摘要:

Heterozygous mutations in the cardiac homeobox gene,NKX2-5, underlie familial cases of atrial septal defect (ASD) with severe atrioventricular conduction block. In this study, mice heterozygous forNkx2-5–null alleles were assessed for analogous defects. Although ASD occurred only rarely, atrial septal dysmorphogenesis was evident as increased frequencies of patent foramen ovale and septal aneurysm, and decreased length of the septum primum flap valve. These parameters were compounded by genetic background effects, and in the 129/Sv strain, septal dysmorphogenesis bordered on ASD in 17% ofNkx2-5heterozygotes. In a proportion of neonatal heterozygotes, as well as in adults with ASD, we found that the size of the foramen ovale was significantly enlarged and altered in shape, potentially exposing the normally thin septum primum to excessive hemodynamic forces. Therefore, defective morphogenesis of the septum secundum may be one contributing factor in the generation of patent foramen ovale, septal aneurysm, and certain ASDs. Mild prolongation of P-R interval in females and an increased frequency of stenotic bicuspid aortic valves were also features of theNkx2-5heterozygous phenotype. Our data demonstrate that the complex effects ofNkx2-5haploinsufficiency in mice are weaker but convergent with those in humans. As in the mouse, the phenotype of humanNKX2-5mutations may be modulated by interacting alleles.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

In the present study, we tested whether the &agr;1Asubunit, which encodes a neuronal isoform of voltage-dependent Ca2+channels (VDCCs) (P-/Q-type), was present and functional in vascular smooth muscle and renal resistance vessels. By reverse transcription–polymerase chain reaction and Southern blotting analysis, mRNA encoding the &agr;1Asubunit was detected in microdissected rat preglomerular vessels and vasa recta, in cultures of rat preglomerular vascular smooth muscle cells (VSMCs), and in cultured rat mesangial cells. With immunoblots, &agr;1Asubunit protein was demonstrated in rat aorta, brain, aortic smooth muscle cells (A7r5), VSMCs, and mesangial cells. Immunolabeling with an anti-&agr;1Aantibody was positive in acid-macerated, microdissected preglomerular vessels and in A7r5 cells. Patch-clamp experiments on aortic A7r5 cells showed 22±4% (n=6) inhibition of inward Ca2+current by &ohgr;-Agatoxin IVA (10–8mol/L), which in this concentration is a specific inhibitor of P-type VDCCs. Measurements of intracellular Ca2+in afferent arterioles with fluorescence-imaging microscopy showed 32±9% (n=10) inhibition of the K+-induced rise in Ca2+in the presence of 10–8mol/L &ohgr;-Agatoxin IVA. In microperfused rabbit afferent arterioles, &ohgr;-Agatoxin IVA inhibited depolarization-mediated contraction with an EC50of 10–17mol/L and complete blockade at 10–14mol/L. We conclude that the &agr;1Asubunit is expressed in VSMCs from renal preglomerular resistance vessels and aorta, as well as mesangial cells, and that P-type VDCCs contribute to Ca2+influx in aortic and renal VSMCs and are involved in depolarization-mediated contraction in renal afferent arterioles.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Parasympathetic stimulation of the heart acts through M2-muscarinic acetylcholine receptors to regulate ion channel activity and subsequent inotropic status. Although muscarinic signal transduction is mediated via pertussis toxin-sensitive G proteins G&agr;i/o, the specific signal transduction requirements of G&agr;i2and G&agr;i3in mediating muscarinic regulated L-type calcium currents (ICa, L), intracellular calcium, and cell contractility remain to be determined. Adult ventricular myocytes were isolated from G&agr;i2-null mice, G&agr;i3-null mice, and their wild-type littermates. Cell shortening, intracellular calcium levels, andICa, Lwere all measured in response to isoproterenol, a &bgr;-adrenergic receptor agonist, and carbachol, a cholinergic receptor agonist. With isoproterenol stimulation, myocytes from all groups demonstrated a marked increase in calcium currents, correlating with augmented intracellular calcium transient amplitude and cell shortening. Carbachol significantly attenuated the isoproterenol response in wild-type and G&agr;i3-null cells but had no effect in G&agr;i2-null cells. This study demonstrates that G&agr;i2, but not G&agr;i3, is required for muscarinic inhibition of the &bgr;-adrenergic response in adult murine ventricular myocytes.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

A tetrodotoxin-sensitive persistent sodium current,IpNa, was found in guinea pig ventricular myocytes by whole-cell patch clamping. This current was characterized in cells derived from the basal left ventricular subendocardium, midmyocardium, and subepicardium. Midmyocardial cells show a statistically significant (P<0.05) smallerIpNathan subendocardial and subepicardial myocytes. There was no significant difference inIpNacurrent density between subepicardial and subendocardial cells. Computer modeling studies support a role of this current in the dispersion of action potential duration across the ventricular wall.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Increased resistance to myocardial ischemia in chronically hypoxic immature rabbit hearts is associated with activation of ATP-sensitive K+(KATP) channels. We determined whether chronic hypoxia from birth alters the function of the mitochondrial KATPchannel. The KATPchannel opener bimakalim (1 &mgr;mol/L) increased postischemic recovery of left ventricular developed pressure in isolated normoxic (Fio2=0.21) hearts to values (42±4% to 67±5% ) not different from those of hypoxic controls but did not alter postischemic recovery of developed pressure in isolated chronically hypoxic (Fio2=0.12) hearts (69±5% to 72±5%). Conversely, the KATPchannel blockers glibenclamide (1 &mgr;mol/L) and 5-hydroxydecanoate (5-HD, 300 &mgr;mol/L) attenuated the cardioprotective effect of hypoxia but had no effect on postischemic recovery of function in normoxic hearts. ATP synthesis rates in hypoxic heart mitochondria (3.92±0.23 &mgr;mol ATP · min−1· mg mitochondrial protein−1) were significantly greater than rates in normoxic hearts (2.95±0.08 &mgr;mol ATP · min−1· mg mitochondrial protein−1). Bimakalim (1 &mgr;mol/L) decreased the rate of ATP synthesis in normoxic heart mitochondria consistent with mitochondrial KATPchannel activation and mitochondrial depolarization. The effect of bimakalim on ATP synthesis was antagonized by the KATPchannel blockers glibenclamide (1 &mgr;mol/L) and 5-HD (300 &mgr;mol/L) in normoxic heart mitochondria, whereas glibenclamide and 5-HD alone had no effect. In hypoxic heart mitochondria, the rate of ATP synthesis was not affected by bimakalim but was attenuated by glibenclamide and 5-HD. We conclude that mitochondrial KATPchannels are activated in chronically hypoxic rabbit hearts and implicate activation of this channel in the improved mitochondrial bioenergetics and cardioprotection observed.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

We previously showed that a premature stimulus can significantly alter vulnerability to arrhythmias by modulating spatial gradients of ventricular repolarization (ie, modulated dispersion). However, it is not clear if such changes in arrhythmia vulnerability can be attributed to the formation of an electrophysiological substrate for unidirectional block and what the potential role is of tissue structure in this process. Therefore, the main objective of the present study was to examine the concomitant effect repolarization gradients and tissue structure have on unidirectional block. Optical action potentials were recorded from 128 ventricular sites (1 cm2) in 8 Langendorff-perfused guinea pig hearts. Propagation was confined to the epicardial surface using an endocardial cryoablation procedure, and a 12-mm barrier with a 1.5-mm isthmus was etched with a laser onto the epicardium. A premature stimulus (S2) was delivered over a range of S1S2 coupling intervals to modulate repolarization gradients in a predictable fashion. When a second premature stimulus (S3) was delivered from the center of the isthmus, the occurrence and orientation of unidirectional block were highly dependent on repolarization gradients created by the S2 beat. In this model, a local repolarization gradient of 3.2 ms/mm was required for unidirectional block at this isthmus. In addition, the formation of unidirectional block was critically dependent on the presence of the source-sink mismatch imposed by the isthmus. These results may explain how the interplay between spatial heterogeneities of repolarization and tissue structure form a substrate for unidirectional block and reentry.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Connexin40 (Cx40) is a major gap junction protein that is expressed in the His-Purkinje system and thought to be a critical determinant of cell-to-cell communication and conduction of electrical impulses. Video maps of the ventricular epicardium and the proximal segment of the right bundle branch (RBB) were obtained using a high-speed CCD camera while simultaneously recording volume-conducted ECGs. In Cx40–/–mice, the PR interval was prolonged (47.4±1.4 in wild-type [WT] [n=6] and 57.5±2.8 in Cx40–/–[n=6];P<0.01). WT ventricular epicardial activation was characterized by focused breakthroughs that originated first on the right ventricle (RV) and then the left ventricle (LV). In Cx40–/–hearts, the RV breakthrough occurred after the LV breakthrough. Additionally, Cx40–/–mice showed RV breakthrough times that were significantly delayed with respect to QRS complex onset (3.7±0.7 ms in WT [n=6] and 6.5±0.7 ms in Cx40–/–[n=6];P<0.01), whereas LV breakthrough times did not change. Conduction velocity measurements from optical mapping of the RBB revealed slow conduction in Cx40–/–mice (74.5±3 cm/s in WT [n=7] and 43.7±6 cm/s in Cx40–/–[n=7];P<0.01). In addition, simultaneous ECG records demonstrated significant delays in Cx40–/–RBB activation time with respect to P time (P-RBB time; 41.6±1.9 ms in WT [n=7] and 55.1±1.3 ms in [n=7];P<0.01). These data represent the first direct demonstration of conduction defects in the specialized conduction system of Cx40–/–mice and provide new insight into the role of gap junctions in cardiac impulse propagation.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

We recently reported that leukemia inhibitory factor (LIF) enhances Ca2+]ithrough an increase in L-type Ca2+current (ICa,L) in adult cardiomyocytes. The aim of this study was to investigate whether LIF activates Ca2+-dependent signaling molecules, such as calcineurin and calmodulin kinases II and IV (CaMKII and CaMKIV), and, if so, whether these Ca2+-mediated signaling events contribute to LIF-mediated cardiac hypertrophy. We first confirmed that LIF increasedICa,Land [Ca2+]iin primary cultured rat neonatal cardiomyocytes. Calcineurin, CaMKII, and CaMKIV activities increased at 2 minutes and peaked by 1.6-, 2.2-, and 2.2-fold, respectively, at 15 minutes. Nicardipine or verapamil fully inhibited these activities. Autophosphorylation of CaMKII was also observed to parallel the timing of CaMKII activity, and this phosphorylation was blocked by nicardipine, verapamil, or EGTA. LIF treatment led to a 3-fold increase in nuclear factor of activated T cell–luciferase activity. To confirm that inositol triphosphate (IP3)-induced Ca2+release from sarcoplasmic reticulum was not involved in this process, IP3content and phosphorylation of phospholipase C&ggr; were investigated. LIF did not increase IP3content or phosphorylate phospholipase C&ggr;. KN62 (an inhibitor of CaMKII and CaMKIV) attenuated c-fos, brain natriuretic peptide, &agr;-skeletal actin, and atrial natriuretic peptide expression. KN62 suppressed the LIF-induced increase in [3H]phenylalanine uptake and cell size. Cyclosporin A and FK506 slightly attenuated brain natriuretic peptide but did not affect c-fos or atrial natriuretic peptide expression. Cyclosporin A significantly reduced the LIF-induced increase in [3H]phenylalanine uptake. These findings indicated that LIF activated CaMKII, CaMKIV, and calcineurin through an increase inICa,Land [Ca2+]iand that CaMKII, CaMKIV, and calcineurin are critically involved in LIF-induced cardiac hypertrophy.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Maternal hypercholesterolemia during pregnancy is associated with a marked increase in aortic fatty streak formation in human fetuses and faster progression of atherosclerosis during normocholesterolemic childhood. However, the mechanisms responsible are unknown, and the contribution of genetic differences is difficult to assess in humans. The goal of this study was to determine whether maternal hypercholesterolemia per se may cause enhanced fatty streak formation in offspring and whether interventions during pregnancy can reduce it. During pregnancy, 1 group of New Zealand White rabbits was fed control chow and 8 groups were fed hypercholesterolemic diets Chol 1 (yielding plasma cholesterol of 153 mg/dL) or Chol 2 (yielding 359 mg/dL) without or with cholestyramine, vitamin E, or both. Offspring (n=15 to 25 per group) were killed at birth. Maternal hypercholesterolemia enhanced mean lesion size in the aorta of their offspring at birth from 44±18×103&mgr;m2per section in controls to 85±26×103in Chol 1 and 156±49×103in Chol 2 groups (P<0.0001 for both). Cholestyramine or vitamin E treatment of mothers significantly reduced atherosclerosis at birth by up to 39% compared with controls on the same diet. Oxidized fatty acids and malondialdehyde in aortic atherosclerotic lesions and plasma were similarly affected by diets and treatment as atherosclerosis. Our results establish the causal role of hypercholesterolemia and peroxidation in fetal atherogenesis and demonstrate that both lipid-lowering and antioxidant interventions during pregnancy can reduce it. If it can be established that interventions in mothers also affect progression of lesions after birth, this may indicate a novel approach for the prevention of atherosclerosis.

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