ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Confocal microscopy of fluo-4 fluorescence in pressurized rat mesenteric small arteries subjected to low-frequency electrical field stimulation revealed Ca2+transients in perivascular nerves and novel, spatially localized Ca2+transients in adjacent smooth muscle cells. These muscle Ca2+transients occur with a very brief latency to the stimulus pulse (most <3 ms). They are wider (≈5 &mgr;m) and last longer (t1/2, 145 ms) than Ca2+sparks. They are abolished by the purinergic receptor (P2X) antagonist suramin, but they are totally unaffected by the &agr;1-adrenoceptor antagonist prazosin or by capsaicin (which inhibits the function of perivascular sensory nerves). We conclude that these novel Ca2+transients represent Ca2+entering smooth muscle cells through P2X receptors activated by ATP released from sympathetic nerves, and we therefore call them “junctional Ca2+transients” or jCaTs. As expected from spontaneous neurotransmitter release, jCaTs also occur spontaneously, with characteristics identical to evoked jCaTs. Visualization of sympathetic neurotransmission shows that purinergic components dominate at low frequencies of sympathetic nerve fiber activation.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—The heart is the first organ to form during embryogenesis and its circulatory function is critical from early on for the viability of the mammalian embryo. Developmental abnormalities of the heart have also been widely recognized as the underlying cause of many congenital heart malformations. Hence, the developmental mechanisms that orchestrate the formation and morphogenesis of this organ have received much attention among classical and molecular embryologists. Due to the evolutionary conservation of many of these processes, major insights have been gained from the studies of a number of vertebrate and invertebrate models, including mouse, chick, amphibians, zebrafish, andDrosophila. In all of these systems, the heart precursors are generated within bilateral fields in the lateral mesoderm and then converge toward the midline to form a beating linear heart tube. The specification of heart precursors is a result of multiple tissue and cell-cell interactions that involve temporally and spatially integrated programs of inductive signaling events. In the present review, we focus on the molecular and developmental functions of signaling processes during early cardiogenesis that have been defined in both vertebrate and invertebrate models. We discuss the current knowledge on the mechanisms through which signals induce the expression of cardiogenic transcription factors and the relationships between signaling pathways and transcriptional regulators that cooperate to control cardiac induction and the formation of a linear heart tube.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Higher doses of inhaled NO exert effects beyond the pulmonary circulation. How such extrapulmonary effects can be reconciled with the presumed short half-life of NO in the blood is unclear. Whereas erythrocytes have been suggested to participate in NO transport, the exact role of plasma in NO delivery in humans is not clear. Therefore, we investigated potential routes of NO decomposition and transport in human plasma. NO consumption in plasma was accompanied by a concentration-dependent increase in nitrite andS-nitrosothiols (RSNOs), with no apparent saturation limit up to 200 &mgr;mol/L. The presence of red blood cells reduced the formation of plasma RSNOs. Intravenous infusion of 30 &mgr;mol/min NO in healthy volunteers increased plasma levels of RSNOs and induced systemic hemodynamic effects at the level of both conduit and resistance vessels, as reflected by dilator responses in the brachial artery and forearm microvasculature. Intravenous application ofS-nitrosoglutathione, a potential carrier of bioactive NO, mimicked the vascular effects of NO, whereas nitrite and nitrate were inactive. Changes in plasma nitrosothiols were correlated with vasodilator effects after intravenous application ofS-nitrosoglutathione and NO. These findings demonstrate that in humans the pharmacological delivery of NO solutions results in the transport and delivery of NO as RSNOs along the vascular tree.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Functional closure of the human ductus arteriosus (DA) is initiated within minutes of birth by O2constriction. It occurs by an incompletely understood mechanism that is intrinsic to the DA smooth muscle cell (DASMC). We hypothesized that O2alters the function of an O2sensor (the mitochondrial electron transport chain, ETC) thereby increasing production of a diffusible redox-mediator (H2O2), thus triggering an effector mechanism (inhibition of DASMC voltage-gated K+channels, Kv). O2constriction was evaluated in 26 human DAs (12 female, aged 9±2 days) studied in their normal hypoxic state or after normoxic tissue culture. In fresh, hypoxic DAs, 4-aminopyridine (4-AP), a Kv inhibitor, and O2cause similar constriction and K+current inhibition (IK). Tissue culture for 72 hours, particularly in normoxia, causes ionic remodeling, characterized by decreased O2and 4-AP constriction in DA rings and reduced O2- and 4-AP–sensitiveIKin DASMCs. Remodeled DAMSCs are depolarized and express less O2-sensitive channels (including Kv2.1, Kv1.5, Kv9.3, Kv4.3, and BKCa). Kv2.1 adenoviral gene-transfer significantly reverses ionic remodeling, partially restoring both the electrophysiological and tone responses to 4-AP and O2. In fresh DASMCs, ETC inhibitors (rotenone and antimycin) mimic hypoxia, increasingIKand reversing constriction to O2, but not phenylephrine. O2increases, whereas hypoxia and ETC inhibitors decrease H2O2production by altering mitochondrial membrane potential (&Dgr;&PSgr;m). H2O2, like O2, inhibitsIKand depolarizes DASMCs. We conclude that O2controls human DA tone by modulating the function of the mitochondrial ETC thereby varying &Dgr;&PSgr;m and the production of H2O2, which regulates DASMC Kv channel activity and DA tone.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Studies were designed to determine the source of NO responsible for buffering of the angiotensin II (Ang II)–mediated decrease of blood flow in the renal medulla. Intracellular Ca2+concentration ([Ca2+]i) and NO production ([NO]i) of pericytes and endothelium of the vasa recta were independently measured with the use of fura 2-AM and 4,5-diaminofluorescein diacetate (DAF-2DA), respectively, in microtissue strips of the vascular bundles of the outer medullary vasa recta. Disruption of the endothelium of the vasa recta by perfusion with latex microspheres enabled imaging of the pericytes. Ang II (1 &mgr;mol/L) produced an increase of [NO]iof 19±6 U in pericytes of the vasa recta when the vessels were adjacent to medullary thick ascending limbs (mTALs). Pericytes of isolated vasa recta without surrounding mTALs showed a rapid peak increase in [Ca2+]iof 248±107 nmol/L, with a sustained elevation of 107±75 nmol/L, but did not show an increase in [NO]ito either Ang II (1 &mgr;mol/L) or the Ca2+ionophore 4-bromo-A23187 (5 &mgr;mol/L). These observations indicated the lack of Ang II and Ca2+-sensitive NO production in pericytes of the vasa recta. In isolated vasa recta with intact endothelium, Ang II reduced [Ca2+]ifrom 128±28 to 62±13 nmol/L and failed to increase [NO]i. However, the Ca2+ionophore did increase [NO]iin the endothelium (47±8 U), indicating the presence of Ca2+-sensitive NO production. Significant increases of [NO]iwere observed in single isolated mTALs in response to both Ang II (33±6 U) and the Ca2+ionophore (51±18 U). We conclude that Ang II increases [Ca2+]iin pericytes of the descending vasa recta as part of its constrictor action and that this vasoconstriction is buffered by the NO from the surrounding tubular elements, such as mTALs.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Apoptosis of neointimal smooth muscle cells is a well-recognized component of the pathogenesis of vascular lesions. In recent studies, we have identified the neurotrophin receptor, p75NTR, as a mediator of apoptosis of neointimal smooth muscle cells. Neurotrophin ligands and p75NTRare selectively expressed in areas of atherosclerotic lesions with increased smooth muscle cell apoptosis and the neurotrophins are potent apoptotic agents for p75NTR-expressing smooth muscle cells in vitro. In the present study, we directly assess the role of p75NTRin lesion development in the flow-restricted carotid artery, a model of murine vascular injury. Ligation of the left carotid artery resulted in a 3- to 4-fold increase in lesion development in p75NTR-null mutant mice as compared with wild-type mice. The increase in lesion size was associated with a 70% decrease in apoptosis of neointimal smooth muscle cells, as assessed by in situ TUNEL analysis. These data suggest that under conditions of flow restriction, p75NTRactivation impairs lesion formation by promoting smooth muscle cell apoptosis. These results further implicate p75NTRas an important regulator of smooth muscle cell apoptosis and lesion development after vascular injury.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Cell replacement therapy is a promising approach for the treatment of cardiac diseases, but is challenged by a limited supply of appropriate cells. We have investigated whether functional cardiomyocytes can be efficiently generated from human embryonic stem (hES) cells. Cardiomyocyte differentiation was evaluated using 3 parent (H1, H7, and H9) hES cell lines and 2 clonal (H9.1 and H9.2) hES cell lines. All cell lines examined differentiated into cardiomyocytes, even after long-term culture (50 passages or ≈260 population doublings). Upon differentiation, beating cells were observed after one week in differentiation conditions, increased in numbers with time, and could retain contractility for over 70 days. The beating cells expressed markers characteristic of cardiomyocytes, such as cardiac &agr;-myosin heavy chain, cardiac troponin I and T, atrial natriuretic factor, and cardiac transcription factors GATA-4, Nkx2.5, and MEF-2. In addition, cardiomyocyte differentiation could be enhanced by treatment of cells with 5-aza-2′-deoxycytidine but not DMSO or retinoic acid. Furthermore, the differentiated cultures could be dissociated and enriched by Percoll density centrifugation to give a population containing 70% cardiomyocytes. The enriched population was proliferative and showed appropriate expression of cardiomyocyte markers. The extended replicative capacity of hES cells and the ability to differentiate and enrich for functional human cardiomyocytes warrant further development of these cells for clinical application in heart diseases.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Phosphorylation of myofilament proteins by kinases such as cAMP-dependent protein kinase and protein kinase C has been shown to lead to altered thin-filament protein-protein interactions and modulation of cardiac function in vitro. In the present study, we report that a small GTPase-dependent kinase, p21-activated kinase (PAK), increases the calcium sensitivity of Triton-skinned cardiac muscle fiber bundles. Constitutively active PAK3 caused an average 1.25-fold (25.0±6.0%, n=6) increase in force at pCa 5.75, 1.44-fold (44.0±7.78%, n=6) at pCa 6.25, and 2.41-fold (141.2±23.7%, n=4) at pCa 6.5, representing a change in pCa50value of approximately 0.25. Constitutively active PAK3 produced no change in force under conditions of relaxation (pCa 8.0) or maximal contraction (pCa 4.5). Furthermore, an inactive, kinase-dead form of PAK3 failed to produce any change in force development at any pCa value. The myofilament proteins phosphorylated by PAK3, at pCa 6.5, are desmin, troponin T, troponin I, and an unidentified 70-kDa protein. Importantly, cardiac troponin I was found to be phosphorylated at serine 149 of human cardiac troponin I, representing a novel phosphorylation site. These findings suggest a novel mechanism of modulating the calcium sensitivity of cardiac muscle contraction.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID