摘要:

Brugada syndrome is an inherited cardiac disease that causes sudden death related to idiopathic ventricular fibrillation in a structurally normal heart. The disease is characterized by ST-segment elevation in the right precordial ECG leads and is frequently accompanied by an apparent right bundle-branch block. The biophysical properties of theSCN5Amutation T1620M associated with Brugada syndrome were examined for defects in intermediate inactivation (IM), a gating process in Na+channels with kinetic features intermediate between fast and slow inactivation. Cultured mammalian cells expressing T1620M Na+channels in the presence of the human &bgr;1subunit exhibit enhanced intermediate inactivation at both 22°C and 32°C compared with wild-type recombinant human heart Na+channels (WT-hH1). Our findings support the hypothesis that Brugada syndrome is caused, in part, by functionally reduced Na+current in the myocardium due to an increased proportion of Na+channels that enter theIMstate. This phenomenon may contribute significantly to arrhythmogenesis in patients with Brugada syndrome. The full text of this article is available at http://www.circresaha.org.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Cardiomyopathy (CM) comprises a heterogeneous group of diseases, including ischemic (ICM) and dilative (DCM) forms. The pathogenesis of primary DCM is not clearly understood. Recent studies in mice show that vascular endothelial growth factor (VEGF) is involved in ICM. Whether VEGF plays a role in human CM is unknown. We examined the mRNA and protein expression of VEGF and its receptors in hearts of patients with end-stage DCM and ICM and in healthy individuals using real-time polymerase chain reaction and Western blotting. Number of capillaries, area of myocytes, and collagen were calculated in cardiac biopsies using transmission electron microscopy. In DCM, except for VEGF-C, mRNA transcript levels of VEGF-A165, VEGF-A189, and VEGF-B and the protein level of VEGF-A and VEGF-R1were downregulated compared with controls (P<0.05). However, in ICM, mRNA transcript levels of VEGF isoforms and protein levels of VEGF-C were upregulated. The vascular density was decreased in DCM but increased in ICM compared with controls (P<0.05). Muscular hypertrophy was not different for ICM and DCM, although DCM had more collagen (P<0.05). Blunted VEGF-A and VEGF-R1protein expression and downregulated mRNA of the predominant isoform of VEGF-A, VEGF-A165, to our knowledge shown here for the first time, provide evidence that the VEGF-A defect in DCM is located upstream. Whether downregulation of certain VEGF isoforms in DCM is a cause or consequence of this disorder remains unclear, although upregulated VEGF levels in ICM are most likely the result of ischemia.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Loss of membrane permeability caused by ischemia leads to cellular sodium accumulation and myocardial edema. This phenomenon has important implications to left ventricular structure and function in the first hours after myocardial infarction. We hypothesized that during this period of time, after prolonged coronary occlusion and complete reflow, the rate of myocardial sodium accumulation is governed by microvascular integrity. We used 3-dimensional23Na MRI to monitor myocardial sodium content changes over time in an in vivo closed-chest canine model (n=13) of myocardial infarction and reperfusion. Infarcts with microvascular obstruction (MO) defined by both radioactive microspheres and contrast-enhanced1H MRI showed a slower rate of sodium accumulation as well as lower blood flow at 20 minutes and 6 hours after reperfusion. Conversely, the absence of MO was associated with faster rates of sodium accumulation and greater blood flow restoration. In addition, infarct size by23Na MRI correlated best with infarct size by triphenyltetrazolium chloride and contrast-enhanced1H MRI at 9 hours after reperfusion. We conclude that in reperfused myocardial infarction, sodium accumulation is dependent on microvascular integrity and is slower in regions of MO compared with those with patent microvasculature. Finally,23Na MRI can be a useful tool for monitoring in vivo myocardial sodium content in acute myocardial infarction.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Electrical uncoupling at gap junctions during acute myocardial ischemia contributes to conduction abnormalities and reentrant arrhythmias. Increased levels of intracellular Ca2+and H+and accumulation of amphipathic lipid metabolites during ischemia promote uncoupling, but other mechanisms may play a role. We tested the hypothesis that uncoupling induced by acute ischemia is associated with changes in phosphorylation of the major cardiac gap junction protein, connexin43 (Cx43). Adult rat hearts perfused on a Langendorff apparatus were subjected to ischemia or ischemia/reperfusion. Changes in coupling were monitored by measuring whole-tissue resistance. Changes in the amount and distribution of phosphorylated and nonphosphorylated isoforms of Cx43 were measured by immunoblotting and confocal immunofluorescence microscopy using isoform-specific antibodies. In control hearts, virtually all Cx43 identified immunohistochemically at apparent intercellular junctions was phosphorylated. During ischemia, however, Cx43 underwent progressive dephosphorylation with a time course similar to that of electrical uncoupling. The total amount of Cx43 did not change, but progressive reduction in total Cx43 immunofluorescent signal and concomitant accumulation of nonphosphorylated Cx43 signal occurred at sites of intercellular junctions. Functional recovery during reperfusion was associated with increased levels of phosphorylated Cx43. These observations suggest that uncoupling induced by ischemia is associated with dephosphorylation of Cx43, accumulation of nonphosphorylated Cx43 within gap junctions, and translocation of Cx43 from gap junctions into intracellular pools.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Because the amount and structure of type I collagen are thought to affect the mechanics of ventricular myocardium, we investigated myocardial collagen structure and passive mechanical function in the osteogenesis imperfecta murine (oim) model of pro-&agr;2(I) collagen deficiency, previously shown to have less collagen and impaired biomechanics in tendon and bone. Compared with wild-type littermates, homozygousoimhearts exhibited 35% lower collagen area fraction (P<0.05), 38% lower collagen fiber number density (P<0.05), and 42% smaller collagen fiber diameter (P<0.05). Compared with wild-type,oimleft ventricular (LV) collagen concentration was 45% lower (P<0.0001) and nonreducible pyridinoline cross-link concentration was 22% higher (P<0.03). Mean LV volume during passive inflation from 0 to 30 mm Hg in isolated hearts was 1.4-fold larger foroimthan wild-type (P=NS). Uniaxial stress-strain relations in resting right ventricular papillary muscles exhibited 60% greater strains (P<0.01), 90% higher compliance (P=0.05), and 64% higher nonlinearity (P<0.05) inoim. Mean opening angle, after relief of residual stresses in resting LV myocardium, was 121±9 degrees inoimcompared with 45±4 degrees in wild-type (P<0.0001). Mean myofiber angle inoimwas 23±8 degrees greater than wild-type (P<0.02). Decreased myocardial collagen diameter and amount inoimis associated with significantly decreased fiber and chamber stiffness despite modestly increased collagen cross-linking. Altered myofiber angles and residual stress may be beneficial adaptations to these mechanical alterations to maintain uniformity of transmural fiber strain. In addition to supporting and organizing myocytes, myocardial collagen contributes directly to ventricular stiffness at high and low loads and can influence stress-free state and myofiber architecture.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Matrix metalloproteinase (MMP)-2 has been historically associated with the process of vascular remodeling through the cleavage of extracellular matrix proteins. However, we recently found that MMP-2 also cleaves the endothelium-derived peptide big endothelin-1, ET-1[1–38] and yields the novel vasoconstrictor ET-1[1–32]. We therefore investigated the effects of MMP-2 inhibitors as potential vasodilators. MMP inhibition with ortho-phenanthroline (0.3 to 30 &mgr;mol/L) induced vasorelaxation of isolated rat mesenteric arteries (maximum of relaxation=74.5±27.6% at 30 &mgr;mol/L). However, phosphoramidon (0.3 to 30 &mgr;mol/L), which inhibits some metalloenzymes, but not MMP-2, did not dilate the arteries. Selective inhibition of endogenous MMP-2 with the novel tissue-permeable cyclic peptide CTTHWGFTLC (CTT, 10 &mgr;mol/L) also caused vasorelaxation (by 85±6%), whereas STTHWGFTLS (10 &mgr;mol/L), an inactive CTT analogue, did not dilate the arteries. Interestingly, the vasorelaxation that results from MMP-2 inhibition was endothelium-independent. Thus, we examined whether MMP-2 acted on peptides derived from the smooth muscle or the perivascular nerves. Recombinant human MMP-2 cleaved calcitonin gene-related peptide (CGRP) specifically at the Gly14-Leu15peptide bond and reduced the vasodilatory potency of CGRP by 20-fold. Inhibition of MMP-2 increased the amount of intact CGRP in arteries and enhanced vasorelaxation induced by anandamide, which stimulates CGRP release. Vasorelaxation in response to MMP-2 inhibition was abolished by CGRP[8–37], a selective CGRP receptor antagonist, and by capsaicin, which depletes arterial perivascular nerves of CGRP. We conclude that vascular MMP-2 cleaves endogenous CGRP and promotes vasoconstriction. These data suggest a novel mechanism of regulating the vasoactive and, possibly, the neurohormonal actions of CGRP and establish MMP-2 as a modulator of vascular function.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

17&bgr;-Estradiol (E2) is a rapid activator of endothelial nitric oxide synthase (eNOS). The product of this activation event, NO, is a fundamental determinant of cardiovascular homeostasis. We previously demonstrated that E2-stimulated endothelial NO release can occur without an increase in cytosolic Ca2+. Here we demonstrate for the first time, to our knowledge, that E2rapidly induces phosphorylation and activation of eNOS through the phosphatidylinositol 3 (PI3)-kinase–Akt pathway. E2treatment (10 ng/mL) of the human endothelial cell line, EA.hy926, resulted in increased NO production, which was abrogated by the PI3-kinase inhibitor, LY294002, and the estrogen receptor antagonist ICI 182,780. E2stimulated rapid Akt phosphorylation on serine 473. As has been shown for vascular endothelial growth factor, eNOS is an E2-activated Akt substrate, demonstrated by rapid eNOS phosphorylation on serine 1177, a critical residue for eNOS activation and enhanced sensitivity to resting cellular Ca2+levels. Adenoviral-mediated EA.hy926 transduction confirmed functional involvement of Akt, because a kinase-deficient, dominant-negative Akt abolished E2-stimulated NO release. The membrane-impermeant E2BSA conjugate, shown to bind endothelial cell membrane sites, also induced rapid Akt and consequent eNOS phosphorylation. Thus, engagement of membrane estrogen receptors results in rapid endothelial NO release through a PI3-kinase–Akt-dependent pathway. This explains, in part, the reduced requirement for cytosolic Ca2+fluxes and describes an important pathway relevant to cardiovascular pathophysiology.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID