Mapping the Coulomb Environment in Interference-Quenched Ballistic Nanowires

The conductance of semiconductor nanowires is strongly dependent on their electrostatic history because of the overwhelming influence of charged surface and interface states on electron confinement and scattering. We show that InAs nanowire field-effect transistor devices can be conditioned to suppress resonances that obscure quantized conduction thereby revealing as many as six sub-bands in the conductance spectra as the Fermi-level is swept across the sub-band energies. The energy level spectra extracted from conductance, coupled with detailed modeling shows the significance of the interface state charge distribution revealing the Coulomb landscape of the nanowire device. Inclusion of self-consistent Coulomb potentials, the measured geometrical shape of the nanowire, the gate geometry and nonparabolicity of the conduction band provide a quantitative and accurate description of the confinement potential and resulting energy level structure. Surfaces of the nanowire terminated by HfO₂ are shown to have their interface donor density reduced by a factor of 30 signifying the passivating role played by HfO₂.

A rabbit model of cerebral microembolic signals for translational research: preclinical validation for aspirin and clopidogrel

Essentials Microembolic signal (MES) is an independent predictor of stroke risk in patients. A rabbit model of cerebral microembolic signals was established. Therapeutic efficacy was demonstrated for aspirin and clopidogrel on microembolic signals. Potential translational value of this preclinical model of MES was demonstrated.

SUMMARY

Objectives Cerebral microembolic signals (MESs) detected by transcranial Doppler (TCD) ultrasound constitute an independent predictor of stroke risk and prognosis. The aim of this study was to develop a novel preclinical model of MESs to facilitate translational research. Methods A clinical TCD ultrasound machine was used to detect MESs in the cerebral circulation of New Zealand White rabbits. Technical feasibility was assessed for the measurement of MESs in the middle cerebral artery (MCA) by TCD. FeCl3 -induced carotid arterial thrombosis was optimized for the generation of endogenous microemboli. Ascending doses of two antithrombotic agents (aspirin and clopidogrel) were evaluated individually and in combination for their effects on both arterial thrombosis and MESs in a 30% FeCl3 -induced carotid arterial thrombosis model, along with ex vivo functional assays. Results Dose-dependent FeCl3 -induced arterial thrombosis studies showed that 30% FeCl3 resulted in the most consistent and reproducible MESs in the MCA (3.3 ± 0.7 MESs h(-1) ). Ascending-dose studies showed that the effective doses for 50% inhibition (ED50 ) of thrombus formation, based on integrated blood flow and thrombus weight, respectively, were 3.1 mg kg(-1) and 4.2 mg kg(-1) orally for aspirin, and 0.3 mg kg(-1) and 0.28 mg kg(-1) orally for clopidogrel. The ED50 values for MES incidence were 12.7 mg kg(-1) orally for aspirin, and 0.25 mg kg(-1) orally for clopidogrel. Dual treatment with aspirin (5 mg kg(-1) ) and clopidogel (0.3 mg kg(-1) ) resulted in significant reductions in cerebral MESs (P < 0.05) as compared with monotherapy with either agent. Conclusions Our study demonstrated the successful establishment of the MES model in rabbits, and it may provide translational value for MESs and ischemic stroke research.

Pathophysiologic bases for adjunctive therapies in the treatment and secondary prevention of acute myocardial infarction

Postmyocardial infarction (MI) survival has been steadily improving. This improvement has been due, in part, to the actions of the adjunctive medical therapies for the treatment of MI. Aspirin, beta blockers, angiotensin-converting enzyme (ACE) inhibitors, and lipid-lowering agents have been shown to improve survival in the treatment and secondary prevention of MI. Nitrates have beneficial effects as well. These medications complement the reperfusion strategies through different mechanisms. Other adjunctive medical therapies, namely magnesium, antiarrhythmic agents, and calcium-channel blockers, have not been shown to improve mortality with routine post-MI use despite their theoretical benefits.

Conditional gene targeting of connexin43: exploring the consequences of gap junction remodeling in the heart

Abnormalities in cardiac gap junction expression have been postulated to contribute to arrhythmias and ventricular dysfunction. We investigated the role of cardiac gap junctions by generating a heart-specific conditional knock-out (CKO) of connexin43 (Cx43), the major cardiac gap junction protein. While the Cx43 CKO mice have normal heart structure and contractile function, they die suddenly from spontaneous ventricular arrhythmias. Because abnormalities in gap junction expression in the diseased heart can be focal, we also generated chimeric mice formed from Cx43-null embryonic stem (ES) cells and wildtype recipient blastocysts. Heterogeneous Cx43 expression in the chimeric mice resulted in conduction defects and depressed contractile function. These novel genetic murine models of Cx43 loss of function in the adult mouse heart define gap junctional abnormalities as a key molecular feature of the arrhythmogenic substrate and an important factor in heart dysfunction.

Tissue factor deficiency causes cardiac fibrosis and left ventricular dysfunction

Exposure of blood to tissue factor (TF) activates the extrinsic (TF:FVIIa) and intrinsic (FVIIIa:FIXa) pathways of coagulation. In this study, we found that mice expressing low levels of human TF ( approximately 1% of wild-type levels) in an mTF(-/-) background had significantly shorter lifespans than wild-type mice, in part, because of spontaneous fatal hemorrhages. All low-TF mice exhibited a selective heart defect that consisted of hemosiderin deposition and fibrosis. Direct intracardiac measurement demonstrated a 30% reduction (P < 0.001) in left ventricular function in 8-month-old low-TF mice compared with age-matched wild-type mice. Mice expressing low levels of murine FVII ( approximately 1% of wild-type levels) exhibited a similar pattern of hemosiderin deposition and fibrosis in their hearts. In contrast, FIX(-/-) mice, a model of hemophilia B, had normal hearts. Cardiac fibrosis in low-TF and low-FVII mice appears to be caused by hemorrhage from cardiac vessels due to impaired hemostasis. We propose that TF expression by cardiac myocytes provides a secondary hemostatic barrier to protect the heart from hemorrhage.

Heterogeneous expression of Gap junction channels in the heart leads to conduction defects and ventricular dysfunction

BACKGROUND

- Heterogeneous remodeling of gap junctions is observed in many forms of heart disease. The consequent loss of synchronous ventricular activation has been hypothesized to result in diminished cardiac performance. To directly test this hypothesis, we designed a murine model of heterogeneous gap junction channel expression. Methods and Results-- We generated chimeric mice formed from connexin43 (Cx43)-deficient embryonic stem cells and wild-type or genetically marked ROSA26 recipient blastocysts. Chimeric mice developed normally, without histological evidence of myocardial fibrosis or hypertrophy. Heterogeneous Cx43 expression resulted in conduction defects, however, as well as markedly depressed contractile function. Optical mapping of chimeric hearts by use of voltage-sensitive dyes revealed highly irregular epicardial conduction patterns, quantified as significantly greater negative curvature of the activation wave front (-1.86+/-0.40 mm in chimeric mice versus -0.86+/-0.098 mm in controls; P<0.01; n=6 for each group). Echocardiographic studies demonstrated significantly reduced fractional shortening in chimeric mice (26.6+/-2.3% versus 36.5+/-1.6% in age-matched 129/SvxC57BL/6F1 wild-type controls; P<0.05).

CONCLUSIONS

- These data suggest that heterogeneous Cx43 expression, by perturbing the normal pattern of coordinated myocardial excitation, may directly depress cardiac performance.

Predicting plaque rupture: enhancing diagnosis and clinical decision-making in coronary artery disease

Atherosclerosis is the process underlying coronary artery disease, myocardial infarction and cerebrovascular disease and is a leading cause of morbidity and mortality in industrialized countries. The atherosclerotic plaque is often indolent and progressive and may destabilize without warning. Components of the atherosclerotic plaque, including structural, cellular and molecular characteristics, determine its vulnerability to rupture. The imaging techniques currently available utilize invasive and non-invasive methods to characterize coronary artery stenoses. Detection, however, usually occurs late in the course of disease after symptoms have presented. Much effort has recently been directed at early detection and in defining markers of atherosclerotic disease. Our challenge for the future is to find non-invasive imaging modalities that can predict plaque vulnerability before irreversible damage has occurred. Through early detection and a targeted treatment strategy we hope to reduce the burden of ischemic heart disease.

Conduction slowing and sudden arrhythmic death in mice with cardiac-restricted inactivation of connexin43

Cardiac arrhythmia is a common and often lethal manifestation of many forms of heart disease. Gap junction remodeling has been postulated to contribute to the increased propensity for arrhythmogenesis in diseased myocardium, although a causative role in vivo remains speculative. By generating mice with cardiac-restricted knockout of connexin43 (Cx43), we have circumvented the perinatal lethal developmental defect associated with germline inactivation of this gap junction channel gene and uncovered an essential role for Cx43 in the maintenance of electrical stability. Mice with cardiac-specific loss of Cx43 have normal heart structure and contractile function, and yet they uniformly (28 of 28 conditional Cx43 knockout mice observed) develop sudden cardiac death from spontaneous ventricular arrhythmias by 2 months of age. Optical mapping of the epicardial electrical activation pattern in Cx43 conditional knockout mice revealed that ventricular conduction velocity was significantly slowed by up to 55% in the transverse direction and 42% in the longitudinal direction, resulting in an increase in anisotropic ratio compared with control littermates (2.1+/-0.13 versus 1.66+/-0.06; P:<0.01). This novel genetic murine model of primary sudden cardiac death defines gap junctional abnormalities as a key molecular feature of the arrhythmogenic substrate.

Thrombosis and coagulation abnormalities in the acute coronary syndromes

The acute coronary syndromes, that include unstable angina, acute myocardial infarction, and many cases of sudden cardiac death, exact a considerable price on society in terms of mortality, morbidity, and health care costs. The coronary atherosclerotic lesion is often an indolent and progressive entity that can destabilize causing an acute syndrome with or without warning. The majority of acute coronary syndromes result from events such as rupture or disruption of the atherosclerotic plaque with intracoronary thrombosis and ischemia of the distal myocardium as a result. Advances in our understanding of the process underlying the acute coronary syndromes has allowed for the identification of targets and rational therapeutic strategies for the prevention and treatment of these syndromes. Many of these therapeutic strategies involve the reversal of prethrombotic forces that often coexist with coronary atherosclerosis. Even with recent advances in our approach to atherosclerosis, intracoronary thrombosis, and the resulting acute coronary syndromes, an unacceptably high event rate persists after these syndromes. Further advances in the prevention and treatment of coronary atherosclerosis and its thrombotic complications depends on a more thorough understanding of the biology of the atherosclerotic plaque and the factors which influence its stability.

Intracellular calcium release channel expression during embryogenesis

The release of intracellular calcium (Ca2+) via either inositol 1,4, 5-trisphosphate receptors (IP3R) or ryanodine receptors (RyR) activates a wide variety of signaling pathways in virtually every type of cell. In the present study we demonstrate that at early stages of development IP3R mRNA and functional IP3-gated Ca2+ release channels are widely expressed in virtually all tissues in murine embryos. As organogenesis proceeds, more specialized RyR channels are expressed in many cell types and the triggering mechanisms for intracellular Ca2+ release become more diverse to include IP3-dependent and voltage-dependent and Ca2+-induced Ca2+ release. As development proceeds virtually all cell types continue to express IP3R channels but in excitable cells including skeletal and cardiac muscles the major Ca2+ release channels are RyRs. This developmental switch from predominantly IP3-mediated to both IP3-mediated and IP3-independent pathways for intracellular Ca2+ release is consistent with data showing that IP3R plays an important regulatory role in cellular proliferation and apoptosis, whereas RyR is required for other cellular functions including muscle contraction.

Pathophysiology and clinical significance of atherosclerotic plaque rupture

Atherosclerotic plaque rupture and resulting intracoronary thrombosis are thought to account for most acute coronary syndromes. These syndromes include unstable angina, non-Q-wave myocardial infarction (MI) and Q-wave MI. In addition, many cases of sudden cardiac death may be attributable to atherosclerotic plaque disruption and its immediate complications. Our understanding of the atherosclerotic process and the pathophysiology of plaque disruption has advanced remarkably. Despite these advances, event rates after acute coronary syndromes remain unacceptably high. This review will focus on the pathophysiology underlying atherosclerotic plaque development, the sequellae of coronary plaque rupture, and current therapies designed to treat the acute coronary syndromes. It is hoped that as our understanding of the atherosclerotic plaque improves, treatment strategies for the acute coronary syndromes will advance.

