ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The delineation of the mechanisms that regulate cardiac gene expression is central to our understanding of cardiac growth and development. Much progress has been made toward the identification of factors involved in tissue-restricted gene expression, especially in skeletal muscle cells. However, the mechanisms regulating the expression of cardiac-specific genes remain less well understood. Certain homeodomain proteins have been implicated in commitment to the cardiac phenotype. Among the best characterized are the murine proteins Csx, Nkx-2.5, and Nkx-2.6, related to the protein tinman, which is essential for heart formation in Drosophila. The expression of these genes precedes that of cardiac-specific genes and is therefore believed to play a critical role in the development of the heart. The GATA proteins are a family of zinc finger proteins that are also expressed early in cardiac development and may act separately from, or in concert with, the homeodomain proteins as crucial regulators of heart development. The myosin heavy and light chain genes, the actin genes, the troponin genes, and the atrial natriuretic factor and muscle creatine kinase genes have served as excellent paradigms for the study of cardiac gene expression. Although differences in cis-acting elements and their behavior in binding assays have been observed between different genes, there exist similarities that are noteworthy. In this review, we will discuss the factors involved in the regulation of cardiac-specific gene expression in an attempt to provide a better understanding of the process of cardiogenesis.(Circ Res. 1996;79:4-13.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The expression of L- and T-type Ca2plus channels has been reported to change during various biological events, including cellular differentiation and proliferation. The present study aimed to examine whether or not the expression of L- and T-type Ca2plus channels depends on the cell cycle in rat aortic smooth muscle cells in primary culture. Both the phase of the cell cycle and the functional expression of Ca2plus channels were determined in the same single cell, using an immunocytochemical analysis of cell cycle-specific nuclear antigens and a whole-cell voltageclamp method, respectively. In the G0(n equals 130) and M (n equals 75) phases, all cells showed only L-type Ca2plus currents. The cells showing a T-type Ca2plus current appeared in the G1phase (37%, n equals 85) and increased in the S phase (90%, n equals 21). For L-type Ca2plus channels, the current density was significantly greater in the G1phase than in the G0and M phases. However, either the voltage-dependent properties or the dose-response relationships of Bay K 8644- and second messenger-induced modulations of L-type Ca2plus current did not differ in the four phases of the cell cycle. These findings thus indicate that the expression of L- and T-type Ca2plus channels depends on the cell cycle, whereas the characteristics of L-type Ca2plus channels do not differ between the phases of the cell cycle.(Circ Res. 1996;79:14-19.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The effect of arachidonic acid (AA) on the delayed rectifier K sup plus current (I sub K) was evaluated in rat pulmonary myocytes by using the whole-cell patch-clamp technique. Externally applied AA (50 micro mol/L) caused a membrane depolarization, averaging 16 mV in six cells. AA (1 to 50 micro mol/L) caused a dual effect on I sub K. First, AA accelerated the rate of IKactivation, increasing current amplitude at the beginning of voltage step. Second, AA caused a marked acceleration of current decay, thereby reducing IKamplitude measured toward the end of the depolarizing steps. These effects were not prevented by indomethacin or nordihydroguaiaretic acid, blockers of cyclooxygenase and lipoxygenase, respectively. AA did not affect the voltage dependence of current activation or inactivation. The magnitude of the inhibitory effect on IKwas correlated with the number of double bonds but was independent of tail length in fatty acids containing between 14 and 22 carbons. Linoleic acid (18:2, cis-9,12) inhibited IKmuch more than did its trans-stereoisomer, linolelaidic acid. Arachidonyl alcohol, which is uncharged, and arachidonyl coenzyme A, which does not `flip' across the cell membrane, were less effective than AA in inhibiting IK; this effect of fatty acids may therefore require passage across the cell membrane. The enhancement of early IKwas mimicked by the protein kinase C (PKC) stimulator 1-oleoyl-2-acetyl-sn-glycerol (10 micro mol/L), was suppressed by ATP removal from the pipette solution, and was blocked by PKC inhibitors chelerythrine (10 micro mol/L) and staurosporine (100 nmol/L). This effect may therefore require PKC-dependent phosphorylation.(Circ Res. 1996;79:20-31.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

A major determinant of the level of cellular superoxide anion (O sub 2 sup minus small bullet) is the dismutation of O sub 2 sup minus small bullet to hydrogen peroxide by the enzyme superoxide dismutase (SOD). Three forms of SOD exist, but in endothelial cells, the major form outside of the mitochondria is the cytosolic copper/zinc-containing superoxide dismutase (Cu/Zn SOD). Since fluid shear stress is an important determinant of the function and structure of endothelial cells in vivo, we examined the effect of laminar shear stress on the expression of Cu/Zn SOD in cultured human aortic endothelial cells. Laminar shear stress of 0.6 to 15 dyne/cm sup 2 increased Cu/Zn SOD mRNA in a time- and dose-dependent manner in human aortic endothelial cells. Shear stress also increased both Cu/Zn SOD protein content and the enzyme activity. Nuclear run-on assays showed that nuclei from human aortic endothelial cells exposed to laminar shear stress had a 1.6-fold greater transcriptional activity of the Cu/Zn SOD gene compared with cells not exposed to shear, indicating that an increase in Cu/Zn SOD mRNA induced by laminar shear stress is at least in part mediated by increased transcription. In contrast, shear stress had no effect on Cu/Zn SOD mRNA levels in human aortic smooth muscle cells. These findings show that physiological levels of shear stress increase expression of Cu/Zn SOD in the endothelium. This adaptation to shear stress might augment the effect of locally produced NObulletand thereby promote the antiatherogenic and anti-inflammatory properties of the endothelial cell.(Circ Res. 1996;79:32-37.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

NO generated by endothelial cells is vasoprotective by antagonizing platelet adhesion and smooth muscle contraction. Since vascular smooth muscle cells (VSMCs) produce NO in response to cytokine stimulation and after arterial injury, we speculated that NO produced by VSMCs could compensate for the loss of endothelium. Using balloon catheter denudation of the rat carotid artery as a model for arterial injury and restenosis, we have evaluated the time course of expression of inducible NO synthase (iNOS) by in situ hybridization and immunohistochemistry and studied the effect of iNOS on platelet adhesion and blood flow of the injured vessel. iNOS mRNA and protein were expressed in the innermost layer of the media from day 1 and were subsequently detected in the neointima, whereas no expression was detectable in the uninjured artery. Systemic administration of Nomega-nitro-L-arginine methyl ester (L-NAME) resulted in a twofold to threefold increase in the adhesion of111In-labeled platelets to the injured vessel wall. Platelet adhesion was also enhanced threefold by local delivery of L-NAME from a gel surrounding the injured vessel, whereas the stereoisomer, D-NAME, had no effect. Finally, inhibition of NO synthase led to a 24% reduction of the blood flow in the injured carotid artery. These results demonstrate that arterial injury triggers the expression of iNOS in the lesion and that NO produced by iNOS inhibits platelet adhesion and restores blood flow. This could explain the disappearance of platelet thrombi from deendothelialized arterial surfaces within a few days after injury and indicates the importance of NO generated by iNOS for the maintenance of vascular tone. Thus, expression of iNOS in lesions may represent a protective mechanism that compensates for the loss of endothelium.(Circ Res. 1996;79:38-44.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Abrupt reductions in fluid shear stress induce subendothelial smooth muscle cells (SMCs) to proliferate in experimental prosthetic grafts. Platelet-derived growth factor (PDGF), an important SMC mitogen, is expressed by cultured endothelial cells and modulated by shear stress. We hypothesized that this growth factor would be modulated by changes in shear stress in vivo. Bilateral aortoiliac prosthetic grafts were implanted into five baboons. High flow was generated by construction of femoral arteriovenous fistulas on both sides. Two months later, one of the fistulas was ligated, reducing shear stress in the upstream graft by 78 plus minus 6%. Four days after fistula ligation, all grafts were removed and analyzed. As previously reported, SMC proliferation in low-flow grafts exceeded that in high-flow grafts, although the neointimal area was similar. mRNA levels for PDGF-A were significantly increased in low-flow grafts compared with high-flow grafts. In situ hybridization and immunohistochemical studies localized the increased PDGF-A mRNA and protein to the luminal endothelium and subjacent SMCs. Abrupt reductions in blood flow and fluid shear stress may induce accelerated neointimal thickening by a PDGF-A-mediated mechanism, since endothelial expression of this gene is temporally and anatomically associated with neointimal SMC proliferation.(Circ Res. 1996;79:45-53.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The vascular response to changes in oxygen levels in the blood and tissue is a highly adaptive physiological response that functions to match tissue oxygen supply to metabolic demand. Defining the cellular mechanisms that can sense physiologically relevant changes in PO2and adjust vascular diameter are vital to our understanding of this process. A cytochrome P450 (P450) enzyme of the 4A family of omega-hydroxylases was localized in renal microvessels, renal cortex, and a striated muscle microvascular bed (cremaster) of the rat. In the presence of molecular oxygen, this P450 enzyme catalyzes formation of 20-HETE from arachidonic acid (AA). Prior studies have shown that 20-HETE potently contracts renal and cerebral arteries and arterioles. The present study demonstrates that 20-HETE constricts striated muscle arterioles as well. In both intact renal microvessels and enriched renal cortical microsomal enzyme preparations, the formation of 20-HETE was linearly dependent on PO2between 20 and 140 mm Hg. Homogenates of cremaster tissue produced 20-oxygen HETE when incubated with AA. They also expressed message for P450 4A enzyme, as determined by Southern and Western blots. Administration of 17-octadecynoic acid (17-ODYA), which is a P450 4A inhibitor, attenuated the constriction of third-order cremasteric arterioles in response to elevation of superfusion solution PO2from approximate equals 3 to 5 mm Hg to approximate equals 35 mm Hg. 17-ODYA had no effect on basal vascular tone or response of cremaster arterioles to vasoactive compounds. These results demonstrate the existence of P450 omega-hydroxylase activity and 20-HETE formation in the vasculature and parenchyma of at least two microvascular beds. Our data suggest that a P450 enzyme of the 4A family has the potential to function as an oxygen sensor in mammalian microcirculatory beds and to regulate arteriolar caliber by generating 20-HETE in an oxygen-dependent manner.(Circ Res. 1996;79:54-61.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The potential for exogenous infusion of basic fibroblast growth factor (bFGF) to increase collateral blood flow to dependent tissue was quantified in adult male rats with peripheral arterial insufficiency. Occlusion of the femoral artery at a proximal site did not infringe on resting blood flow to the distal hindlimb muscle, but did remove the blood flow reserve. Blood flow to the hindlimb muscles was measured with radiolabeled microspheres using an isolated hindlimb preparation perfused in the descending aorta (Krebs-Henseleit bicarbonate, 5% albumin medium containing red blood cells [40% hematocrit]) at 100 mm Hg. Calf muscle blood flow changed modestly (approximate equals 50%) with infusion of only the carrier (heparin/saline), increased markedly over the first 2 weeks of bFGF infusion (1 micro gram/d into the femoral artery), but did not change further with infusion for 4 weeks. Waiting 2 weeks after 1 week of bFGF infusion did not further increase the intermediate improvement in blood flow. The improved collateral blood flow and increased muscle capillary density likely contributed to the enhanced muscle performance observed during nerve stimulation in situ. X-ray films of arterial casts identified an expansion of upper thigh vessels that likely served as collaterals. In animals with peripheral arterial insufficiency, short-term exogenous infusion of bFGF is effective at inducing vascular expansion that is sufficient to improve the flow reserve of dependent distal tissue and enhance muscle function. This raises the expectation that a similar response in patients with peripheral arterial insufficiency would significantly improve morbidity, including the symptoms of intermittent claudication.(Circ Res. 1996;79:62-69.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Aortic fibronectin (FN) expression is augmented in hypertension. Increasing evidence suggests that both angiotensin II (Ang II) and mechanical factors may induce vascular remodeling in response to hypertension. We have previously shown that, in vitro, increased transmural pressure enhances FN expression in rabbit aortic media. To investigate the existence of a link between the effects of pressure and Ang II and to explore the mechanisms underlying such a relationship, we quantified the effect of Ang II and Ang II inhibitors on the pressure-dependent FN expression in a 3-day organ culture model of rabbit aorta using immunolabeling analysis and detected FN mRNAs by in situ hybridization. A dose-dependent effect of Ang II on FN expression was observed at both 80 and 150 mm Hg but not at 0 mm Hg (relaxed vessels). One micro mol/L Ang II increased the media cross-sectional surface, showing FN expression from 7.9 plus minus 0.7% (n equals 9) to 18.9 plus minus 1.1% (n equals 4) at 80 mm Hg (P less than .01) and from 17.4 plus minus 1.8% (n equals 9) to 56.6% plus minus 3.6 (n equals 4) at 150 mm Hg (P less than .001). In situ hybridization revealed that Ang II and pressure upregulated FN mRNA expression. Losartan, an AT1antagonist, not only blocked the Ang II effect but also inhibited the transmural pressure effect. Angiotensin-converting enzyme inhibition abolished the pressure-dependent FN expression and significantly diminished the effect of pressure in the presence of Ang II. The effect of renin-angiotensin system inhibitors was specific for FN, since neither bFGF nor laminin expression was affected by these agents. Taken together, the results demonstrate that (1) the effect of transmural pressure is mediated by the stimulation of a local renin-angiotensin system, resulting in a net Ang II production in the culture medium, (2) transmural pressure and Ang II act synergistically to enhance vascular FN expression, (3) AT1receptors mediate both the effects of pressure and of exogenous Ang II, and (4) the effect of Ang II on FN expression is regulated at a pretranslational level.(Circ Res. 1996;79:70-78.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID