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Biomedical subjects

James D Marsh

Publications and source records attributed to James D Marsh.

18 recordsLinked to original sources
PubMed2006

Vascular calcium channels and high blood pressure: pathophysiology and therapeutic implications.

Long-lasting Ca(2+) (Ca(L)) channels of the Ca(v)1.2 gene family are heteromultimeric structures that are minimally composed of a pore-forming alpha(1C) subunit and regulatory beta and alpha(2)delta subunits in vascular smooth muscle cells. The Ca(L) channels are the primary pathways for voltage-gated Ca(2+) influx that trigger excitation-contraction coupling in small resistance vessels. Notably, vascular smooth muscle cells of hypertensive rats show an increased expression of Ca(L) channel alpha(1C) subunits, which is associated with elevated Ca(2+) influx and the development of abnormal arterial tone. Indeed, blood pressure per se appears to promote Ca(L) channel expression in small arteries, and even short-term rises in pressure may alter channel expression. Membrane depolarization has been shown to be one stimulus associated with elevated blood pressure that promotes Ca(L) channel expression at the plasma membrane. Future studies to define the molecular processes that regulate Ca(L) channel expression in vascular smooth muscle cells will provide a rational basis for designing antihypertensive therapies to normalize Ca(L) channel expression and the development of anomalous vascular tone in hypertensive pathologies.

Animals↗
PubMed2006

Detection of carotid stenosis in African Americans with ischemic heart disease.

OBJECTIVES: This study was conducted to define the frequency of internal carotid stenosis in African American patients with ischemic heart disease (IHD). METHODS: We recruited 101 African American patients with IHD from a university medical center for carotid duplex examination. RESULTS: The frequency of >30%, >50%, and >70% stenosis was 21%, 11%, and 5%, respectively. Age >60 years (21% vs 3%, P < .01) and diabetes mellitus (22% vs 5%, P < .01) were predictors of unilateral stenosis of >50% and remained significant on multivariate testing. CONCLUSION: African American patients with established IHD have higher rates of extracranial carotid stenosis than community dwelling African American subjects and comparable rates with other populations.

Black or African American↗
PubMed2005

Ca2+ influx-induced sarcoplasmic reticulum Ca2+ overload causes mitochondrial-dependent apoptosis in ventricular myocytes.

Increases in Ca2+ influx through the L-type Ca2+ channel (LTCC, Cav1.2) augment sarcoplasmic reticulum (SR) Ca2+ loading and the amplitude of the cytosolic Ca2+ transient to enhance cardiac myocyte contractility. Our hypothesis is that persistent increases in Ca2+ influx through the LTCC cause apoptosis if the excessive influx results in SR Ca2+ overload. Feline ventricular myocytes (VMs) in primary culture were infected with either an adenovirus (Ad) containing a rat Cav1.2 beta2a subunit-green fluorescent protein (GFP) fusion gene (Adbeta2a) to increase Ca2+ influx or with AdGFP as a control. Significantly fewer beta2a-VMs (21.4+/-5.6%) than GFP-VMs (99.6+/-1.7%) were viable at 96 hours. A fraction of beta2a-VMs (20.8+/-1.8%) contracted spontaneously (SC-beta2a-VMs), and viability was significantly correlated with the percentage of SC-beta2a-VMs. Higher percentages of apoptotic nuclei, DNA laddering, and cytochrome C release were detected in beta2a-VMs. This apoptosis was prevented with pancaspase or caspase-3 or caspase-9 inhibitors. L-type calcium current (I(Ca-L)) density was greater in beta2a-VMs (23.4+/-2.8 pA/pF) than in GFP-VMs (7.6+/-1.6 pA/pF). SC-beta2a-VMs had higher diastolic intracellular Ca2+ (Indo-1 ratio: 1.1+/-0.1 versus 0.7+/-0.03, P<0.05) and systolic Ca2+ transients (1.89+/-0.27 versus 0.80+/-0.08) than GFP-VMs. Inhibitors of Ca2+ influx, SR Ca2+ uptake and release, mitochondrial Ca2+ uptake, mitochondrial permeation transition pore, calpain, and Bcl-2-associated X protein protected beta2a-VMs from apoptosis. These results show that persistent increases in Ca2+ influx through the I(Ca-L) enhance contractility but lead to apoptosis through a mitochondrial death pathway if SR Ca2+ overload is induced.

Animals↗
PubMed2005

The L-type calcium channel alpha 1C subunit gene undergoes extensive, uncoordinated alternative splicing.

The alpha1C subunit is the pore-forming protein for the L-type calcium channel. Previous studies indicate that there is possible tissue-specific alternative splicing of this gene. In this study we cloned the entire open reading frame of the alpha1C subunit cDNA from adult rat cardiac myocytes in a single piece (6.64 kb). Using 75 positive clones that were identified by restriction enzyme mapping, we tested the alternative splicing patterns of the Ca(v) 1.2 gene that encodes the alpha1C subunit protein and focused on five loci: IS6, post-IS6, IIIS2, IVS3, and the c-terminus. The results indicate that: (1) alternative splicing occurs in most of the loci, giving rise to two or three different isoforms at those sites; (2) there is a predominant form for each splicing site, (3) there does not appear to be consistent coordination of splicing at multiple loci of this gene. Alternative splicing is not tissue-specific in most regions.

Alternative Splicing↗
PubMed2005

Acute actions of testosterone on contractile function of isolated rat ventricular myocytes.

Variation between the sexes in cardiac function have been established. The extent to which sex hormones are responsible for these differences is unclear. The current study was designed to determine whether testosterone acts acutely to enhance contractility of cultured rat ventricular myocytes. Following a 24-h treatment with testosterone (1 microM), isolated rat ventricular myocytes display a 21% increase (P < 0.01) in peak shortening and an 18% decrease (P < 0.02) in time to peak shortening. In accordance with this change, testosterone treatment produced an 18% decline (P < 0.002) in the time to relengthening when compared to vehicle-treated controls. These results provide the first evidence that short-term androgen exposure acts directly to stimulate contractility of isolated rat ventricular myocytes and thus may play a role in regulating cardiac performance in males and thereby contribute to sex differences in cardiac function.

Animals↗
PubMed2005

High glucose inhibits apoptosis induced by serum deprivation in vascular smooth muscle cells via upregulation of Bcl-2 and Bcl-xl.

Apoptosis plays a critical role in normal vascular development and atherosclerosis. To test the hypothesis that diabetic vasculopathy may be due in part to altered apoptosis pathways, we investigated the effects of high glucose treatment on serum withdrawal-induced apoptosis, expression of Bcl-2 family members, and inhibitor of apoptosis protein (IAP)-1 in vascular smooth muscle cells (VSMCs). Treatment with a high concentration of glucose (22 mmol/l) significantly attenuated apoptosis in response to serum withdrawal in cultured rat VSMCs compared with cells treated with a normal glucose concentration (5.5 mmol/l). This attenuation was accompanied by a significant decrease in the caspase-3 activity in comparison with the normal glucose group. Furthermore, exposure of VSMCs to high glucose markedly increased the abundance of Bcl-2 and Bcl-xl mRNAs compared with treatment with normal glucose, while expression of bax and IAP-1 mRNA remained unchanged. Our results suggest that high glucose suppresses serum withdrawal-induced apoptosis in VSMCs by upregulating expression of Bcl-2 and Bcl-xl, suggesting that enhanced expression of antiapoptotic proteins may play an important role in the development of macrovascular complications in diabetes.

Animals↗
PubMed2004

Phosphorylation and dephosphorylation of calsequestrin on CK2-sensitive sites in heart.

Calsequestrin (CSQ) concentrates in junctional sarcoplasmic reticulum (SR) where it functions in regulation of Ca2+ release. When purified from heart tissue, cardiac CSQ contains phosphate on a cluster of C-terminal serine residues, but little is known about the cellular site of kinase action, and the identity of the kinase remains uncertain. To determine basic features of the phosphorylation, we examined the reaction in canine heart preparations. CSQ phosphorylation was observed in [32P]metabolically-labeled heart cells after adenoviral overexpression, and its constitutive phosphorylation was limited to a CK2-sensitive C-terminal serine cluster. The CSQ kinase was oriented intralumenally, as was CSQ, inside membrane vesicles, such that exposure to each required detergent permeabilization. Yet even after detergent permeabilization, CSQ was phosphorylated much less efficiently by protein kinase CK2 in cardiac microsomes than was purified CSQ. Reduced phosphorylation was strongly dependent upon protein concentration, and phosphorylation time courses revealed a phosphatase activity that occurred constitutively as phosphorylated substrate accumulates. Evidence of selective dephosphorylation of CSQ glycoforms in heart homogenates was also seen by mass spectrometry analysis. Molecules with greater mannose content, a feature of early secretory pathway compartments, were more highly phosphorylated, while greater dephosphorylation was apparent in more distal compartments. Taken together, the analyses of CSQ phosphorylation in heart suggest that a constitutive process of phosphate turnover occurs for cardiac CSQ perhaps associated with its intracellular transport.

Adenoviridae↗
PubMed2004

Pathobiology of atherosclerosis--a brief review.

Considerable progress has been made recently in understanding the pathobiology of atherosclerosis. To a significant degree it is an inflammatory disease of the vessel wall. Progression of atherosclerosis or its stabilization reflects the tension between cytokines and effectors that play both an inhibiting and a facilitating role in the progression of atherosclerosis, including platelet-derived growth factor (PDGF), interleukin-1, tumor necrosis factor (TNF) -alpha, and MCP-1. The response to injury model remains central to our understanding of atherogenesis. Numerous factors may initiate endothelial injury, including mechanical factors (hypertension and high shear stress in the artery), homocysteine, oxidized low-density lipoprotein (LDL), possibly infectious agents such as Chlamydia, viruses, and toxins such as nicotine. These factors lead to endothelial cells' increasing expression of receptors for LDL and increased adherence of monocytes and macrophages and T cells. Progression of atherosclerosis can lead to the development of a plaque that is vulnerable to rupture and that would then produce an acute coronary syndrome. In addition to standard biomarkers and angiographic approaches for detecting plaque rupture, novel diagnostic approaches are under development, including near infrared spectroscopy, catheter-based thermography, and optical coherence tomography. Our better understanding of the atherosclerotic plaque provides multiple opportunities for interdicting arterial injury, and the response to it.

Arteriosclerosis↗
PubMed2004

Gonadectomy alters myosin heavy chain composition in isolated cardiac myocytes.

Sex differences in cardiac function have been identified. Studies suggest that the presence of testosterone in males may contribute to the observed differences in cardiac function. Our laboratory has shown previously that testosterone treatment of gonadectomized adult male rats enhances contractility of isolated rat ventricular myocytes. In this study we tested the hypothesis that gonadectomy and hormone replacement influences contractility by altering myosin heavy chain (MHC) composition. To test this hypothesis we analyzed myosin isoform expression in ventricular myocytes isolated from castrated rats displaying a decrease in myocyte contractile velocity and compared them to castrates treated with testosterone that displayed normal myocyte shortening velocity. Sixteen weeks after castration isolated rat ventricular myocytes displayed a 90% (p < 0.001) decline in MHC-alpha mRNA levels and over a twofold (p < 0.01) increase in MHC-beta transcripts when compared to sham-operated controls. Consistent with these changes we also observed a substantial decline in the ratio of MHC-alpha to MHC-beta protein expression. A reversal in myosin heavy chain composition was achieved following testosterone replacement. These studies provide the first direct evidence that testosterone replacement in gonadectomized animals enhances contractility via transcriptional and translational control of myosin heavy chain composition in isolated rat ventricular myocytes. The influence of testosterone on MHC composition in males may underlie some of the observed sex differences in cardiac function.

Animals↗
PubMed2003

Gonadectomy of adult male rats reduces contractility of isolated cardiac myocytes.

Sex-related differences in cardiac function have been well documented. The extent to which sex hormones are responsible for these differences is unclear. The current study was designed to determine whether castration and androgen replacement resulted in changes in functional expression of genes encoding the L-type calcium channel and Na/Ca exchanger in isolated rat ventricular myocytes. Sixteen weeks of castration produced a 50% decline in dihydropyridine receptor expression levels and a 16% (P < 0.05) increase in time to peak shortening. Furthermore, cardiac myocytes isolated from castrated animals also displayed an 18% (P < 0.001) increase in time to relengthening and an 80% decrease in Na/Ca exchanger gene expression when compared with intact controls. Testosterone treatment of castrated animals completely reversed these effects. These results provide the first evidence that androgens regulate functional expression of the L-type calcium channel and the Na/Ca exchanger in isolated rat ventricular myocytes and thus may play a role in modulating cardiac performance in males and thereby contribute to the observed gender differences in cardiac function.

Animals↗
PubMed2003

Chronic high pressure potentiates the antiproliferative effect and abolishes contractile phenotypic changes caused by endothelial cells in cocultured smooth muscle cells.

UNLABELLED: High in vitro pressures have been reported to alter smooth muscle cell (SMC) and endothelial cell (EC) phenotype, while endothelial cells (ECs) can influence the proliferation, phenotype, and contractile features of smooth muscle cells (SMC) in coculture systems. However, little is known about the in vitro effects of pressure on EC/SMC cocultures. We therefore sought to compare SMC proliferation in independent and EC coculture under ambient and high pressure, and identify changes in the contractile phenotype of SMCs by measuring levels of the L-type Ca(2+) channel a(1) subunit (dihydropyridine-DHP receptor) which is critical for Ca(2+) transients, differentiation and contractility in SMC. METHODS: Rat aortic SMCs in independent culture (SMC/0) and coculture with ECs (SMC/EC) were maintained in 5% CO(2) under either atmospheric or high pressure (130 mmHg). SMC were counted at 0, 1, 3, and 5 days and compared to initial cell counts of day 0 before the exposure to experimental conditions. DHP receptor levels were quantitated by Western blotting (three similar studies). RESULTS: ECs suppressed SMC proliferation on day 1 of coculture in both atmospheric and high pressure (20% inhibition vs independent culture, P < or = 0.05). By day 3, cocultured SMC under atmospheric pressure displayed no EC-mediated inhibition, and at day 5, atmospheric cocultured SMCs revealed statistically significant enhanced proliferation as compared with SMCs in independent cultures. However, cocultured SMCs exposed to 130 mmHg pressure displayed sustained sensitivity to EC growth inhibition at both days 3 and 5 of the experiment. Coculture decreased SMC DHP-receptor levels under atmospheric pressure. However, this effect was abolished in cocultures exposed to high pressure. CONCLUSIONS: High pressure substantially alters the regulatory influence of EC on SMC proliferation and contractile potential. This pressure/coculture model should increase our understanding of cellular interaction in hypertensive vasculopathy.

Animals↗
PubMed2003

Decoy calcium channel beta subunits modulate contractile function in myocytes.

To test the hypothesis that mutated beta2-subunits of the L-type calcium channel could serve as a decoy and interdict calcium channel trafficking and function, we engineered a beta2 subunit that contained the beta interaction domain for alpha1c subunit interaction, but lacked N- and C-terminal domains that might be essential for sarcolemmal localization. An adenoviral vector was constructed containing the gene for the beta-interaction domain (BID) fused to green fluorescence protein (GFP), using a vector containing only GFP as control. Freshly plated, dissociated adult rat myocytes were infected and expression and function were assessed at 60 h. Fluorescence microscopy confirmed GFP expression; immunoblot analysis confirmed dose-dependent GFP-BID expression. Mechanical properties of adult rat ventricular myocytes were evaluated using a video edge-detection system. Contractility analysis (optical/video, field stimulation) demonstrated that contracting cells decreased from 60 to 2%. Contractile amplitude (percent shortening) decreases significantly from 5.6 vs. 2.4% with no change in time to peak twitch. Recombinant adenovirus overexpressing mutated beta2 subunits in adult mammalian myocytes can markedly alter excitation-contraction coupling. This paradigm may offer new approaches to understanding and modulating EC coupling.

Adenoviridae↗
PubMed2002

Early use of glycoprotein IIb/IIIa-receptor inhibitors in non-ST-segment-elevation acute coronary syndromes.

The early use of glycoprotein (GP) IIb/IIIa-receptor inhibitors in patients with non-ST-segment-elevation (NSTE) acute coronary syndromes (ACSs) is discussed. Unstable angina and NSTE myocardial infarction, collectively known as NSTE ACSs, are among the leading causes of morbidity and mortality in the United States. Updated guidelines from the American College of Cardiology and the American Heart Association for the management of NSTE ACSs strongly recommend that patients with intermediate- to high-risk features (e.g., ST-segment depression, elevated cardiac markers, and recurrent ischemia) be managed with an early invasive or other aggressive strategy (diagnostic angiography within 48 hours and, if warranted, percutaneous or surgical revascularization) and immediate treatment with a GP IIb/IIIa-receptor inhibitor. In low-risk patients, either an early invasive or an early conservative strategy (diagnostic angiography only for recurrent or refractory ischemia or a positive stress test result) is appropriate. For patients managed with an early conservative approach, the guidelines recommend GP IIb/IIIa-receptor inhibitor therapy with eptifibatide or tirofiban hydrochloride, especially in high-risk patients. Abciximab should not be used in patients in whom percutaneous coronary intervention is not planned. Greater implementation of the recommendations concerning the early use of GP IIb/IIIa-receptor inhibitors may result in reduced mortality rates. A large body of clinical evidence supports the updated ACC and AHA recommendations for managing patients with NSTE ACSs.

Abciximab↗
PubMed2002

A 27 bp cis-acting sequence is essential for L-type calcium channel alpha(1C) subunit expression in vascular smooth muscle cells.

Expression of L-type calcium channels in cardiac myocytes and vascular smooth muscle cells (VSMC) critically regulates the contractile state of these cells. In order to discover the elements in the promoter region of the Ca(v)1.2 gene encoding the vascular/cardiac calcium channel alpha(1C) subunit that are important for the basal gene expression, approximately 2 kb of the 5'-flanking sequence of the Ca(v)1.2 gene has been cloned in our lab. In this study, using various lengths of the 5'-flanking DNA fused with a luciferase gene as a reporter, we have defined a 493-bp fragment of the cis-regulatory DNA which carries the majority of promoter activity in pulmonary artery smooth muscle (PAC1) cells. DNase I footprinting analysis of this 493-bp DNA using nuclear extracts from PAC1 cells revealed a 27-bp DNA sequence that contains a c-Ets like motif (CAGGATGC). Mutation of the Ets-like site and the respective flanking sequence within the DNase I footprinting protection region induced a marked change in the promoter activity in PAC1 cells. Electrophoretic mobility shift assays (EMSA) confirmed the presence of specific binding factor(s) in PAC1 cells' nuclear extracts for this 27-bp DNA. Competition studies with the wild-type and mutated DNA fragments established the importance of the 27 bp DNA sequence for high-affinity binding of the nuclear proteins to the promoter. We conclude that there is a 27 bp region in the promoter of the Ca(v)1.2 gene to which nuclear proteins from VSMC bind and strongly regulate the basal promoter activity.

Animals↗
PubMed2002

Norepinephrine regulates the in vivo expression of the L-type calcium channel.

The alpha1c subunit (DHP receptor) of the L-type Ca2+ channel is important for calcium homeostasis in cardiac muscle. The DHPr provides the primary mechanism for calcium influx during contraction. Published results demonstrate three in vitro signaling pathways that are important in the regulation of DHPr gene expression in neonatal cardiac myocytes, the protein kinase A (PKA), protein kinase C (PKC) pathways, and intracellular calcium. To determine whether these pathways are important in vivo, we treated adult rats with infusions of isoproterenol, or norepinephrine at 200 microg/kg/h and assessed DHPr mRNA and protein levels. Following a 3-day infusion isoproterenol (ISO) and norepinephrine (NE) produced a small but insignificant reduction in DHPr mRNA levels. When the infusions were continued for 7 days isoproterenol increased DHPr mRNA accumulation to control levels while NE stimulated a 35% increase in DHPr mRNA levels and a 35% increase in protein abundance when compared to controls (p < 0.05). Furthermore, contractility and Ca2+ transient measurements of isolated cardiac myocytes from NE infused animals also display shortened duration of contraction/relaxation and increased intracellular free Ca2+ (DFFI) in response to electrical stimulation (p < 0.01). We conclude norepinephrine treatment alters DHPr mRNA and protein levels, and augments excitation-contraction coupling, and thus may be important for modulating cardiac calcium homeostasis in vivo.

Animals↗
PubMed2002

Altered Ca2+ homeostasis and impaired mitochondrial function in cardiomyopathy.

Altered Ca2+ homeostasis and myocyte death is a major characteristic of the hereditary cardiomyopathy in the dystrophic hamster. Despite numerous studies, the mechanisms that link calcium dysregulation and cell death in this animal model remain unclear. We have shown previously that the maintenance of mitochondrial Ca2+ homeostasis is essential for cell survival, and that loss of mitochondrial Ca2+ is closely correlated with cell death in cultured cells. Here, we have further investigated the role of mitochondrial Na+-Ca2+ exchange (NCE) in the development of cardiomyopathy in the dystrophic hamster. We found that the myocyte death was associated with elevated NCE activity together with a reduced level of matrix Ca2+, and impaired mitochondrial energetics. The upregulation of NCE activity in myopathic heart was also accompanied by enhanced expression of the sarcolemmal Na+-Ca2+ exchange (NCX) without alterations in the L-type Ca2+ channel expression. Treatment of dystrophic hamsters with diltiazem (a potent inhibitor of NCE and Ca2+ channels) prevented the occurrence of cell death and restored the normal expression of NCX. Our findings implicate the dysregulation of both sarcolemmal and mitochondrial Na+-Ca2+ exchange in cell death in the myopathic heart.

Animals↗
PubMed2002

Castration reduces mRNA levels for calcium regulatory proteins in rat heart.

Sex-related differences in the cardiac phenotype have been well established. This study was designed to determine whether androgens regulate myocardial gene expression and play a role in the sex-related differences in the myocardial phenotype. Gonadectomized male rats were treated with testosterone, and myocardial gene expression was examined in whole heart using quantitative real-time PCR. Gonadectomy produced a substantial decrease in mRNA levels for the androgen receptor, Na(+)/Ca(2+) exchanger, L- type calcium channel, and beta(1)-adrenergic receptor (beta(1)AR). Supplementation of testosterone in castrates produced a fivefold increase in androgen receptor mRNA levels. Testosterone treatment of castrates produced almost a sixfold increase in Na(+)/Ca(2+) exchanger mRNA, a tenfold increase in Ltype calcium channel mRNA accumulation, and a fourfold increase in beta(1)AR mRNA levels. Increased calcium channel expression, beta(1)AR expression, and Na(+)/Ca(2+) exchanger expression together may alter cytosolic calcium. These results provide the first evidence that testosterone regulates expression of myocardial calcium regulating genes and thus may play a role in modulating the cardiac phenotype in males.

Animals↗