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:

Several time- and voltage-dependent ionic currents have been identified in cardiac pacemaker cells, including Na+current, L- and T-type Ca2+currents, hyperpolarization-activated cation current, and various types of delayed rectifier K+currents. Mathematical models have demonstrated that spontaneous action potentials can be reconstructed by incorporating these currents, but relative contributions of individual currents vary widely between different models. In 1995, the presence of a novel inward current that was activated by depolarization to the potential range of the slow diastolic depolarization in rabbit sinoatrial (SA) node cells was reported. Because the current showed little inactivation during depolarizing pulses, it was called the sustained inward current (Ist). A similar current is also found in SA node cells of the guinea pig and rat and in subsidiary pacemaker atrioventricular node cells. Recently, single-channel analysis has revealed a nicardipine-sensitive, 13-pS Na+current, which is activated by depolarization to the diastolic potential range in guinea pig SA node cells. This channel differs from rapid voltage-gated Na+or L-type Ca2+channels both in unitary conductance and gating kinetics. BecauseIstwas observed only in spontaneously beating SA node cells, ie, it was absent in quiescent cells dissociated from the same SA or atrioventricular node, an important role ofIstfor generation of intrinsic cardiac automaticity was suggested.(Circ Res. 2000;87:88-91.)

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Agonists of G protein–coupled receptors, such as thrombin, act in part by transactivating the epidermal growth factor (EGF) receptor (EGFR). Although at first a ligand-independent mechanism for EGFR transactivation was postulated, it has recently been shown that this transactivation by various G protein–coupled receptor agonists can involve heparin-binding EGF-like growth factor (HB-EGF). Because thrombin stimulation of vascular smooth muscle cell migration is blocked by heparin and because heparin can displace HB-EGF, we investigated the possibility that thrombin stimulation of smooth muscle cells (SMCs) depends on EGFR activation by HB-EGF. In rat SMCs, EGFR phosphorylation and extracellular signal-regulated kinase (ERK) activation in response to thrombin are inhibited not only by the EGFR inhibitor AG1478 and by EGFR blocking antibody but also by heparin and by neutralizing HB-EGF antibody. HB-EGF–dependent signaling induced by thrombin is inhibited by batimastat, which suggests a requirement for pro-HB-EGF shedding by a metalloproteinase. We further demonstrate that this novel pathway is required for the migration of rat and baboon SMCs in response to thrombin. We conclude from these data that the inhibitory effect of heparin on SMC migration induced by thrombin relies, at least in part, on a blockade of HB-EGF–mediated EGFR transactivation.(Circ Res. 2000;87:92-98.)

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Asymmetrical dimethylarginine (ADMA) is an endogenous nitric oxide synthase inhibitor. It is formed by protein arginineN-methyltransferases (PRMTs), which utilizeS-adenosylmethionine as methyl group donor. ADMA plasma concentration is elevated in hypercholesterolemia, leading to endothelial dysfunction and producing proatherogenic changes of endothelial cell function. Four different isoforms of human PRMTs have been identified. Because the release of ADMA from human endothelial cells is increased in the presence of native or oxidized LDL cholesterol, we investigated the potential involvement of PRMT activity and gene expression in this effect. We found that the production of ADMA by human endothelial cells is upregulated in the presence of methionine or homocysteine and inhibited by either of the methyltransferase inhibitorsS-adenosylhomocysteine, adenosine dialdehyde, or cycloleucine. This effect is specific for ADMA but not symmetrical dimethylarginine. The upregulation of ADMA release by native and oxidized LDL is abolished byS-adenosylhomocysteine and by the antioxidant pyrrollidine dithiocarbamate. Furthermore, a methyl-14C label is transferred fromS-adenosylmethionine to ADMA but not symmetrical dimethylarginine, in human endothelial cells. The expression of PRMTs is upregulated in the presence of native or oxidized LDL. Our data suggest that the production of ADMA by human endothelial cells is regulated byS-adenosylmethionine–dependent methyltransferases. This activity is upregulated by LDL cholesterol, which may be due in part to the enhanced gene expression of PRMTs. In concentrations reached by stimulation of methyltransferases (5 to 50 &mgr;mol/L), ADMA significantly inhibited the formation of15N-nitrite from l-[guanidino-15N2]arginine. These findings suggest a novel mechanism by which ADMA concentration is elevated in hypercholesterolemia, leading to endothelial dysfunction and atherosclerosis.(Circ Res. 2000;87:99-105.)

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Coupling between L-type Ca2+channels (dihydropyridine receptors, DHPRs) and ryanodine receptors (RyRs) plays a pivotal role in excitation-contraction (E-C) coupling in cardiac myocytes, and Ca2+influx is generally accepted as the trigger of sarcoplasmic reticulum (SR) Ca2+release. The L-type Ca2+channel agonist BayK 8644 (BayK) has also been reported to alter RyR gating via a functional linkage between DHPR and RyR, independent of Ca2+influx. Here, the effect of rapid BayK application on resting RyR gating in intact ferret ventricular myocytes was measured as Ca2+spark frequency (CaSpF) by confocal microscopy and fluo 3. BayK increased resting CaSpF by 401±15% within 10 seconds in Ca2+-free solution, and depolarization had no additional effect. The effect of BayK on CaSpF was dose-dependent, but even 50 nmol/L BayK induced a rapid 245±12% increase in CaSpF. Nifedipine (5 &mgr;mol/L) had no effect by itself on CaSpF, but it abolished the BayK effect (presumably by competitive inhibition at the DHPR). The nondihydropyridine Ca2+channel agonist FPL-64176 (1 &mgr;mol/L) did not alter CaSpF (despite rapid and potent enhancement of Ca2+current,ICa). In striking contrast to the very rapid and depolarization-independent effect of BayK on CaSpF, BayK increasedICaonly slowly (&tgr;=18 seconds), and the effect was greatly accelerated by depolarization. We conclude that in ferret ventricular myocytes, BayK effects onICaand CaSpF both require drug binding to the DHPR, but postreceptor pathways may diverge in transmission to the gating of the L-type Ca2+channel and RyR.(Circ Res. 2000;87:106-111.)

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

ATP-sensitive K+channels (KATP) contribute to the regulation of tone in vascular smooth muscle cells. We determined the effects of protein kinase C (PKC) activation on the nucleoside diphosphate–activated (KNDP) subtype of vascular smooth muscle KATPchannel. Phorbol 12,13-dibutyrate (PdBu) and angiotensin II inhibited KNDPactivity of C-A patches of rabbit portal vein (PV) myocytes, but an inactive phorbol ester was without effect, and pretreatment with PKC inhibitor prevented the actions of PdBu. Constitutively active PKC inhibited KNDPin I-O patches but was without effect in the presence of a specific peptide inhibitor of PKC. PdBu increased the duration of a long-lived interburst closed state but was without effect on burst duration or intraburst kinetics. PdBu treatment inhibited KNDP, but not a 70-pS KATPchannel of rat PV. The results indicate that the KNDPsubtype of vascular smooth muscle KATPchannel is inhibited by activation of PKC. Control of KNDPactivity by intracellular signaling cascades involving PKC may, therefore, contribute to control of tone and arterial diameter by vasoconstrictors.(Circ Res. 2000;87:112-117.)

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Apoptosis has been implicated in ischemic heart disease, but its mechanism in cardiomyocytes has not been elucidated. In this study, we investigate the effects of hypoxia and reoxygenation in adult cardiomyocytes and the molecular mechanism involved in cardiomyocyte apoptosis. Morphologically, reoxygenation induced rounding up of the cells, appearance of membrane blebs that were filled with marginated mitochondria, and ultrastructural findings characteristic of apoptosis. Reoxygenation (18 hours of reoxygenation after 6 hours of hypoxia) and prolonged hypoxia (24 hours of hypoxia) resulted in a 59% and 51% decrease in cellular viability, respectively. During reoxygenation, cell death occurred predominantly via apoptosis associated with appearance of cytosolic cytochromecand activation of caspase-3 and -9. However, nonapoptotic cell death predominated during prolonged hypoxia. Both caspase inhibition and Bcl-2 overexpression during reoxygenation significantly improved cellular viability through inhibition of apoptosis but had minimal effect on hypoxia-induced cell death. Bcl-2 overexpression blocked reoxygenation-induced cytochromecrelease and activation of caspase -3 and -9, but caspase inhibition alone did not block cytochromecrelease. These results suggest that apoptosis predominates in cardiomyocytes after reoxygenation through a mitochondrion-dependent apoptotic pathway, and Bcl-2 prevents reoxygenation-induced apoptosis by inhibiting cytochromecrelease from the mitochondria and prevents activation of caspase-3 and -9.(Circ Res. 2000;87:118-125.)

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Tissue factor (TF), the initiator of coagulation, is thought to function predominantly at the cell surface. Recent data have suggested that active TF is present extracellularly in atherosclerotic plaques, the arterial wall, and the blood. This study was conducted to determine whether smooth muscle cells (SMCs), a major source of arterial TF, could generate extracellular TF. Active TF accumulated in the medium of cultured human SMCs, representing ≈10% of that measured in the underlying cells at 24 hours. Platelet-derived growth factor, phorbol ester, and tumor necrosis factor-&agr; caused ≈3-fold increases in TF activity in the medium. Release of TF into the medium was dependent on the presence of the TF transmembrane domain but not the cytoplasmic domain. Antibodies to TF precipitated most of the activity from the culture medium, whereas antibodies to the &bgr;1-integrin subunit precipitated ≈33% of the activity. Treatment with detergent or phosphatidylserine:phosphatidylcholine did not increase activity, suggesting that all TF released by SMCs was in the appropriate lipid milieu and not encrypted. Western blotting showed that the medium contained full-length TF protein. Fluorescent cytometry showed that extracellular TF was present largely in particles ≤200 nm, which had a density of 1.10 g/mL. We hypothesize that active extracellular TF found in the injured arterial wall and atherosclerotic plaques derives, in part, from SMC microparticles.(Circ Res. 2000;87:126-132.)

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID