scott FitzGerald and David Cook-Martín make in their book Culling the Masses about the relationship between liberalism and racism, in terms of a balance between inclusion and exclusion. I challenge their dismissal of approaches that see an integral connection between the two and of approaches that see liberalism as inherently opposed to racism. I also discuss their characterization of Latin American ‘racist anti-racism’ and finish by questioning the way that they separate racism from economics.     

Approximate standard errors in semiparametric models

We consider semiparametric models with p regressor terms and q smooth terms. We obtain an explicit expression for the estimate of the regression coefficients given by the back-fitting algorithm. The calculation of the standard errors of these estimates based on this expression is a considerable computational exercise. We present an alternative, approximate method of calculation that is less demanding. With smoothing splines, the method is exact, while with loess, it gives good estimates of standard errors. We assess the adequacy of our approximation and of another approximation with the help of two examples.     

Investigation of the Application of miR10b and miR135b in the Identification of Semen Stains

To evaluate the identification method using the microRNA markers miR10b and miR135b to distinguish semen stains from menstrual blood, peripheral blood, vaginal fluid and so on body fluid stains. The expression levels of miR10b and miR35b in semen stains and menstrual blood and so on were detected utilizing a real-time quantitative PCR technique with a specific fluorescence-labeled TaqMan probe. RNU6b was used as the internal reference gene; the difference in their expression was analyzed, and the specificity, sensitivity, and detection capability of the techniques were evaluated. The expression of miR10b and miR135b in semen stains was significantly higher than that of other body fluid stains, with a mean value of ΔCт from-6 to-7. However, it ranged from-2 to-4 for other body fluid stains. The initial criteria for judging which semen stains can be identified were determined by analyzing the research results. When the threshold value was set to 0.04, the C_T value could be detected in the target genes miR10b, miR135b and in the internal reference gene RNU6b, and C_T values are<40, ΔC_T[10b-U6]<-5.5, and ΔC_T[135b-U6]<-6, respectively, and the semen stain could be identified. The expression levels of miR10b and miR135b are higher in semen with strong tissue specificity; thus, they can be used to differentiate semen stains from other body fluid stains in forensic science.     

Preparation and epitope characterization of monoclonal antibodies against firefly luciferase

The 6-His tagged firefly luciferase was highly expressed inE. coli and purified to homogeneity by affinity chromatography and gel filtration. After immunizing Balb/c mice with the antigen, 6 hybridomas clones were found to secrete monoclonal antibodies (mAbs) and the mAbs were also purified separately. The competitive binding experiments show that 2 mAbs can bind heat-denatured antigen or its proteolytic fragments but not the native luciferase, suggesting that their epitopes might be accommodated in the internal segments of the protein. On the other hand, the other 4 mAbs are capable of binding both native and denatured antigens. It infers that their epitopes locate in the segments on the protein surface. The results also suggest that the six mAbs are all sequence-specific.     

Configuration of the medial and lateral segments of duck (Anas platyrhynchos) salt glands

Salt glands of the domestic duck Anas platyrhynchos differ from those of the herring gull Larus argentatus and other birds. In ducks, each salt gland consists of distinct medial and lateral segments. Centrally located drainage ducts that extend along the entire length of these medial and lateral segments collect hypertonic fluid secreted by an array of lobules. Each lobule is formed by a single mass of branched tubules in which the direction of capillary blood flow is opposite to that of the secreted fluid. This fluid drains from the medial segment through an external duct that opens into the nasal cavity at the base of the vestibular fold. A duct from the lateral segment loops and opens onto the surface of the nasal septum. The structure and function of the secretory cells is reviewed briefly within the context of our study of the configuration of duck nasal salt glands.     

Hydrocarbon distribution and colony odour homogenisation in <Emphasis Type="Italic">Pachycondyla apicalis</Emphasis>

Summary Within and between individuals hydrocarbon (HC)-circulation was studied in Pachycondyla apicalis workers, using radioactive labeling. Newly synthesized HCs occurred both in the PPG and on the epicuticle in appreciable amounts, lesser quantities were found in the crop. The front basitarsal brush contained a greater amount of radiolabeled HCs than could be predicted from its surface area, suggesting preferential secretion to these organs. We propose that the newly synthesized HCs are secreted primarily to the front basitarsal brushes and are thereafter either distributed throughout the body surface, or cleared via the PPG and the alimentary canal.Using labeled HCs as a model, we tracked the time-dependent dispersion of cuticular lipids among 11 workers, one of which was prelabeled for 24 hours. Distribution among the recipients became progressively uniform, reaching near homogenization between 5–10 days. The mean HCs transfer of P. apicalis to the PPG was substantially lower compared to that of Camponotus fellah or Aphaenogaster senilis. In contrast, transfer to the cuticle in this species was superior. We attribute the low transfer to the PPG to the inefficacy of passive body contact characteristic of P. apicalis, as opposed to trophallaxis and/or allogrooming that typify the other two species. The higher occurrence of radiolabeled HCs in P. apicalis cuticle can be attributed to their accumulation in the basitarsal brushes. The impact of cuticular lipid transfer and formation of uniform colony odour, as opposed to the maintenance of an idiosyncratic caste-specific composition, are discussed.Received 5 September 2002; revised 17 January 2003; accepted 10 February 2003.     

Evolution of the MIP family of integral membrane transport proteins

Six integral membrane proteins of bacterial, animal, and plant origin, which are believed to function in solute transport, share sequence identity and are grouped together as members of the MIP family. These include the Escherichia coli glycerol facilitator, the major intrinsic protein from bovine lens fibre junction membranes, a plant tonoplast membrane protein, a soybean protein from the peribacteroid membrane, and a Drosophila neurogenic protein. These proteins, each of which appears to consist of six transmembrane helical segments per subunit, apparently arose by internal duplication of a three-transmembrane segment. Phylogenetic‘trees’interrelating these proteins and segments are presented.     

The fine structure of the tegument of Tylocephalum metacestodes: With emphasis on a new type of microvilli

Electron microscope studies on Tylocephalum metacestodes embedded in the tissues of the oyster, Crassostrea virginica, have revealed that the tegument of the larval tapeworm is comprised of an external and an internal level which are partially separated by a basal lamina and two layers of muscles. The outer tegumentary level is comprised of an anucleate, cytoplasmic syncytium in which are embedded large and small vesicles and mitochondria. Surfacial hooks are also embedded therein. The internal level is comprised of relatively large discrete cells including mitochondria, rough endoplasmic reticulum, and large and small vesicles. These cells are intermittently connected with the external level by cytoplasmic bridges. Arising from the external level are unusual microvilli each of which terminates as a spherical vesicle. The stem of each microvillus is covered by a unit membrane which is continuous with that overlaying the body surface. In addition, each microvillus includes an external layer of medium electron density, a medial layer of intense electron density, and a core of heterogenous, medium electron density. These structures may be intertwined and bundles can be observed at the light microscope level as fibril-like projections from the parasite's body surface. One of their possible functions may be to prevent intimate contact between the encapsulating fibers of host origin and the parasite's body surface. In addition, the contraction and distention of the circular muscles result in microvillar movement which may keep the surrounding host fluids, including those of nutritional importance to the parasite, in a state of flux thus hypothetically permitting more uniform uptake. The abundance of vesicles in the syncytial external level of the tegument appears to be characteristic of the more primitive marine cestodes belonging to the orders Trypanorhyncha and Lecanicephala.     

Scanning electron microscopic analysis of spontaneous and UV-induced abnormal segment patterns in Chironomus samoensis (Diptera,Chironomidae)

Summary The embryonic body pattern of Chironomus samoensis, as well as other chironomids, can be altered dramatically by irradiating their eggs with ultraviolet light (UV). Anterior UV irradiation leads to the formation of double abdomen embryos whose anterior segments are replaced by posterior segments with reversed polarity. Most double abdomens are symmetrical showing a mirror image duplication of the posterior six or seven segments. However, in some cases the anterior end of the double abdomen is shorter, and comprises fewer segments, than its posterior counterpart. These asymmetries range from moderate to extreme. They involve the juxtaposition, at the plane of polarity reversal, of disparate segments. The same range of symmetrical and asymmetrical double abdomens is also formed spontaneously in an apparently mutant strain of C. samoensis. There are striking similarities between this natural variant and the Drosophila melanogaster mutant bicaudal which are also discussed with respect to models of embryonic pattern formation.     

Introductory Lecture: In Vitro Translation Analysis of Integral Membrane Proteins

Abstract

A method of in vitro translation scanning was applied to a variety of polytopic integral membrane proteins, a transition metal P type ATPase from Helicobacter pylori, the SERCA 2 ATPase, the gastric H⁺,K⁺ ATPase, the CCK-A receptor and the human ileal bile acid transporter. This method used vectors containing the N terminal region of the gastric H⁺,K⁺ ATPase or the N terminal region of the CCK-A receptor, coupled via a linker region to the last 177 amino acids of the β-subunit of the gastric H⁺,K⁺ ATPase. The latter contains 5 potential N-linked glycosylation sites. Translation of vectors containing the cDNA encoding one, two or more putative transmembrane domains in the absence or presence of microsomes allowed determination of signal anchor or stop transfer properties of the putative transmembrane domains by the molecular weight shift on SDS PAGE. The P type ATPase from Helicobacter pylori showed the presence of 8 transmembrane segments with this method. The SERCA 2 Ca²⁺ ATPase with this method had 9 transmembrane co-translational insertion domains and coupled with other evidence these data resulted in a 11 transmembrane segment model. Translation of segments of the gastric H⁺,K⁺ ATPase provided evidence for only 7 transmembrane segments but coupled with other data established a 10 membrane segment model. The G7 protein, the CCK-A receptor showed the presence of 6 of the 7 transmembrane segments postulated for this protein. Translation of segments of the human ileal bile acid transporter showed the presence of 8 membrane insertion domains. However, translation of the intact protein provided evidence for an odd number of transmembrane segments, resulting in a tentative model containing 7 or 9 transmembrane segments. Neither G7 type protein appeared to have an arrangement of sequential topogenic signals consistent with the final assembled protein. This method provides a useful addition to methods of determining membrane domains of integral membrane proteins but must in general be utilized with other methods to establish the number of transmembrane α-helices.     

Hydrodynamics of bolus flow—An analytical approach to blood flow in capillaries

A model which was used by Prothero and Burton to simulate a particular configuration in capillary blood vessels is investigated from a hydrodynamic point of view. In this model, the erythrocytes are approximated by rigid pistons, and plasma is assumed to be an incompressible Newtonian fluid. An order of magnitude analysis using the physiologically realistic values for various parameters reduces the exact equations of motion to an equation describing the creeping motion of the fluid. An analytical approach to the solution of the equation is proposed and some results are reported here. The solution of the flow field is given in terms of a stream function which is represented by two infinite series composed of known functions. Two coupled infinite systems of algebraic equations determining the coefficients of the two series have been derived. This method of solution is proposed as an alternative to the entirely numerical procedure of solving the similar problem proposed by Bugliarelloet al. A limiting case of large aspect ratio (the ratio of the axial spacing of the two successive erythrocytes to the capillary diameter) is studied and the solution, valid away from the erythrocyte surface, has been obtained in simple form. It resembles the classical Poisenille flow, but the pressure gradient is related to the erythrocyte speed.     

Localization of the chemoreceptive properties of the surface membrane ofParamecium tetraurelia

Summary The plasma membrane ofParamecium tetraurelia comprises two morphologically distinct components; a membrane that encloses the cell body and a ciliary membrane. In order to investigate the relative contributions of the two membranes to attractant-induced membrane potential changes, cells were deciliated with ethanol and their subsequent responses to attractants examined.Deciliation did not significantly affect the magnitude of the hyperpolarizations evoked by acetic or lactic acids, and had no effect on the concentration dependence of responses to folic acid. We conclude that the components necessary for detection and response to attractants are not exclusive to the ciliary membrane ofP. tetraurelia. Deciliation ofParamecium concomitantly permits localized chemical stimuli to be applied directly to the cell surface in the absence of strong fluid currents that are generated by the activity of the locomotory organelles. By systematically applying K₂ folate to a number of sites on the cell surface, it has been possible to demonstrate an anterior-posterior gradient of chemosensitivity on the cell body ofP. tetraurelia.     

Internal structure of the postcapillary high-endothelial venules of rodent lymph nodes and Peyer's patches and the transendothelial lymphocyte passage

Scanning electron microscopy (SEM) shows that the postcapillary high-endothelial venules of lymph nodes and Peyer's patches consist of two segments each with a different surface relief: a proximal segment with a cobblestone surface pattern and a distal segment of interlacing cytoplasmic plates. Both segments have deep adluminal crevices in which lymphocytes are lodged. The internal structural configuration of this endothelium has been examined by transmission electron microscopy (TEM) of serial sections of lymph nodes and Peyer's patches of mice, rats, and guinea pigs. The serial sections revealed that the endothelial cell bodies and their cytoplasmic extensions were disposed in a direction generally lateral to the luminal surface and intruded into the intercellular spaces of similarly disposed neighboring endothelial cells, resulting in a complex interlacing cellular pattern. Lymphocytes penetrated the endothelial cell body and secondarily followed an intracellular pathway through which they entered the extravascular compartment. At the exposed surfaces of the adluminal venule wall, recirculating lymphocytes were seen in SEM images to enter the endothelium by penetrating the endothelial cell body. The mode of migration of lymphocytes lodged in the endothelial crevices could be determined by SEM and has been examined by TEM of serial sections. At these locations as at the exposed surfaces, lymphocytes also entered the venule by penetrating the endothelial cell body. At both sites this transcellular pathway was followed by lymphocyte entry into the intercellular spaces from which they migrated into the extravascular compartment.     

Topology of the PhoR protein of Escherichia coli and functional analysis of internal deletion mutants

The PhoR protein of Escherichia coli K-12 belongs to a family of structurally related sensor-kinases that regulate responses to environmental stimuli. These proteins are often located in the inner membrane with two membrane-spanning segments that are separated by a periplasmic domain, which is supposed to sense the environmental stimuli. However, the hydrophobicity plot of PhoR suggests a somewhat different topology in which a large periplasmic domain is lacking and an extended cytoplasmic domain is present besides the kinase domain. In protease-accessibility experiments and by using phoR-phoA gene fusions, the topology of PhoR was investigated and the absence of a large periplasmic domain was confirmed. Furthermore, the function of the extended cytoptasmic domain was studied by creating internal deletions. The mutations in this domain resulted in a constitutive expression of the pho regulon, indicating that the mutant PhoR proteins are locked in their kinase function. We propose that this extended cytoplasmic domain functions by sensing an internal signal that represses the kinase function of the PhoR protein.     

Backbone entropy of loops as a measure of their flexibility: Application to a Ras protein simulated by molecular dynamics

The flexibility of surface loops plays an important role in protein–protein and protein–peptide recognition; it is commonly studied by Molecular Dynamics or Monte Carlo simulations. We propose to measure the relative backbone flexibility of loops by the difference in their backbone conformational entropies, which are calculated here with the local states (LS) method of Meirovitch. Thus, one can compare the entropies of loops of the same protein or, under certain simulation conditions, of different proteins. These loops should be equal in size but can differ in their sequence of amino acids residues. This methodology is applied successfully to three segments of 10 residues of a Ras protein simulated by the stochastic boundary molecular dynamics procedure. For the first time estimates of backbone entropy differences are obtained, and their correlation with B factors is pointed out; for example, the segments which consist of residues 60–65 and 112–117 have average B factors of 67 and 18 Ų, respectively, and entropy difference T ΔS = 5.4 ± 0.1 kcal/mol at T = 300 K. In a large number of recent publications the entropy due to the fast motions (on the ps-ns time scale) of N–H and C–H vectors has been obtained from their order parameter, measured in nuclear magnetic resonance spin relaxation experiments. This enables one to estimate differences in the entropy of protein segments due to folding–unfolding transitions, for example. However, the vectors are assumed to be independent, and the effect of the neglected correlations is unknown; our method is expected to become an important tool for assessing this approximation. The present calculations, obtained with the LS method, suggest that the errors involved in experimental entropy differences might not be large; however, this should be verified in each case. Potential applications of entropy calculations to rational drug design are discussed. Proteins 29:127–140, 1997. © 1997 Wiley-Liss, Inc.