摘要:

AbstractAlthough the cationic inward rectifiers (Kir and hyperpolarization-activatedIfchannels) have been well characterized in cardiac myocytes, the expression and physiological role of anionic inward rectifiers in heart are unknown. In the present study, we report the functional and molecular identification of a novel chloride (Cl−) inward rectifier (Cl.ir) in mammalian heart. Under conditions in which cationic inward rectifier channels were blocked, membrane hyperpolarization (−40 to −140 mV) activated an inwardly rectifying whole-cell current in mouse atrial and ventricular myocytes. Under isotonic conditions, the current activated slowly with a biexponential time course (time constants averaging 179.7±23.4 [mean±SEM] and 2073.6±287.6 ms at −120 mV). Hypotonic cell swelling accelerated the activation and increased the current amplitude whereas hypertonic cell shrinkage inhibited the current. The inwardly rectifying current was carried by Cl−(ICl.ir) and had an anion permeability sequence of Cl−>I−≫aspartate.ICl.irwas blocked by 9-anthracene-carboxylic acid and cadmium but not by stilbene disulfonates and tamoxifen. A similarICl.irwas also observed in guinea pig cardiac myocytes. The properties ofICl.irare consistent with currents generated by expression of ClC-2 Cl−channels. Reverse transcription polymerase chain reaction and Northern blot analysis confirmed transcriptional expression of ClC-2 in both atrial and ventricular tissues and isolated myocytes of mouse and guinea pig hearts. These results indicate that a novelICl.iris present in mammalian heart and support a potentially important role of ClC-2 channels in the regulation of cardiac electrical activity and cell volume under physiological and pathological conditions. The full text of this article is available at http://www.circresaha.org.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractThe rabbit inferior vena cava (IVC) is a large-capacitance vessel that displays typical contractile dose-response curves for caffeine and phenylephrine (PE). Using confocal microscopy on the endothelium-denuded IVC, we undertook experiments to correlate these whole-tissue contractile dose-response curves with changes in subcellular [Ca2+]isignals in the in situ vascular smooth muscle cells (VSMCs). We observed that both caffeine and PE initially elicited Ca2+waves in individual VSMCs. The [Ca2+]iin cells challenged with caffeine subsequently returned to baseline whereas the [Ca2+]iin cells challenged with PE exhibited repetitive asynchronous Ca2+waves. These [Ca2+]ioscillations were related to Ca2+release from the sarcoplasmic reticulum as they were inhibited by ryanodine and caffeine. The lack of synchronicity of the [Ca2+]ioscillations between VSMCs can explain the observed tonic contraction at the whole-tissue level. The nature of these Ca2+waves was further characterized. For caffeine, the amplitude was all-or-none in nature, with individual cells differing in sensitivity, leading to their recruitment at different concentrations of the agonist. This concentration dependency of recruitment appears to form the basis for the concentration dependency of caffeine-induced contraction. Furthermore, the speed of the Ca2+waves correlated positively with the concentration of caffeine. In the case of PE, we observed the same characteristics with respect to wave speed, amplitude, and recruitment. Increasing concentrations of PE also enhance the frequency of the [Ca2+]ioscillations. We therefore conclude that PE stimulates whole-tissue contractility through differential recruitment of VSMCs and enhancement of the frequency of asynchronous [Ca2+]ioscillations once the cells are recruited. The full text of this article is available at http://www.circresaha.org.

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

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:

AbstractOnly scarce information is available on the activity and modifications of the cardiac endothelin (ET)–1 system in heart failure due to ischemic (ICM) or idiopathic dilated (DCM) cardiomyopathy. The activity of the ET-1 system was investigated by measuring cardiac ET-1 and big ET-1 formation and quantifying cardiac mRNA for prepro–ET-1 (ppET-1), ET-converting enzyme-1, and ETAand ETBreceptors both in myocardium and in isolated myocytes using Northern blot, reverse transcription–polymerase chain reaction, and in situ hybridization in 22 patients with DCM and 20 with ICM who underwent cardiac transplantation and in 7 potential heart transplant donors (nonfailing hearts). Notwithstanding a similar increase of plasma ET-1 in the 2 groups, cardiac ET formation, mRNA levels for ppET-1, and ETAand ETBreceptors were higher on both the myocardium and isolated myocytes from ICM than on those from DCM hearts (P<0.001 for all). ppET-1 and ET-converting enzyme-1 mRNAs were expressed on myocytes and endothelial and interstitial cells in ICM, whereas in DCM and nonfailing hearts they were mainly expressed on nonmyocyte cells. In both ICM and DCM, the ETAmRNA signal was expressed on both myocytes and nonmyocyte cells, whereas ETBmRNA was almost exclusively localized on nonmyocyte cells. ETA- and ETB-specific receptor binding was increased on both myocytes and cardiac membranes, showing a positive correlation with left ventricular ejection fraction in ICM (r=0.78 and 0.70) but not in DCM patients. The present results show that human ventricular myocytes express all of the components of the ET-1 system, which is selectively upregulated in ICM patients and appears to be functionally important in the maintenance of cardiac function.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractIn the heart, the relative proportions of the 2 forms of the motor protein myosin heavy chain (MyHC) have been shown to be affected by a wide variety of pathological and physiological stimuli. Hearts that express the faster MyHC motor protein, &agr;, produce more power than those expressing the slower MyHC motor protein, &bgr;, leading to the hypothesis that MyHC isoforms play a major role in the determination of cardiac contractility. We showed previously that a significant amount of &agr;MyHC mRNA is expressed in nonfailing human ventricular myocardium and that &agr;MyHC mRNA expression is decreased 15-fold in end-stage failing left ventricles. In the present study, we determined the MyHC protein isoform content of human heart samples of known MyHC mRNA composition. We demonstrate that &agr;MyHC protein was easily detectable in 12 nonfailing hearts. &agr;MyHC protein represented 7.2±3.2% of total MyHC protein (compared with ≈35% of the MyHC mRNA), suggesting that translational regulation may be operative; in contrast, there was effectively no detectable &agr;MyHC protein in the left ventricles of 10 end-stage failing human hearts.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractA series of pro-oxidant and antioxidant enzymes, such as the NADPH oxidase system, maintain the redox state in the vessel wall. A major component of NADPH oxidase is p22phox, which is implicated in atherosclerosis. We prospectively studied the association of the histidine (H)72→tyrosine (Y) mutation in p22phoxwith the severity and progression/regression of coronary artery disease (CAD), plasma lipid levels, clinical events, and response to treatment with fluvastatin in a well-characterized population. Genotypes were determined by polymerase chain reaction and restriction digestion withRsaI enzyme in 368 subjects in the Lipoprotein and Coronary Atherosclerosis Study (LCAS). Fasting plasma lipids and quantitative coronary angiograms were obtained at baseline and 2.5 years after randomization to fluvastatin or placebo. Subjects with CC genotype (n=157) were identified by the presence of 396-bp and 113-bp products on gel electrophoresis. Those with TT (n=39) were identified by the presence of 316-bp, 113-bp, and 80-bp products, and those with CT (n=172) by the presence of 396-bp, 316-bp, 113-bp, and 80-bp products. Baseline and final plasma levels of lipids and the baseline severity of CAD were not significantly different among the genotypes. In the placebo group, subjects with the mutation had a 3- to 5-fold greater loss in mean minimum lumen diameter (MLD) (TT: −0.15±0.15; CT: −0.17±0.26; and CC: −0.03±0.22 mm;P=0.006) and lesion-specific MLD (TT: −0.15±0.06; CT: −0.18±0.03; and CC: −0.06±0.03 mm;P=0.038) than those without. Progression was also more (TT: 8/17 [47%]; CT: 35/73 [48%]; and CC: 17/62 [27%]) and regression less (TT: 0/17 [0%]; CT: 1/73 [1%]; and CC: 11/72 [18%]) common in those with the mutation (P=0.002). The C242T mutation in p22phox, involved in maintaining the redox state in the vessel wall, is associated with progression of coronary atherosclerosis in the LCAS population.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

AbstractThe heterogeneous distribution of ion channels in ventricular muscle gives rise to spatial variations in action potential (AP) duration (APD) and contributes to the repolarization sequence in healthy hearts. It has been proposed that enhanced dispersion of repolarization may underlie arrhythmias in diseases with markedly different causes. We engineered dominant negative transgenic mice that have prolonged QT intervals and arrhythmias due to the loss of a slowly inactivating K+current. Optical techniques are now applied to map APs and investigate the mechanisms underlying these arrhythmias. Hearts from transgenic and control mice were isolated, perfused, stained with di-4-ANEPPS, and paced at multiple sites to optically map APs, activation, and repolarization sequences at baseline and during arrhythmias. Transgenic hearts exhibited a 2-fold prolongation of APD, less shortening (8% versus 40%) of APDs with decreasing cycle length, altered restitution kinetics, and greater gradients of refractoriness from apex to base compared with control hearts. A premature impulse applied at the apex of transgenic hearts produced sustained reentrant ventricular tachycardia (n=14 of 15 hearts) that did not occur with stimulation at the base (n=8) or at any location in control hearts (n=12). In transgenic hearts, premature impulses initiated reentry by encountering functional lines of conduction block caused by enhanced dispersion of refractoriness. Reentrant VT had stable (>30 minutes) alternating long/short APDs associated with long/short cycle lengths and T wave alternans. Thus, optical mapping of genetically engineered mice may help elucidate some electrophysiological mechanisms that underlie arrhythmias and sudden death in human cardiac disorders.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID