摘要:

Abstract—The effects of &agr;-adrenergic receptor (&agr;-AR) stimulation alone and the effects in the presence of &bgr;-adrenergic receptor (&bgr;-AR) stimulation were examined on L-type Ca2+currents (ICa-L) in the absence and presence of hypoxia. The &agr;-AR agonist methoxamine either had no effect or had a slight inhibitory effect on basalICa-Lin the absence and presence of hypoxia. Hypoxia significantly decreased theK0.5for activation ofICa-Lby norepinephrine from 79.8±6.6 to 13.3±0.7 nmol/L. To determine whether hypoxia specifically altered the sensitivity of the channel to &agr;-AR stimulation, cells were exposed to increasing concentrations of methoxamine in the presence of 100 nmol/L isoproterenol (Iso).In the absence of hypoxia, methoxamine inhibited the Iso-activatedICa-Lin a concentration-dependent manner with an EC50of 86.9±9.9 &mgr;mol/L. However, in the presence of hypoxia, the EC50for inhibition ofICa-Lby methoxamine was significantly increased to 266.7±10.8 &mgr;mol/L. Methoxamine had little effect onICa-Lactivated by forskolin or histamine in the absence or presence of hypoxia. In addition, inhibition of protein kinase C by bisindolylmaleimide 1 or protein kinase C &bgr; peptide inhibitor had no effect on the methoxamine-induced antagonism ofICa-Lin the absence or presence of hypoxia. The tyrosine kinase inhibitor genistein attenuated the methoxamine response in nonhypoxic cells only. However, during hypoxia it was attenuated with the phospholipase A2inhibitors mepacrine and indomethacin. These findings represent a novel regulation of the L-type Ca2+channel by the phospholipase A2pathway and illustrate the complexity of regulation of the channel under hypoxic conditions.

ISSN:0009-7330    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Abstract—We have previously demonstrated that thrombin upregulation of insulin-like growth factor-1 receptor (IGF-1R) is essential for thrombin-induced mitogenic signaling. To characterize the mechanisms involved, we studied transcription of the IGF-1R gene in rat aortic smooth muscle cells. Thrombin markedly increased IGF-1R mRNA levels, peaking at 3 hours (112±7% above control). This effect was mimicked by the hexapeptide SFFLRN (that functions as a tethered ligand) and was blocked by the thrombin inhibitor hirudin. Nuclear run-on assays indicated that thrombin stimulated IGF-1R gene transcription by 2.1-fold, and this was confirmed with the use of actinomycin D. Thrombin-mediated upregulation of IGF-1R mRNA and protein levels was protein kinase C independent but was completely inhibited by the protein tyrosine kinase inhibitor genistein and by the antioxidantsN-acetyl-l-cysteine and pyrrolidinedithiocarbamate, suggesting the involvement of reactive oxygen species. The thrombin-induced increase in IGF-1R mRNA was inhibitable by diphenyleneiodonium chloride but not by other inhibitors of cellular oxidase systems, suggesting that NAD(P)H oxidase was necessary for the increase. Furthermore, inhibitors of the epidermal growth factor receptor kinase, Janus kinase-2 kinase, and Src kinase did not block the effect. Thus, thrombin transcriptionally regulates the IGF-1R gene via a redox-sensitive protein tyrosine kinase–dependent pathway that does not require protein kinase C activation. In view of our prior data indicating that IGF-1R density is a critical determinant of vascular smooth muscle cell growth, our findings have particular relevance to understanding mechanisms whereby growth factors such as thrombin regulate vascular proliferation in vivo.

ISSN:0009-7330    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Abstract—The fruit fly,Drosophila melanogaster, has served as a valuable model/organism for the study of aging and was the first organism possessing a circulatory system to have its genome completely sequenced. However, little is known about the function of the heartlike organ of flies during the aging process. We have developed methods for studying cardiac function in vivo in adult flies. Using 2 different cardiovascular stress methods (elevated ambient temperature and external electrical pacing), we found that maximal heart rate is significantly and reproducibly reduced with aging inDrosophila, analogous to observations in elderly humans. We also describe for the first time several other aspects of the cardiac physiology of young adult and agingDrosophila, including an age-associated increase in rhythm disturbances. These observations suggest that the study of declining cardiac function in aging flies may serve as a genetically tractable model for genome-wide mutational screening for genes that participate in or protect against cardiac aging and disease.

ISSN:0009-7330    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Abstract—Phosphorylation of cardiac myofibrils by cAMP-dependent protein kinase (PKA) can increase the intrinsic rate of myofibrillar relaxation, which may contribute to the shortening of the cardiac twitch during &bgr;-adrenoceptor stimulation. However, it is not known whether the acceleration of myofibrillar relaxation is due to phosphorylation of troponin I (TnI) or of myosin binding protein-C (MyBP-C). To distinguish between these possibilities, we used transgenic mice that overexpress the nonphosphorylatable, slow skeletal isoform of TnI in the myocardium and do not express the normal, phosphorylatable cardiac TnI. The intrinsic rate of relaxation of myofibrils from wild-type and transgenic mice was measured using flash photolysis of diazo-2 to rapidly decrease the [Ca2+] within skinned muscles from the mouse ventricles. Incubation with PKA nearly doubled the intrinsic rate of myofibrillar relaxation in muscles from wild-type mice (relaxation half-time fell from ≈150 to ≈90 ms at 22°C) but had no effect on the relaxation rate of muscles from the transgenic mice. In parallel studies with intact muscles, we assessed crossbridge kinetics indirectly by determiningfmin(the frequency for minimum dynamic stiffness) during tetanic contractions. Stimulation of &bgr;-adrenoceptors with isoproterenol increasedfminfrom 1.9 to 3.1 Hz in muscles from wild-type mice but had no effect onfminin muscles from transgenic mice. We conclude that the acceleration of myofibrillar relaxation rate by PKA is due to phosphorylation of TnI, rather than MyBP-C, and that this may be due, at least in part, to faster crossbridge cycle kinetics.

ISSN:0009-7330    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Abstract—Deamination of adenosine on pre-mRNA to inosine is a recently discovered process of posttranscription modification of pre-mRNA, termed A-to-I RNA editing, which results in the production of proteins not inherent in the genome. The present study aimed to identify a role for A-to-I RNA editing in the development of microvascular lung injury. To that end, the pulmonary expression and activity of the RNA editase ADAR1 were evaluated in a mouse model of endotoxin (15 mg/kg IP)–induced microvascular lung injury (n=5) as well as in cultured alveolar macrophages stimulated with endotoxin, live bacteria, or interferon. ADAR1 expression and activity were identified in sham lungs that were upregulated in lungs from endotoxin-treated mice (at 2 hours). Expression was localized to polymorphonuclear and monocytic cells. These events preceded the development of pulmonary edema and leukocyte accumulation in lung tissue and followed the local production of interferon-&ggr;, a known inducer of ADAR1 in other cell systems. ADAR1 was found to be upregulated in alveolar macrophages (MH-S cells) stimulated with endotoxin (1 to 100 &mgr;g/mL), liveEscherichia coli(5×107colony-forming units), or interferon-&ggr; (1000 U/mL). Taken together, these data suggest that ADAR1 may play a role in the pathogenesis of microvascular lung injury possibly through induction by interferon.

ISSN:0009-7330    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Abstract—Using B2kinin receptor gene knockout mice (B2−/−), we tested the hypothesis that (l) lack of B2receptors may affect blood pressure and cardiac function and aggravate cardiac remodeling after myocardial infarction (MI), and (2) kinins partially mediate the cardiac beneficial effect of angiotensin-converting enzyme inhibitors (ACEi) or angiotensin II type 1 receptor antagonists (AT1-ant), whereas lack of B2receptors may diminish this cardioprotective effect. Chronic heart failure (HF) was induced by MI, which was caused by coronary artery ligation in both B2−/−and 129/SvEvTac mice (wild-type control, B2+/+). An ACEi (ramipril, 2.5 mg/kg/d) or AT1-ant (L-158809, 3 mg/kg/d) was given 1 week after MI and was continued for 12 weeks. Left ventricular (LV) ejection fraction, cardiac output (CO), diastolic LV dimension (LVDd), and LV mass were evaluated by echocardiography. Myocyte cross-sectional area and interstitial collagen fraction were studied histopathologically. We found that basal blood pressure and cardiac function were similar in B2+/+and B2−/−mice. After MI, development of HF and remodeling were also similar between the 2 strains. The ACEi improved cardiac function and remodeling in both strains; however, its effects were attenuated in B2−/−mice (respective values for B2+/+versus B2−/−mice: overall increase in ejection fraction, 64±10% versus 21±5% [P<0.01]; increase in CO, 69±17% versus 23±9% [P<0.01]; overall decrease in LVDd, −24±3% versus −7±4% [P<0.01]; and decrease in LV mass, −38±3% versus −6±6% [P<0.01]). AT1-ant had a beneficial cardiac effect similar to that produced by ACEi, and this effect was also diminished in B2−/−mice (respective values for B2+/+versus B2−/−mice: overall increase in ejection fraction, 46±10% versus 25±9% [P<0.01]; increase in CO, 44±14% versus 15±5% [P<0.01]; overall decrease in LVDd, −14±4% versus −6±3% [P<0.01]; and decrease in LV mass, −33±4 versus −16±7% [P<0.01]). The effect of ACEi or AT1-ant on myocyte cross-sectional area was similar between strains; however, their effect on the interstitial collagen fraction was diminished in B2−/−mice. We concluded that (1) lack of B2kinin receptors does not affect cardiac phenotype or function, either under normal physiological conditions or during the development of HF; and (2) kinins acting via the B2receptor play an important role in the cardioprotective effect of ACEi and AT1-ant.

ISSN:0009-7330    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Abstract—Osteopontin (OPN), an extracellular matrix protein, is expressed in the myocardium with hypertrophy and failure. We tested the hypothesis that OPN plays a role in left ventricular (LV) remodeling after myocardial infarction (MI). Accordingly, OPN expression and LV structural and functional remodeling were determined in wild-type (WT) and OPN knockout (KO) mice 4 weeks after MI. Northern analysis showed increased OPN expression in the infarcted region, peaking 3 days after MI and gradually decreasing over the next 28 days. In the remote LV, OPN expression was biphasic, with peaks at 3 and 28 days. In situ hybridization and immunohistochemical analyses showed increased OPN mRNA and protein primarily in the interstitium. Infarct size, heart weight, and survival were similar in KO and WT mice after MI (P=NS), whereas the lung wet weight/dry weight ratio was increased in the KO mice (P<0.005 versus sham-operated mice). Peak LV developed pressure was reduced to a similar degree after MI in the KO and WT mice. The number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive myocytes was similar in KO and WT mice after MI. In contrast, post-MI LV chamber dilation was approximately twice as great in KO versus WT mice (P<0.001). Myocyte length increased after MI in WT mice (P<0.001) but not in KO mice. Electron microscopy showed increased collagen content in WT mice after MI but not in KO mice after MI. Type I collagen content was increased ≈3-fold and ≈7-fold in remote and infarcted regions, respectively, of WT hearts after MI but not in KO hearts (P<0.01 versus WT hearts). Likewise, Northern analyses showed increased collagen I(&agr;1) mRNA after MI in remote regions of WT hearts but not in KO hearts. Thus, increased OPN expression plays an important role in regulating post-MI LV remodeling, at least in part, by promoting collagen synthesis and accumulation.

ISSN:0009-7330    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Abstract—Heme oxygenase (HO) is a cytoprotective enzyme that degrades heme (a potent oxidant) to generate carbon monoxide (a vasodilatory gas that has anti-inflammatory properties), bilirubin (an antioxidant derived from biliverdin), and iron (sequestered by ferritin). Because of properties of HO and its products, we hypothesized that HO would be important for the regulation of blood pressure and ischemic injury. We studied chronic renovascular hypertension in mice deficient in the inducible isoform of HO (HO-1) using a one kidney-one clip (1K1C) model of disease. Systolic blood pressure was not different between wild-type (HO-1+/+), heterozygous (HO-1+/−), and homozygous null (HO-1−/−) mice at baseline. After 1K1C surgery, HO-1+/+mice developed hypertension (140±2 mm Hg) and cardiac hypertrophy (cardiac weight index of 5.0±0.2 mg/g) compared with sham-operated HO-1+/+mice (108±5 mm Hg and 4.1±0.1 mg/g, respectively). However, 1K1C produced more severe hypertension (164±2 mm Hg) and cardiac hypertrophy (6.9±0.6 mg/g) in HO-1−/−mice. HO-1−/−mice also experienced a high rate of death (56%) within 72 hours after 1K1C surgery compared with HO-1+/+(25%) and HO-1+/−(28%) mice. Assessment of renal function showed a significantly higher plasma creatinine in HO-1−/−mice compared with HO-1+/−mice. Histological analysis of kidneys from 1K1C HO-1−/−mice revealed extensive ischemic injury at the corticomedullary junction, whereas kidneys from sham HO-1−/−and 1K1C HO-1+/−mice appeared normal. Taken together, these data suggest that chronic deficiency of HO-1 does not alter basal blood pressure; however, in the 1K1C model an absence of HO-1 leads to more severe renovascular hypertension and cardiac hypertrophy. Moreover, renal artery clipping leads to an acute increase in ischemic damage and death in the absence of HO-1.

ISSN:0009-7330    

出版商:OVID    

年代:2001

数据来源: OVID