Role of inositol 1,4,5-trisphosphate receptors in regulating apoptotic signaling and heart failure

The inositol 1,4,5-trisphosphate receptor (IP3R) is an endoplasmic reticular calcium release channel found in most cell types. Calcium signaling mediated by IP3Rs regulates a wide variety of physiological processes, including smooth muscle contraction, immune function, and fertility. We have focused on the role of the IP3R in programmed cell death and the regulation of IP3R levels in heart failure, a condition shown to be associated with cardiomyocyte apoptosis. During end-stage human heart failure, we have demonstrated that type 1 IP3R (IP3R1) mRNA and protein levels are up-regulated, in contrast to other cardiac calcium regulatory proteins, such as the type 2 ryanodine receptor (RYR2) and type IIa sarcoplasmic reticulum calcium adenosine triphosphatase (SERCA2), which are down-regulated. These data suggest that altered calcium channel expression may contribute to the defects in calcium homeostasis during heart failure. Furthermore, regulation of the IP3R may have implications for the survival of cardiac myocytes. Data from our laboratory have linked IP3R expression with susceptibility to apoptosis. IP3R-deficient T cells are resistant to apoptosis induced by dexamethasone, T cell receptor stimulation, ionizing radiation, and Fas. These findings suggest that intracellular calcium release via IP3Rs is a critical mediator of apoptosis. Thus the IP3R, which is up-regulated during human heart failure, may play a role in cardiomyocyte apoptosis and therefore in the pathophysiology of heart failure.

Revascularization in advanced stable coronary artery disease

Identifying patients with stable coronary artery disease (CAD) who benefit from revascularization is a challenge for the clinician. Based on survival data, we have devised a guide to help the clinician decide which patients with advanced stable CAD should be treated more aggressively with revascularization and which patients may be followed with medical therapy alone. Survival data support the recommendation of coronary artery bypass grafting (CABG) when at least two of the following factors are present: advanced CAD, left ventricular (LV) dysfunction and significant ischemia. For patients with advanced CAD and LV dysfunction, or left main coronary artery disease, CABG remains the treatment of choice. In patients with normal LV function, but advanced CAD and significant ischemia, percutaneous transluminal coronary angioplasty (PTCA) and CABG appear to provide similar survival outcomes. While CABG is more invasive and is associated with a longer recovery period, PTCA is associated with more repeat revascularization procedures on follow-up than CABG. Thus, while the recommendation for revascularization in advanced stable CAD is made based on survival data, in some patients the choice of revascularization procedure may depend on the needs and preferences of the individual patient.

Nontraumatic intramural hematoma of the duodenum complicating warfarin therapy

A 74-year-old man receiving chronic anticoagulant therapy presented with symptoms of acute small bowel obstruction. He was subsequently found to have an intramural hematoma of the duodenum. Early noninvasive diagnosis was possible using computed tomography. Conservative therapy proved successful in allowing resolution of obstructive symptoms. This case illustrates the effectiveness of a conservative approach to intramural hematoma of the duodenum, even in patients requiring anticoagulation.

Management of stable coronary artery disease

Options for the treatment of multivessel coronary artery disease include medical therapy and revascularization with either coronary artery bypass grafting (CABG) or percutaneous transluminal coronary angioplasty (PTCA). CABG has been shown to prolong survival in patients with left main coronary disease or when at least two of the following factors are present: extensive coronary artery disease, significant ischemia as shown on stress testing and left ventricular dysfunction. In patients with extensive coronary artery disease but normal left ventricular function, either PTCA or CABG may be used initially without adversely affecting rates of survival. However, patients undergoing angioplasty have a higher rate of repeat revascularization procedures than those treated with bypass. The complex interplay of the various risks and benefits of medical therapy, angioplasty or bypass in the treatment of coronary artery disease requires an individualized approach to therapy and careful patient education.

Decreased inotropic but relatively preserved relaxation response to cyclic adenosine monophosphate-dependent agents in myopathic human myocardium

BACKGROUND

Increased intracellular concentrations of cyclic adenosine monophosphate (AMP) stimulate a positive inotropic and lusitropic response in healthy myocardial tissue. Heart failure results in an attenuated inotropic response to cyclic AMP-dependent agents. This study compares the inotropic versus relaxation response to cyclic AMP-dependent and cyclic AMP-independent agents in myocardium from patients with end-stage heart failure and control patients without heart failure.

METHODS AND RESULTS

Fifty-four control and 59 myopathic human ventricular trabeculae, 1 mm or less in diameter were placed in physiologic saline, 2.5 mM Ca2+, and stretched to the length at which maximal isometric force developed at 30 degrees C, 0.33 Hz. Dose-response curves plotted as percentage change from baseline versus concentration of drug were determined for acetylstrophanthidin, isoproterenol, isobutylmethylxanthine, and milrinone. Acetylstrophanthidin, a cyclic AMP-independent agent, showed similar increases in peak tension relative to baseline over the entire dose range tested for both control and myopathic heart muscle; its effect on relaxation of control and failing cardiac muscle was equivalent over the dose range tested. In contrast, the inotropic actions of the cyclic AMP-dependent agents, isoproterenol and the phosphodiesterase inhibitors, were significantly decreased in myopathic muscle compared with control muscle, but effects on relaxation in the control and myopathic groups remained relatively preserved.

CONCLUSIONS

A relatively preserved relaxant effect is associated with the cyclic AMP-dependent agents, despite significant diminution of their inotropic effects. Thus, in advanced heart failure, patients may continue to benefit from the lusitropic effects of the cyclic AMP-dependent agents, even when the inotropic effects of these agents are severely attenuated.

Abnormal myocardial calcium handling in the early stage of adriamycin cardiomyopathy

Metabolic changes have been shown to precede mechanical abnormalities in the early stages of adriamycin cardiotoxicity. This study examines the early changes in calcium homeostasis and their mechanical implications in a model of adriamycin cardiomyopathy. Hearts isolated from control and adriamycin-treated rats were coronary-perfused and isovolumic left ventricular (LV) pressure, coronary perfusion pressure and calcium transients from aequorin-loaded cardiomyocytes were recorded. Treated rats received three injections of adriamycin (6 mg/kg) for a period of 1 week. They were sacrificed for experiments 1-2 or 4-5 weeks after the final injection. The LV systolic and end-diastolic pressures were similar in both groups at varied external calcium concentrations (0.5-2.0 mM). However, systolic levels of myoplasmic calcium were substantially higher in the adriamycin-treated hearts, the difference being less at higher external calcium concentrations. Similar responses in both groups to paired pulse stimulation, increased stimulation frequency and caffeine (0.5-2.0 mM) were observed. However, adriamycin-treated hearts exhibited a smaller rise in LV developed pressure, as well as in systolic and diastolic calcium levels, in response to elevated coronary perfusion pressure. The elevated intracellular systolic calcium level is suggestive of an early but persistent effect of adriamycin on the calcium release channels of the sarcoplasmic reticulum. That the elevated systolic myoplasmic calcium levels are not accompanied by an increase in inotropy suggests a decrease in myofibrillar calcium sensitivity in this model of the early stage of adriamycin cardiomyopathy.

Indications and advantages of laparoscopy-assisted colon resection for carcinoma in elderly patients

The controversy about laparoscopy assisted colectomy for cancer is based on doubt about performing a radical resection and adequate histopathological staging. Therefore, we selected a group of patients who could profit from the accepted benefits of the technique, while avoiding its uncontrolled outcome. We operated on patients with colorectal cancer with distant metastasis and on patients over 70 years old and American Society of Anesthesia (ASA) III-IV with a high operative risk with standard surgery. The results for the first 18 patients demonstrated the following: (a) the size of the surgical specimen and the number of lymph nodes were similar to those in standard surgery; (b) no mortality and very low morbidity occurred despite the patients' advanced age, debilitated condition, and comorbid diseases; (c) minor postoperative complications occurred in five of 18 patients; (d) the hospital stay was 6-7 days for nonmetastatic patients and 9-12 days for metastatic patients; (e) the 1-year survey revealed a relapse in only one patient 9 months after the first operation.

[Diverticula of the small intestine. Presentation of 2 new cases and review of the literature]

Diverticuli of the small intestine are a rare, usually asymptomatic affectation. These diverticuli are acquired by pulsion and are the consequence of previous intestinal dyskinesia. Acute complications of jejunoileal diverticulosis are: diverticulitis, perforation, as in one of our cases, hemorrhage and obstruction; chronic complications are: megaloblastic anemia, malabsorption syndrome and steatorrhea. The preoperative diagnosis at the present poses great difficulties and surgical treatment is only indicated for complications.

[Increase of bile acid reabsorption following total small intestine resection in the rat]

Bile salts undergo an enterohepatic circulation. The relative distribution of labelled cholic acid in portal blood, enterocytes, intestinal contents and feces, following intravenous injection of (carboxylic-14C) cholic acid, can be considered as an indication of the absorptive capacity of the epithelium cells. Seven days after a massive small intestinal resection (60-80 cm), the animal weight and the bile salt absorption were significantly decreased. Nevertheless, thirty days after the operation, weight and radioactivities reached the values found in the controls: in portal and cava blood, liver, intestinal contents and feces. An increase of the absorptive capacity of the intestinal epithelial cells was also observed.