摘要:

Since the cloning of the first inwardly rectifying K sup plus channel in 1993, a family of related clones has been isolated, with many members being expressed in the heart. Exogenous expression of different clones has demonstrated that between them they encode channels with the essential functional properties of classic inward rectifier channels, ATP-sensitive Kpluschannels, and muscarinic receptor-activated inward rectifier channels. High-level expression of cloned channels has led to the discovery that classic strong inward, or anomalous, rectification is caused by very steeply voltage-dependent block of the channel by polyamines, with an additional contribution by Mg2plus ions. Knowledge of the primary structures of inward rectifying channels and the ability to mutate them have led to the determination of many of the structural requirements of inward rectification. The implications of these advances for basic understanding and pharmacological manipulation of cardiac excitability may be significant. For example, cellular concentrations of polyamines are altered under different conditions and can be manipulated pharmacologically. Simulations predict that changes in polyamine concentrations or changes in the relative proportions of each polyamine species could have profound effects on cardiac excitability.(Circ Res. 1996; 78:1-7.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

To elucidate the regulation of very-low-density lipoprotein (VLDL) receptor, we have studied its gene expression in the heart of spontaneously hypertensive rats-stroke prone (SHR-SP, an animal model for hypertension-induced cardiac hypertrophy) compared with Wistar-Kyoto rats. RNase protection assay showed that ventricular VLDL receptor mRNA falls to 41% of normal levels at 4 weeks, when hypertension is not yet fully developed, and drops further to 14% at 13 weeks, when cardiac hypertrophy is established. Lipoprotein lipase mRNA decreases in parallel with VLDL receptor mRNA. In cultured neonatal rat ventricular cardiomyocytes, VLDL receptor mRNA decreases in parallel with the process of cardiocyte hypertrophy during the 24 hours after treatment with 10minus8 mol/L endothelin-1, falling to 40% of the initial value. These results demonstrate that there is downregulation of VLDL receptor gene expression in cardiac hypertrophy both in vivo and in vitro and suggest that the regulation of the VLDL receptor is possibly linked with the switch in energy substrate from lipid to glucose known to occur in cardiac hypertrophy.(Circ Res. 1996;78:8-14.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

We have isolated murine embryonic atrial and ventricular cells derived from timed-pregnant females at different periods and used patch-clamp procedures to investigate age- and chamber-specific expression of ionic channels in the developing fetal mouse. Our data indicate that L-type Ca2plus channels play a dominant role in excitation during early murine cardiac embryogenesis and that Napluschannel expression increases dramatically just before birth. Kpluschannel expression is particularly sensitive to changes during development. Neither atrial nor ventricular cells express a slowly activating component of delayed rectification (IKs) until just before birth, and inwardly rectifying channel activity, associated with determination of cellular resting potential, is not markedly apparent until late stages of embryogenesis. Instead, we find robust expression of the ATP-regulated Kpluschannel at early and late stages of embryonic development, which may indicate a novel functional role for this channel during morphogenesis of the heart. These results have important implications for the physiology and development of the murine cardiac conduction system and will also serve as a baseline for future studies designed to investigate developmental changes of ion channel expression in the myocardium of both wild-type and genetically modified mice.(Circ Res. 1996;78:15-25.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Because the number and characteristics of delayed rectifier K sup plus current (I sub K) components vary between species, the role of each component in the action potential and modulation by class III agents is uncertain. To address these issues, IKwas assessed in adult isolated canine ventricular and atrial myocytes by using whole-cell and perforated-patch techniques. IKcomponents were characterized by using two complementary approaches: a kinetic approach (based on biexponential fits to deactivating tail currents) and a pharmacological approach (using the methanesulfonanilide compound E-4031). In ventricular myocytes, two exponential tail current components were distinguished; these components differed in the voltage and time dependence of activation and the effect of lower [Kplus]o. Both kinetic components contributed equally to peak tail current amplitude (measured at minus 35 mV) after a single 300-ms pulse to 5 mV, simulating an action potential. By use of E-4031, rapidly and slowly activating components of IK(IKrand IKs, respectively) that were analogous to tail components described kinetically were identified. The activation kinetics and rectification properties of canine IKrand IKsare qualitatively similar to those described previously for guinea pigs. In contrast, canine IKrand IKsdeactivation kinetics differed markedly from those found in guinea pigs, with canine IKrdeactivating slowly (time constant tau, 2 to 3 s near minus 35 mV) and IKsdeactivating rapidly (tau, 150 ms near minus 35 mV and decreasing to 30 ms near minus 85 mV). E-4031 elicited reverse rate-dependent effects (greater drug-induced prolongation of the action potential at slower stimulation rates); this effect is inconsistent with the hypothesis attributing reverse rate dependence to incomplete IKsdeactivation during rapid stimulation (due to rapid deactivation of canine IKs). Two IKcomponents with characteristics comparable to those found in ventricular myocytes were also observed in atrial myocytes. In conclusion, (1) IKr- and IKs-like components of IKare present in canine atrial and ventricular myocytes, with deactivation kinetics strikingly different from those found in guinea pigs, and (2) the rapid deactivation kinetics of canine IKsdo not support its role in reverse rate dependence with class III agents in this species.(Circ Res. 1996;78:26-37.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Smooth muscle cell (SMC) migration and replication are important for neointimal formation after arterial injury. Migration of SMCs requires degradation of basement membrane and extracellular matrix surrounding the cell, and our previous work has shown a correlation between expression of two matrix-degrading metalloproteinases (MMPs), MMP-2 and MMP-9, and smooth muscle migration into the intima in the balloon catheter-injured rat carotid artery. In the present study, an MMP inhibitor, GM 6001, was administered to rats for various times after balloon injury of the carotid artery. Inhibition of MMP activity resulted in a 97% decrease in the number of SMCs that migrated into the intima by 4 days after injury, and lesion growth was retarded by continuous treatment with GM 6001 for up to 10 days after injury. At 10 days, intimal area in GM 6001-treated rats was 0.035 plus minus 0.008 mm2compared with 0.095 plus minus 0.01 mm2in the control group. Neither intimal nor medial SMC replication rates were decreased by GM 6001 treatment, supporting our hypothesis that the decrease in lesion size was due to inhibition of MMP-mediated migration and not inhibition of replication. By 14 days after injury, however, intimal area and SMC number were the same in control and inhibitor-treated rats. An increased rate of SMC replication in the GM 6001 rats (replication rates at 10 days were 56.7 plus minus 10.0% in the GM 6001 group and 16.97 plus minus 1.73% in the control group) contributed to ``catch-up'' growth of the neointima. Thus, it appears that inhibiting SMC migration with MMP inhibitors is not sufficient to inhibit lesion growth, and lesion size eventually catches up to control via increased SMC replication.(Circ Res. 1996;78:38-43.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Plasmin and matrix metalloproteinases (MMPs) both participate in extracellular matrix remodeling. This study examined the effects of tumor necrosis factor-alpha (TNF-alpha) and plasminogen on collagenase, stromelysin, and plasminogen activator inhibitor-1 (PAI-1) synthesis by cultured human vascular smooth muscle cells (SMCs). TNF-alpha induced the concentration-dependent synthesis of collagenase and stromelysin, which remained predominantly in proenzyme forms, as determined by Western analysis of culture media. In contrast, plasminogen and plasmin not only increased secretion of MMPs but also induced cleavage to their active forms. The serine protease inhibitor aprotinin inhibited this activation of MMPs by plasminogen and plasmin. TNF-alpha reduced plasminogen-induced activation of MMPs, suggesting induction of an inhibitor of plasmin generation, such as PAI-1. Enzyme-linked immunosorbent assay of culture media showed that TNF-alpha (10 ng/mL) increased PAI-1 secretion by 4.2-fold compared with control (105.5 plus minus 9.6 versus 24.9 plus minus 1.7 ng/mL, n equals 3). Surprisingly, plasminogen also increased PAI-1 secretion by vascular SMCs (3.6-fold over control). These results demonstrate coordination of cytokines and serine proteases in regulating MMP secretion and activation. In addition, the induction of PAI-1 by TNF-alpha and plasminogen suggests a negative-feedback mechanism to limit both plasmin-mediated and MMP-mediated matrix degradation.(Circ Res. 1996;78:44-49.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Although a decrease in extravascular pH has been suggested to be involved in coronary flow regulation during hypoxia, ischemia, and increased metabolic demand of the heart, its vasomotor control mechanism has not been elucidated. To examine the effect of acidosis on vasomotor tone, porcine coronary arterioles (40 to 110 micro meter) were isolated, cannulated, and pressurized to 60 cm H2O intraluminal pressure without flow for in vitro study. Acidosis (pH 7.4 to 7.0) was produced by adding HCl to the extravascular solution. The involvement of potassium channels in the vasomotor response to acidosis was evaluated by using BaCl2(100 mu mol/L, nonspecific potassium channel inhibitor), glibenclamide (5 mu mol/L, ATP-sensitive potassium channel inhibitor), and iberiotoxin (100 nmol/L, calcium-activated potassium channel inhibitor). To determine whether endothelial hyperpolarization contributes to the acidosis-induced dilation, the pH-diameter relation of the vessel was examined under a high intraluminal concentration of KCl (40 mmol/L). The involvement of nitric oxide and prostaglandins was assessed by using NG-monomethyl-L-arginine (L-NMMA, 10 mu mol/L) and indomethacin (10 mu mol/L), respectively. To evaluate the role of endothelium in the acidosis-induced dilation, the pH-diameter relation was studied after endothelial removal. All vessels developed a similar level of spontaneous tone (internal diameter, 75 plus minus 4 micro meter [approximate equal 69 plus minus 1% of maximum diameter]) and dilated to HCl in a dose-dependent manner. Glibenclamide completely abolished vasodilation to a mild level of acidosis (pH 7.2 to 7.3) and attenuated the vasodilation by 70% at pH 7.0. Acidosis-induced dilation was also inhibited by BaCl2but not by iberiotoxin. L-NMMA, indomethacin, and intraluminal KCl did not alter the pH-diameter relation. Vasodilation to acidosis of the endotheliumdenuded vessels was identical to that of the endothelium-intact vessels. In addition, glibenclamide attenuated the acidosisinduced arteriolar dilation of endothelium-denuded vessels in a manner similar to that of endothelium-intact vessels. These results suggest that the opening of ATP-sensitive potassium channels in vascular smooth muscle mediates the coronary arteriolar dilation during acidosis.(Circ Res. 1996;78:50-57.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Endothelium-dependent responses are depressed in coronary and peripheral blood vessels after the onset of pacing-induced heart failure in dogs and heart failure of various etiologies in humans. The present study was designed to examine whether these responses were due to decreases in the expression of endothelial cell NO synthase (ecNOS) and cyclooxygenase-1 (COX-1). After 1 month of left ventricular pacing, 8 mongrel dogs were monitored for heart failure as defined by clinical signs and left ventricular end diastolic pressures more than 25 mm Hg. Total RNA and protein were isolated from endothelial cells scraped from the thoracic aorta and analyzed by Northern and Western blotting, respectively. Blots probed with32P-labeled cDNAs for ecNOS and COX-1 were quantified densitometrically, and results were normalized against GAPDH or von Willebrand factor (vWF). In arbitrary units, the ratios of ecNOS to GAPDH were 2.66 plus minus 0.77 (mean plus minus SEM, n equals 17) and 1.12 plus minus 0.37 (n equals 6), and the ratios of COX-1 to GAPDH were 1.52 plus minus 0.52 and 0.56 plus minus 0.15 before and after heart failure, respectively. These represent 56% to 64% (P less than .05) reductions in ecNOS and COX-1 gene expression. There was no change in the ratios of either COX-1 or ecNOS to vWF. There was also a marked reduction in ecNOS protein after heart failure, estimated at 70%. A marked reduction in nitrite production, a measure of enzyme activity, from thoracic aortas in response to stimulation by either acetylcholine or bradykinin also occurred. To determine whether ecNOS and COX-1 could be independently regulated, an orally active NO-releasing agent, CAS 936, was given to 7 normal dogs for 7 days, and aortic ecNOS and COX-1 mRNAs were analyzed. The ratio of ecNOS to GAPDH was depressed by 52% (P less than .05) in aortas from these dogs, wherease the ratio of COX-1 to GAPDH was unchanged. Similar results were found when data were normalized to vWF. These results suggest that at least two endothelial vasodilator gene products are reduced in heart failure, as opposed to a selective defect in NO synthase gene expression.(Circ Res. 1996;78:58-64.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

With the knowledge of NO as an antiadhesion molecule, we performed studies to investigate the effects of NO on postischemic polymorphonuclear leukocyte (PMN)-mediated myocardial contractile dysfunction. Studies were performed with isolated perfused rat hearts subjected to 20 minutes of global ischemia and 45 minutes of reperfusion. Human PMNs (50 million) were infused over the first 5 minutes of reperfusion, and the recovery of left ventricular function was compared with baseline values. Infusion of PMNs alone (n equals 10) led to a 61% reduction in left ventricular developed pressure (LVDP) and a 57% reduction in the pressure-rate product (PRP) at 45 minutes of reperfusion. Infusion of an NO donor, CAS-754 (n equals 9), resulted in 80.2 plus minus 6.7% recovery of LVDP and 77.0 plus minus 8.6% recovery of PRP. Treatment with L-arginine (2.5 mmol/L, n equals 10) resulted in a similar improvement in the postischemic contractile state of the heart. In contrast, NG-nitro-L-arginine methyl ester (L-NAME) treatment (250 mu mol/L, n equals 10) resulted in an exacerbation of contractile dysfunction, as evidenced by a 93% reduction in LVDP at 45 minutes of reperfusion and a 91% reduction in PRP. The deleterious effects of L-NAME were prevented by L-arginine coperfusion. We failed to observe any cardioprotective effects when NO or L-arginine was administered to hearts subjected to 25 minutes of ischemia and 45 minutes of reperfusion in the absence of PMNs. In conclusion, PMN-mediated myocardial contractile dysfunction is attenuated by NO and exacerbated by blockade of NO synthesis.(Circ Res. 1996;78:65-72.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

We tested the hypothesis that anoxic preconditioning could protect coronary endothelial cells against anoxic and reoxygenation injury and that this preconditioning effect could be mediated by an adenosine A sub 2 receptor via the protein kinase C (PKC) pathway. Cells were preconditioned with 10-minute anoxia and 10-minute reoxygenation and were then subjected to anoxia for 60 minutes, followed by 120 minutes of reoxygenation. In some groups, the preconditioning effect was prevented by 8-sulfophenyltheophylline (SPT [50 mu mol/L], a nonselective adenosine receptor antagonist) or calphostin C (100 nmol/L, a PKC inhibitor). In other groups, 2-p-(2-carboxyethyl)phenethylamino-5 prime-N-ethylcarboxamidoadenosine (CGS-21680 [20 nmol/L], an adenosine A2receptor agonist), R-(minus)-N6-(2-phenylisopropyl)-adenosine (R-PIA [50 nmol/L], an adenosine A1receptor agonist), or 4 beta -phorbol 12-myristate 13-acetate (PMA [100 nmol/L], a PKC activator) was given as a pretreatment to mimic the preconditioning effect. Endothelial cells were also pretreated with 100 nmol/L calphostin C to confirm whether inhibition of PKC can block the effects of adenosine A2receptor activation by CGS-21680 on anoxia and reoxygenation injury. Preconditioning reduced LDH release, increased adenosine release, promoted translocation of PKC from cytosol to membrane, increased cell viability, and preserved ATP content and cell morphology. Pretreatment with either CGS-21680 or PMA resulted in protection similar to that seen with anoxic preconditioning. The protection was totally abolished by SPT or calphostin C. The results suggest that (1) preconditioning protects coronary endothelial cells against anoxia and reoxygenation injury, (2) the protection is probably mediated by activation of adenosine A2receptors through the PKC pathway, and (3) the preservation of endothelial cells may be one of the mechanisms of myocardial preconditioning.(Circ Res. 1996;78:73-81.)

ISSN:0009-7330    

出版商:OVID    

年代:1996

数据来源: OVID