Biomedical subjects

John Ross

Publications and source records attributed to John Ross.

At least 73 records · Page 4Linked to original sources

PubMed2002

Direct evidence that "speedlines" influence motion mechanisms.

Determining the direction of visual motion poses a serious problem for any visual system, given the inherent ambiguities. Geisler (1999) has suggested that motion streaks left in the wake of a moving target provide a rich source of potential information that could aid in resolving direction ambiguities. Here we provide strong experimental evidence that the human visual system does in fact exploit motion streaks in direction discrimination. Masks comprising oriented random noise impeded direction discrimination of moving dots when the masks were oriented parallel to the direction of motion but had very little effect when oriented orthogonal to the direction of motion. The masking effect decreased systematically with increasing bandwidth for the parallel masks and increased with bandwidth for the orthogonal masks. Importantly, these masks had little effect on neither contrast sensitivity for detecting the moving stimuli nor for speed discrimination. Experiments with "Glass patterns" (moiré patterns constructed from random dot pairs) confirmed that misleading pattern information can impede motion detection. The results show that the oriented streaks left by moving stimuli provide fundamental information about the direction of visual motion; removing these streaks or augmenting them with erroneous streaks severely confounds motion direction discrimination.

Contrast Sensitivity↗

PubMed2002

Akt induces enhanced myocardial contractility and cell size in vivo in transgenic mice.

The serine-threonine kinase Akt seems to be central in mediating stimuli from different classes of receptors. In fact, both IGF-1 and IL6-like cytokines induce hypertrophic and antiapoptotic signals in cardiomyocytes through PI3K-dependent Akt activation. More recently, it was shown that Akt is involved also in the hypertrophic and antiapoptotic effects of beta-adrenergic stimulation. Thus, to determine the effects of Akt on cardiac function in vivo, we generated a model of cardiac-specific Akt overexpression in mice. Transgenic mice were generated by using the E40K, constitutively active mutant of Akt linked to the rat alpha-myosin heavy chain promoter. The effects of cardiac-selective Akt overexpression were studied by echocardiography, cardiac catheterization, histological and biochemical techniques. We found that Akt overexpression produced cardiac hypertrophy at the molecular and histological levels, with a significant increase in cardiomyocyte cell size and concentric LV hypertrophy. Akt-transgenic mice also showed a remarkable increase in cardiac contractility compared with wild-type controls as demonstrated by the analysis of left ventricular (dP/dt(max)) in an invasive hemodynamic study, although with graded dobutamine infusion, the maximum response was not different from that in controls. Diastolic function, evaluated by left ventricular dP/dt(min), was not affected at rest but was impaired during graded dobutamine infusion. Isoproterenol-induced cAMP levels, beta-adrenergic receptor (beta-AR) density, and beta-AR affinity were not altered compared with control mice. Moreover, studies on signaling pathway activation from myocardial extracts demonstrated that glycogen synthase kinase3-beta is phosphorylated, whereas p42/44 mitogen-activated protein kinases is not, indicating that Akt induces hypertrophy in vivo by activating the glycogen synthase kinase3-beta/GATA 4 pathway. In summary, our results not only demonstrate that Akt regulates cardiomyocyte cell size in vivo, but, importantly, show that Akt modulates cardiac contractility in vivo without directly affecting beta-AR signaling capacity.

Animals↗

PubMed2002

Memory effects and oscillations in single-molecule kinetics.

An exactly solvable model for single-molecule kinetics is suggested, based on the following assumptions: (i) A single molecule can exist in different chemical states and the random transitions from one chemical state to another can be described by a local master equation with time-dependent transition rates. (ii) Because of conformational and other intramolecular fluctuations the rate coefficients in the master equation are random functions of time; their stochastic properties are represented in terms of a set of control parameters. We assume that the fluctuating rate coefficients fulfill a separability condition, that is, they are made up of the multiplicative contributions of two factors: (a) a universal factor, which depends on the vector of control parameters and is the same for all chemical transformation processes and (b) process-dependent factors, which depend on the initial and final chemical states of the molecule but are independent of the control parameters. For systems with two chemical states the condition of separability is automatically fulfilled. We introduce an intrinsic time scale, which makes it possible to compute theoretically various experimental observables, such as the correlation functions of the fluorescent signal. We analyze the connections between the condition of separability and detailed balance, and discuss the possible cause of chemical oscillations in single molecule kinetics. We show that the intrinsic dynamics of the molecule, expressed by the fluctuations of the control parameters, may lead to damped oscillations of the correlation functions of the fluorescent signal. The influence of the random fluctuations on the control parameters may be described by a renormalized master equation with nonfluctuating apparent rate coefficients. The apparent rate coefficients do not have to obey a condition of detailed balance, even though the real rate coefficients do obey such a condition. It follows that the renormalized master equation may have damped oscillatory solutions.

Kinetics↗

PubMed2002

Defects in caveolin-1 cause dilated cardiomyopathy and pulmonary hypertension in knockout mice.

Caveolins are important components of caveolae, which have been implicated in vesicular trafficking and signal transduction. To investigate the in vivo significance of Caveolins in mammals, we generated mice deficient in the caveolin-1 (cav-1) gene and have shown that, in the absence of Cav-1, no caveolae structures were observed in several nonmuscle cell types. Although cav-1(-/-) mice are viable, histological examination and echocardiography identified a spectrum of characteristics of dilated cardiomyopathy in the left ventricular chamber of the cav-1-deficient hearts, including an enlarged ventricular chamber diameter, thin posterior wall, and decreased contractility. These animals also have marked right ventricular hypertrophy, suggesting a chronic increase in pulmonary artery pressure. Direct measurement of pulmonary artery pressure and histological analysis revealed that the cav-1(-/-) mice exhibit pulmonary hypertension, which may contribute to the right ventricle hypertrophy. In addition, the loss of Cav-1 leads to a dramatic increase in systemic NO levels. Our studies provided in vivo evidence that cav-1 is essential for the control of systemic NO levels and normal cardiopulmonary function.

Animals↗

PubMed2002

Chronic suppression of heart-failure progression by a pseudophosphorylated mutant of phospholamban via in vivo cardiac rAAV gene delivery.

The feasibility of gene therapy for cardiomyopathy, heart failure and other chronic cardiac muscle diseases is so far unproven. Here, we developed an in vivo recombinant adeno-associated virus (rAAV) transcoronary delivery system that allows stable, high efficiency and relatively cardiac-selective gene expression. We used rAAV to express a pseudophosphorylated mutant of human phospholamban (PLN), a key regulator of cardiac sarcoplasmic reticulum (SR) Ca(2+) cycling in BIO14.6 cardiomyopathic hamsters. The rAAV/S16EPLN treatment enhanced myocardial SR Ca(2+) uptake and suppressed progressive impairment of left ventricular (LV) systolic function and contractility for 28-30 weeks, thereby protecting cardiac myocytes from cytopathic plasma-membrane disruption. Low LV systolic pressure and deterioration in LV relaxation were also largely prevented by rAAV/S16EPLN treatment. Thus, transcoronary gene transfer of S16EPLN via rAAV vector is a potential therapy for progressive dilated cardiomyopathy and associated heart failure.

Adenosine Triphosphatases↗

PubMed2002

Neutrality condition and response law for nonlinear reaction-diffusion equations, with application to population genetics.

We study a general class of nonlinear macroscopic evolution equations with "transport" and "reaction" terms which describe the dynamics of a species of moving individuals (atoms, molecules, quasiparticles, organisms, etc.). We consider that two types of individuals exist, "not marked" and "marked," respectively. We assume that the concentrations of both types of individuals are measurable and that they obey a neutrality condition, that is, the kinetic and transport properties of the "not marked" and "marked" individuals are identical. We suggest a response experiment, which consists in varying the fraction of "marked" individuals with the preservation of total fluxes, and show that the response of the system can be represented by a linear superposition law even though the underlying dynamics of the system is in general highly nonlinear. The linear response law is valid even for large perturbations and is not the result of a linearization procedure but rather a necessary consequence of the neutrality condition. First, we apply the response theorem to chemical kinetics, where the "marked species" is a molecule labeled with a radioactive isotope and there is no kinetic isotope effect. The susceptibility function of the response law can be related to the reaction mechanism of the process. Secondly we study the geographical distribution of the nonrecurrent, nonreversible neutral mutations of the nonrecombining portion of the Y chromosome from human populations and show that the fraction of mutants at a given point in space and time obeys a linear response law of the type introduced in this paper. The theory may be used for evaluating the geographic position and the moment in time where and when a mutation originated.

Biochemical Phenomena↗

PubMed2002

Determination of causal connectivities of species in reaction networks.

We present an approach to the determination of causal connectivities and part of the kinetics of complex reaction systems. Our approach is based on analytical and computational methods for studying the effects of a pulse change of concentration of a chemical species in a reaction network, either at equilibrium or in a nonequilibrium stationary state. Such disturbances generally propagate through a few species, depending on the values of the kinetic coefficients, before being broadened and dissipated. This short range gives a local probe of the kinetics and connectivity of the reaction network. The range of propagation also indicates species to perturb in further experiments. From piecing together these local connectivities, the global structure of the network can be constructed. The experimental design allows deduction of both reaction orders and rate constants in many cases. An example of the usefulness of the approach is illustrated on a model of a part of glycolysis.

Adenosine Triphosphate↗

PubMed2002

Restoration of deficient membrane proteins in the cardiomyopathic hamster by in vivo cardiac gene transfer.

BACKGROUND: One of the most important problems in developing in vivo cardiac gene transfer has been low transfection efficiency. A novel in vivo technique was developed, tested in normal hamsters, and the feasibility of restoring a deficient structural protein (delta-sarcoglycan) in the cardiomyopathic (CM) hamster evaluated. METHODS AND RESULTS: Adenoviral (AdV) vectors encoding either the lacZ gene or delta-sarcoglycan gene were constructed. Hypothermia was achieved in hamsters by external body cooling to a rectal temperature of 18 to 25 degrees C. Through a small thoracotomy, the ascending aorta and the main pulmonary artery were occluded with snares, and cardioplegic solution containing histamine was injected into the aortic root; viral constructs were delivered 3 to 5 minutes later followed by release of the occluders and rewarming. Four days later, homogeneous beta-galactosidase expression was detected throughout the ventricles of the normal hearts (average 77.3+/-9.0% [SEM] of left ventricular myocytes). At 1 and 3 weeks after transfection, immunostaining showed extensive restoration of delta-sarcoglycan as well as alpha- and beta-sarcoglycan proteins to the myocyte membranes, despite loss of beta-galactosidase expression at 3 weeks. Also, at 3 weeks after gene transfer, there was significantly less progression of left ventricular dysfunction assessed as percent change in fractional shortening compared with controls. CONCLUSIONS: This study demonstrates the feasibility of high efficiency in vivo myocardial gene transfer and shows application in improving the level of a deficient cardiac structural protein and cardiac function in CM hamsters. The approach should be useful for assessing effects of expressing other genes that influence the structure or function of the normal and failing heart.

Adenoviridae↗

PubMed2002

Fibulin-5/DANCE is essential for elastogenesis in vivo.

The elastic fibre system has a principal role in the structure and function of various types of organs that require elasticity, such as large arteries, lung and skin. Although elastic fibres are known to be composed of microfibril proteins (for example, fibrillins and latent transforming growth factor (TGF)-beta-binding proteins) and polymerized elastin, the mechanism of their assembly and development is not well understood. Here we report that fibulin-5 (also known as DANCE), a recently discovered integrin ligand, is an essential determinant of elastic fibre organization. fibulin-5-/- mice generated by gene targeting exhibit a severely disorganized elastic fibre system throughout the body. fibulin-5-/- mice survive to adulthood, but have a tortuous aorta with loss of compliance, severe emphysema, and loose skin (cutis laxa). These tissues contain fragmented elastin without an increase of elastase activity, indicating defective development of elastic fibres. Fibulin-5 interacts directly with elastic fibres in vitro, and serves as a ligand for cell surface integrins alphavbeta3, alphavbeta5 and alpha9beta1 through its amino-terminal domain. Thus, fibulin-5 may provide anchorage of elastic fibres to cells, thereby acting to stabilize and organize elastic fibres in the skin, lung and vasculature.

Animals↗

PubMed2002

Apoptosis and oncosis in the early progression of left ventricular dysfunction in the cardiomyopathic hamster.

The genetic defect in the cardiomyopathic (CM) hamster is a mutation in the glycoprotein-sarcoglycan (a component of the dystrophin-glycoprotein complex). Apoptosis has been identified in skeletal muscle of dystrophin-deficient mice, and therefore the role of myocardial apoptosis in relation to oncosis in causing myocardial necrosis was assessed at the onset of left ventricular (LV) dysfunction in CM hamsters. LV size and function were evaluated in normal and CM hamsters (CHF147 line) by echocardiography at 1, 2, 3, and 5 months (mo) of age. The decrease of LV fractional shortening was found to be most marked (45%) between 1 and 2 mo of age. Apop totic nuclei were identified at each time point using in situ end-labeling of DNA strand breaks (TUNEL), together with immunolabeling of myocytes; DNA fragmentation (laddering) and nuclear morphology were also assessed. Myocyte oncotic necrosis was assessed at 2 mo by Evans blue dye (EBD), wheat germ agglutinin, hematoxylin/eosin staining, and electron microscopy. Apoptotic nuclei were not detected in age-matched normal hamsters. In the CM hamsters apoptotic myocyte nuclei comprised an average of 0.041% of myocyte nuclei between 1 and 5 mo, an increase at 2 mo (to 0.076%) was not significant, and DNA laddering was not detected. The number of myocyte nuclei per unit area decreased by 32% between 1 and 2 mo, and in 2 mo old CM hamsters myocardial staining with EBD was positive in 9.82% of the myocardial cross sectional areas examined, most of which was consistent with sarcolemmal rupture and oncosis with inflammatory cell infiltration. It is concluded that myocyte oncosis provides the major mechanism for the decreased number of myocyte nuclei and the early decrease of cardiac function between 1 and 2 mo of age in the CM hamster, with only a small contribution of myocyte apoptosis.

Animals↗

PubMed2002

Dissolution rates of carbonated hydroxyapatite in hydrochloric acid.

Osteoclasts have been shown to dissolve efficiently and effectively the mineral phase of bone by locally controlling the environment surrounding the cell. Although this mineral phase has been identified and well characterized as carbonated hydroxyapatite, there is little understanding of the factors that affect the dissolution properties of this mineral phase. Mimicking the mechanism by which osteoclasts dissolve the mineral phase of bone may provide insight into methods for the decalcification of atherosclerotic mineral deposits in the vascular system. Accordingly, a detailed characterization of the effects of various chemical and mechanical parameters on the dissolution of carbonated hydroxyapatite mineral was investigated in this study. Increases in the mineral dissolution rate (2-10 times) were associated with increases in dissolving solution [H+], osmolality, temperature, and flow rate. Mineral dissolution rate increases (5-8 times) were associated with greater surface area of the mineral and mechanical agitation of the dissolving solution.

Biocompatible Materials↗

PubMed2002

Measurements of the solubilities and dissolution rates of several hydroxyapatites.

Calcium phosphate based materials, such as apatites, are increasingly being developed and used in implants for orthopedic and dental applications. Previous investigation of various calcium phosphate ceramics has demonstrated great variability in the solubility characteristics in solution between materials with similar stoichiometric composition. Therefore, in this study, the solubility and rate of dissolution of three apatite sources, BoneSource, Norian cranial repair system (CRS), and a sintered hydroxyapatite (Calcitite) are evaluated in a thermodynamically closed system. The measured solubility under physiological conditions (tris buffer solution, pH 7.4, 37 degrees C) of BoneSource, Norian CRS and Calcitite is 7.5, 7.4 and 1.4 ppm, respectively. Initial dissolution rates at 10 min of BoneSource, CRS, and Calcitite were 0.0465, 0.1589, and essentially 0 mg/min respectively. Solubility product constants at 37 degrees C were calculated to be 1.49 x 10(-35) for CRS, 1.19 x 10(-35) for BoneSource, and 2.92 x 10(-42) for Calcitite. The increased solubility of the BoneSource and Norian CRS materials over that of Calcitite is related to their poor crystallinity compared to sintered hydroxyapatite.

Biocompatible Materials↗

PubMed2002

ErbB2 is essential in the prevention of dilated cardiomyopathy.

Amplification of the gene encoding the ErbB2 (Her2/neu) receptor tyrosine kinase is critical for the progression of several forms of breast cancer. In a large-scale clinical trial, treatment with Herceptin (trastuzumab), a humanized blocking antibody against ErbB2, led to marked improvement in survival. However, cardiomyopathy was uncovered as a mitigating side effect, thereby suggesting an important role for ErbB2 signaling as a modifier of human heart failure. To investigate the physiological role of ErbB2 signaling in the adult heart, we generated mice with a ventricular-restricted deletion of Erbb2. These ErbB2-deficient conditional mutant mice were viable and displayed no overt phenotype. However, physiological analysis revealed the onset of multiple independent parameters of dilated cardiomyopathy, including chamber dilation, wall thinning and decreased contractility. Additionally, cardiomyocytes isolated from these conditional mutants were more susceptible to anthracycline toxicity. ErbB2 signaling in cardiomyocytes is therefore essential for the prevention of dilated cardiomyopathy.

Adult↗

PubMed2002

Clinical trials of the T-fluted (Ash Advantage) peritoneal dialysis catheter.

The Ash Advantage is a T-shaped peritoneal catheter with a single transabdominal tube joining to a tube lying against the parietal peritoneum. Segments with long flutes (grooves) serve as fluid ports rather than 1-mm diameter holes. The folded catheter is placed through the expandable Y-TEC Quill positioned peritoneoscopically, similar to the procedure for a conventional Tenckhoff catheter. In a clinical study, we placed 18 Ash Advantage ("Advantage") catheters, 8 in patients with prior hydraulic or infectious complications of Tenckhoff catheters and 10 in patients initiating peritoneal dialysis. Mean follow-up has been 8.4 months. Outflow rate for the Advantage catheters is uniformly higher than for Tenckhoff catheters at 220 +/- 100 mL/min for the first 5 minutes and 145 +/- 72 mL/min for the next 5 minutes, with outflow completed in 6 to 15 minutes. Variation of outflow volumes for similar exchanges in the same patient is +/- 3% to 5%, much less than with Tenckhoff catheters. Four catheters failed after placement, each for a different reason including outflow failure because of preexisting intraperitoneal adhesions, preexisting peritonitis failing to clear, tubing kink during placement, and catheter break after a freak accident. Life-table analysis of the production version of the catheter in study patients and 12 additional unselected patients indicates a 90% survival at 12 months. In long-term use, the fixed position of the cuffs of this catheter may avoid catheter extrusion, pericatheter hernias, and pericatheter leaks. Multiple fluted ports appear to diminish omental attachment. The catheter may be a useful alternative to conventional Tenckhoff catheters in patients at high risk of catheter failure or in standard peritoneal dialysis patients.

Catheters, Indwelling↗

PubMed2002

Impact of anesthesia on cardiac function during echocardiography in mice.

Anesthetics provide sedation and immobility facilitating echocardiography in mice, but influence cardiac function. We studied the effects of intraperitoneal and inhaled anesthetic agents on echocardiographic measurements. Mice were anesthetized with intraperitoneal tribromoethanol (TBE), ketamine-midazolam (K/M), ketamine-xylazine (K/X), or inhaled isoflurane (Isf), and echocardiographic parameters were assessed at 5, 10, 15, and 20 min. In C57BL/6N mice, Isf produced high initial heart rates (HR) that decreased to levels comparable to TBE at 15-20 min (approximately 450 beats/min) and the most stable percent fractional shortening (%FS) and end-diastolic dimension (EDD). With TBE, %FS initially was low, but increased comparable to Isf (approximately 45%) at 15 min. K/M produced similar time trends but lower absolute values compared with TBE for all parameters. K/X produced cardiac depression evidenced by low HR and %FS, and increased EDD. Isf was the most reproducible in repeat studies at 12 days. In C57BL/6J compared with C57BL/6N mice, K/M produced higher HR, and %FS and TBE produced smaller EDD. In conclusion, anesthetic agent, timing of echocardiographic measurements, and genetic background are all critical variables during echocardiography in mice.

Administration, Inhalation↗

PubMed2002

Dilated cardiomyopathy: concepts derived from gene deficient and transgenic animal models.

Genetic forms of human dilated cardiomyopathy (DCM) are briefly discussed, and a variety of animal models of genetic DCM are presented, some of which are caused by the gene mutations that also cause DCM in humans. The forms of DCM related to mutations or deletion of genes coding for extrasarcomeric or intrasarcomeric proteins, as well as to overexpression or knockout of genes in the beta-adrenergic signaling pathway, are included. Finally, novel approaches to treatment in experimental animal models are discussed, including double transgenesis and newer recombination methods, as well as in vivo somatic gene transfer which, based on initial experiments in animals, seems likely to find eventual application in human cardiac failure.

Animals↗

PubMed2001

Bayesian analysis of systems with random chemical composition: renormalization-group approach to Dirichlet distributions and the statistical theory of dilution.

We investigate the statistical properties of systems with random chemical composition and try to obtain a theoretical derivation of the self-similar Dirichlet distribution, which is used empirically in molecular biology, environmental chemistry, and geochemistry. We consider a system made up of many chemical species and assume that the statistical distribution of the abundance of each chemical species in the system is the result of a succession of a variable number of random dilution events, which can be described by using the renormalization-group theory. A Bayesian approach is used for evaluating the probability density of the chemical composition of the system in terms of the probability densities of the abundances of the different chemical species. We show that for large cascades of dilution events, the probability density of the composition vector of the system is given by a self-similar probability density of the Dirichlet type. We also give an alternative formal derivation for the Dirichlet law based on the maximum entropy approach, by assuming that the average values of the chemical potentials of different species, expressed in terms of molar fractions, are constant. Although the maximum entropy approach leads formally to the Dirichlet distribution, it does not clarify the physical origin of the Dirichlet statistics and has serious limitations. The random theory of dilution provides a physical picture for the emergence of Dirichlet statistics and makes it possible to investigate its validity range. We discuss the implications of our theory in molecular biology, geochemistry, and environmental science.

Algorithms↗

PubMed2001

The cardiac-specific nuclear delta(B) isoform of Ca2+/calmodulin-dependent protein kinase II induces hypertrophy and dilated cardiomyopathy associated with increased protein phosphatase 2A activity.

The delta isoform of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) predominates in the heart. To investigate the role of CaMKII in cardiac function, we made transgenic (TG) mice that express the nuclear delta(B) isoform of CaMKII. The expressed CaMKIIdelta(B) transgene was restricted to the myocardium and highly concentrated in the nucleus. Cardiac hypertrophy was evidenced by an increased left ventricle to body weight ratio and up-regulation of embryonic and contractile protein genes including atrial natriuretic factor, beta-myosin heavy chain, and alpha-skeletal actin. Echocardiography revealed ventricular dilation and decreased cardiac function, which was also observed in hemodynamic measurements from CaMKIIdelta(B) TG mice. Surprisingly, phosphorylation of phospholamban at both Thr(17) and Ser(16) was significantly decreased in the basal state as well as upon adrenergic stimulation. This was associated with diminished sarcoplasmic reticulum Ca(2+) uptake in vitro and altered relaxation properties in vivo. The activity and expression of protein phosphatase 2A were both found to be increased in CaMKII TG mice, and immunoprecipitation studies indicated that protein phosphatase 2A directly associates with CaMKII. Our findings are the first to demonstrate that CaMKII can induce hypertrophy and dilation in vivo and indicate that compensatory increases in phosphatase activity contribute to the resultant phenotype.

Adrenergic beta-Agonists↗