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Harold V M van Rijen

Publications and source records attributed to Harold V M van Rijen.

14 recordsLinked to original sources
PubMed2006

Cardiomyocyte-restricted deletion of connexin43 during mouse development.

Although the gap junction protein Connexin43 (Cx43) is expressed in various cell types during embryonic development, mice with a global inactivation of Cx43 survive until birth but die perinatally due to an obstruction of the right ventricular outflow tract of the heart. To analyze the functional role of Cx43 gap junction channels in cardiomyocytes of the developing and early postnatal heart, we used alphaMyHC-Cre mice to ablate Cx43 expression selectively in cardiomyocytes during development. We found efficient ablation of Cx43 in cardiomyocytes during embryonic development starting at embryonic day (ED) 9.5 in the ventricular wall. Analyses of cardiac Cx43 protein at birth indicated complete loss of Cx43 expression in cardiomyocytes. All mice homozygously deficient for Cx43 in cardiomyocytes died until postnatal day (PD) 16. Heterozygous inactivation of Cx43 in cardiomyocytes neither altered atrial nor ventricular activation, but homozygous ablation led to changes in ventricular activation, i.e. significant decrease of the QRS-amplitude and prolonged QRS-duration already at PD 4. Cardiac morphology was similar to controls until PD 1, but subtle morphological changes were found in a subgroup of mutant mice at later stages. Besides narrowing of the ventricular outlet region at PD 6, hypertrophy of ventricular myocardium was found at PD 12. Our data indicate that complete inactivation of cardiac Cx43 during development predisposes hearts to develop postnatal morphological alterations, which differ from outflow tract obstructions described for Cx43 null mice. In addition, complete loss of cardiac Cx43 protein during development correlates with slowed ventricular activation at PD 4, impairs viability during development, and leads to death of all mutant mice until PD 16.

Age Factors↗
PubMed2006

Cardiac morphogenetic defects and conduction abnormalities in mice homozygously deficient for connexin40 and heterozygously deficient for connexin45.

Connexin40 (Cx40) and connexin45 (Cx45) are involved in both cardiac morphogenesis and propagation of electrical activity. We found that Cx40/Cx45 double deficiency (Cx40(-/-)/Cx45(+/-)) causes a variety of cardiac defects leading to high mortality during embryonic development and at birth. The majority of Cx40(-/-)/Cx45(+/-) embryos and postnatal mice suffered from atrioventricular septal defects. Additional cardiac abnormalities, e.g., ventricular septal defects and abnormal myocardial arrangement, occurred at lower abundance. Electrocardiograms of Cx40(-/-)/Cx45(+/+) and Cx40(-/-)/Cx45(+/-) mice revealed prolongation of P-wave, PQ interval and QRS duration compared to controls. Interestingly, in Cx40(-/-)/Cx45(+/-) mice, PQ interval and QRS duration were significantly prolonged compared to Cx40(-/-)/Cx45(+/+) mice. We conclude that the gap junctional proteins Cx40 and Cx45 have overlapping and partially compensatory functions with regard to heart morphogenesis and cardiac conduction. Cx45 might be one of the genetic modifiers that can cause variations in the phenotype of connexin40-deficient animals. Our findings may be particularly relevant for understanding molecular factors contributing to human congenital cardiac diseases.

Animals↗
PubMed2006

Age and gender related reference values for transthoracic Doppler-echocardiography in the anesthetized CD1 mouse.

OBJECTIVE: Doppler-echocardiography of the mouse has evolved to a commonly used technique in the past years as recent advances in imaging quality have substantially improved spatial and temporal resolution allowing the adaptation of this technique to murine models. Although mouse echocardiography is widely used, there is only little information on reference data for wild-type animals available, particularly in older mice. METHODS: We therefore established a database with echocardiographic reference-values in a large set of young (8 weeks) and older adult (52 weeks) Swiss type CD1-mice of either sex. We performed a complete Doppler-echocardiographic examination under light Ketamine-Xylazine-anesthesia. LV-mass was calculated and compared with necropsy heart weights to validate the LV-mass calculation. RESULTS: Doppler-echocardiographic measurements in mice were feasible to assess cardiac morphology and function. Sonomorphological and functional parameters hardly changed between the age of 12 and 52 weeks. Wall thickness, LV-mass and cardiac output were stable with aging. There was a good relative correlation between echocardiographically estimated LV-mass and necropsy heart weight although absolute values differed. There were no significant echocardiographic differences between male and female mice. CONCLUSIONS: The reference values established in this study can be useful in recording and quantifying pathological changes in murine models of cardiovascular diseases. There is hardly any change of cardiac function between the age of 12 and 52 weeks.

Age Factors↗
PubMed2006

Physiology of cardiovascular gap junctions.

Cardiac gap junction channels are crucial for conduction of the electric impulse. Between cardiomyocytes there exist gap junctions constructed from connexin40 (Cx40), Cx43 and Cx45. A fourth isoform, Cx37, is expressed in the endothelial lining. Each of these channel types possesses specific properties and their functioning is regulated by various mechanisms. In this chapter we compare the physiological differences between these channels and discuss the factors involved in modulation of channel properties. Next, we evaluate how alterations in expression and differential regulation of channel properties affect cardiac impulse propagation.

Animals↗
PubMed2006

Connexins and cardiac arrhythmias.

During cardiac remodeling, impulse conduction in the heart is altered by changes in excitability, electrical coupling, and tissue architecture. The impairment of normal impulse conduction is one of the factors that increases the propensity for arrhythmias. This chapter focuses on the relationship between electrical coupling between ventricular myocytes and arrhythmogenesis. Mouse models of decreased electrical coupling in the heart have shown that a clinically relevant 50% reduction in gap junctions in the heart has no effect on impulse conduction or arrhythmogenesis. To impair conduction and arrhythmias, coupling has to be reduced to very low levels. Apparently, there is a large conduction reserve, which can preserve normal impulse conduction even when electrical coupling is moderately reduced. However, cardiac remodeling is also associated with reduced excitability and increased levels of collagen deposition (fibrosis). It is therefore presumably the combination of, in itself ineffective, reduction of electrical coupling with other impairments like fibrosis or reduced excitability that causes the limits of conduction reserve to be exceeded, thereby resulting in abnormal impulse conduction and enhanced arrhythmogenesis.

Animals↗
PubMed2005

Discontinuous conduction in mouse bundle branches is caused by bundle-branch architecture.

BACKGROUND: Recordings of the electrical activity of mouse bundle branches (BBs) suggest reduced conduction velocity (CV) in the midseptal compared with the proximal part of the BB. The present study was performed to elucidate the mechanism responsible for this slowing of conduction. METHODS AND RESULTS: Hearts of 16 mice were isolated and Langendorff perfused. After the right and left ventricular free walls were removed, the extracellular activity of the BB was mapped with a 247-point electrode. Premature stimulation was used to estimate CV restitution in the BBs. Expression/distribution of connexin40 (Cx40), Cx43, and Cx45 was determined. Morphology of the conduction system was assessed by whole-mount acetylcholine esterase staining and in Cx40(+/KI-GFP) hearts. Effective CV in the midseptal part of the left and right BBs was reduced by 50% compared with the proximal BB. CV restitution in the proximal and midseptal parts of the BBs was similar. Myocytes labeled positive for Cx40 and Cx45 in the entire BB. Cx43 colocalized with Cx40 and Cx45 only in the very distal BB. Subcellular distribution of gap junctions differed between proximal and distal BBs. Geometry of the midseptal and distal BBs revealed on both sides a profuse network of interlacing fibers, whereas the proximal BB consisted of a single (right BB) or multiple (left BB) parallel fibers. CONCLUSIONS: Comparison of connexin expression/distribution, geometry of the BBs, and CV characteristics suggests that increased path length for activation resulting from BB geometry is responsible for the apparently reduced CV in the midseptal BB of the mouse heart.

Animals↗
PubMed2005

Impaired impulse propagation in Scn5a-knockout mice: combined contribution of excitability, connexin expression, and tissue architecture in relation to aging.

BACKGROUND: The SCN5A sodium channel is a major determinant for cardiac impulse propagation. We used epicardial mapping of the atria, ventricles, and septae to investigate conduction velocity (CV) in Scn5a heterozygous young and old mice. METHODS AND RESULTS: Mice were divided into 4 groups: (1) young (3 to 4 months) wild-type littermates (WT); (2) young heterozygous Scn5a-knockout mice (HZ); (3) old (12 to 17 months) WT; and (4) old HZ. In young HZ hearts, CV in the right but not the left ventricle was reduced in agreement with a rightward rotation in the QRS axes; fibrosis was virtually absent in both ventricles, and the pattern of connexin43 (Cx43) expression was similar to that of WT mice. In old WT animals, the right ventricle transversal CV was slightly reduced and was associated with interstitial fibrosis. In old HZ hearts, right and left ventricle CVs were severely reduced both in the transversal and longitudinal direction; multiple areas of severe reactive fibrosis invaded the myocardium, accompanied by markedly altered Cx43 expression. The right and left bundle-branch CVs were comparable to those of WT animals. The atria showed only mild fibrosis, with heterogeneously disturbed Cx40 and Cx43 expression. CONCLUSIONS: A 50% reduction in Scn5a expression alone or age-related interstitial fibrosis only slightly affects conduction. In aged HZ mice, reduced Scn5a expression is accompanied by the presence of reactive fibrosis and disarrangement of gap junctions, which results in profound conduction impairment.

Aging↗
PubMed2005

Mouse model of SCN5A-linked hereditary Lenègre's disease: age-related conduction slowing and myocardial fibrosis.

BACKGROUND: We have previously linked hereditary progressive cardiac conduction defect (hereditary Lenègre's disease) to a loss-of-function mutation in the gene encoding the main cardiac Na+ channel, SCN5A. In the present study, we investigated heterozygous Scn5a-knockout mice (Scn5a+/- mice) as a model for hereditary Lenègre's disease. METHODS AND RESULTS: In Scn5a+/- mice, surface ECG recordings showed age-related lengthening of the P-wave and PR- and QRS-interval duration, coinciding with previous observations in patients with Lenègre's disease. Old but not young Scn5a+/- mice showed extensive fibrosis of their ventricular myocardium, a feature not seen in wild-type animals. In old Scn5a+/- mice, fibrosis was accompanied by heterogeneous expression of connexin 43 and upregulation of hypertrophic markers, including beta-MHC and skeletal alpha-actin. Global connexin 43 expression as assessed with Western blots was similar to wild-type mice. Decreased connexin 40 expression was seen in the atria. Using pangenomic microarrays and real-time PCR, we identified in Scn5a+/- mice an age-related upregulation of genes encoding Atf3 and Egr1 transcription factors. Echocardiography and hemodynamic investigations demonstrated conserved cardiac function with aging and lack of ventricular hypertrophy. CONCLUSIONS: We conclude that Scn5a+/- mice convincingly recapitulate the Lenègre's disease phenotype, including progressive impairment with aging of atrial and ventricular conduction associated with myocardial rearrangements and fibrosis. Our work provides the first demonstration that a monogenic ion channel defect can progressively lead to myocardial structural anomalies.

Age Factors↗
PubMed2004

Architectural and functional asymmetry of the His-Purkinje system of the murine heart.

OBJECTIVE: The aim of this work was to target a vital reporter gene in the mouse cardiac conduction system (CS) to distinguish this tissue from the surrounding myocardium in the adult heart. METHODS: A transgenic mouse line has been created in which EGFP is expressed under the control of the Cx40 gene. Correlative investigations associating EGFP imaging and electrophysiological techniques were carried out on the adult heart and isolated cardiomyocytes. RESULTS: In the heart of the Cx40(EGFP/+) mice, EGFP signal was seen in the coronary arteries, the atria, the atrioventricular (AV) node and the His-Purkinje system. The latter was found to be structurally and functionally asymmetrical. The anatomical asymmetry was apparent in both the number of strands or fasciculi making up the His bundle branches (BBs) (1 strand on the right, 20 or so on the left), and the density (low on the right, high on the left) of the network of Purkinje fibers (PFs) that extends over the ventricular wall surfaces. The profiles of the electrical activation patterns recorded on the right and left flanks of the septum were also asymmetrical, mirroring the architecture of the branches. EGFP made it easy to identify the Purkinje cells in populations of dissociated cardiomyocytes and they were investigated using the patch-clamp technique. The hyperpolarization-activated current (If) was recorded in all spontaneously active Purkinje cells. CONCLUSIONS: This investigation provides positive evidence of the asymmetry of the His-Purkinje system of the adult mouse, and the first patch-clamp recording data on murine cardiac Purkinje cells. This mouse model opens up new perspectives for investigating the contribution of specific genes to the morphology and function of the His-Purkinje system.

Action Potentials↗
PubMed2004

Slow conduction and enhanced anisotropy increase the propensity for ventricular tachyarrhythmias in adult mice with induced deletion of connexin43.

BACKGROUND: Connexin 43 (Cx43) is a major determinant of conduction in the ventricular working myocardium of mammals. We investigated the effect of decreased Cx43 expression on conduction velocity and arrhythmogenesis using adult mice with inducible deletion of Cx43. METHODS AND RESULTS: Cx43Cre-ER(T)/+ mice, in which 1 coding region of the Cx43 gene was replaced by Cre-ER(T), were mated to Cx43fl/fl mice, generating Cx43Cre-ER(T)/fl mice. Application of 4-hydroxytamoxifen (4-OHT) induced Cre-ER(T)-mediated deletion of the floxed Cx43 allele. Epicardial ventricular mapping using a 13x19 multiterminal electrode grid (300-microm spacing) was performed on Langendorff-perfused hearts from Cx43fl/fl plus carrier (n=10), Cx43fl/fl plus 4-OHT (n=10), Cx43 Cre-ER(T)/fl plus carrier (n=9), and Cx43Cre-ER(T)/fl plus 4-OHT (n=10). Cx43 protein amount in group 3 hearts was decreased by 50% compared with group 1. 4-OHT did not affect cardiac protein amounts in group 2 but decreased Cx43 expression up to 95% in group 4 compared with group 3. Epicardial activation of both left ventricle (LV) and right ventricle (RV) during sinus rhythm was similar in all groups. Conduction velocity (CV) changed only in group 4 animals. For RV (LV), longitudinal CV decreased from 38 (35) to 31.6 (33.6) and transverse CV from 24.4 (16.8) to 10.1 (11.3) cm/s. Dispersion of conduction in RV (LV) was increased by 91% (38%). Programmed stimulation resulted in ventricular arrhythmias in group 4 (7 of 10 mice) but never in groups 1 through 3. CONCLUSIONS: Heterozygous expression of Cx43 did not affect ventricular conduction velocity. Up to 95% decrease of Cx43 protein in 4-OHT-treated Cx43(Cre-ER(T)/fl) mice reduced conduction velocity and increased dispersion of conduction and propensity for ventricular arrhythmias.

Animals↗
PubMed2003

Tissue discontinuities affect conduction velocity restitution: a mechanism by which structural barriers may promote wave break.

BACKGROUND: The mechanism by which structural barriers promote wave break and fibrillation is unclear. Conduction velocity (CV) restitution is an important determinant of wave break. Abnormal CV restitution is associated with ventricular fibrillation in patients with heart disease and arises preferentially in fibrotic myocardium. We hypothesize that tissue discontinuities imposed by structural barriers cause abnormal CV restitution. METHODS AND RESULTS: Tissue discontinuities were simulated in cultures of neonatal rat heart cells grown in 8-armed star patterns. Premature stimulation was applied at the extremity of 1 arm (n=12) while extracellular electrograms were recorded at 24 sites throughout the star. Action potentials were recorded at the following 3 sites: in the stimulated arm and at the discontinuity both proximal to and distal from the star center. Extracellular recordings revealed progressive increases in activation delay (indicative for abnormal CV restitution) only at the discontinuity from arms proximal to the star center. The mean increase in delay was 0.81+/-0.41 ms/10 ms for recording sites proximal to and 3.13+/-0.58 ms/10 ms for sites distal from this discontinuity. Depolarizing currents were determined in single cells during premature stimulation and for voltage configurations similar to those arising at the discontinuity. Both voltage-clamp measurements and computer simulations showed that delay at the discontinuity was associated with biphasic, prolonged activation and delayed inactivation of depolarizing current. CONCLUSIONS: Tissue discontinuities cause abnormal CV restitution. Rapid increase in activation after an initial slow activation and delayed inactivation at the discontinuity lengthen the duration of depolarizing current and cause the abnormal restitution.

Action Potentials↗
PubMed2002

Remodeling of gap junctions in mouse hearts hypertrophied by forced retinoic acid signaling.

BACKGROUND: Beta-MHC-hRARalpha transgenic mice express a constitutively active (truncated) form of the human retinoic acid receptor which triggers development of dilated cardiomyopathy. In those hearts, we studied expression of gap junction proteins in relation to electrical impulse propagation. METHODS AND RESULTS: As compared to wildtype mice, hearts of 4-6 month old mice with 7-12 inserted hRARalpha copies are marked by an increased heart weight/body weight- and heart weight/tibia length ratio. 3-extremity lead ECGs revealed prolongation of the Q-j interval suggesting delayed ventricular activation. Mapping of electrical activity of epi- and endocardial left ventricular free wall revealed activation delay, increased heterogeneity in conduction and regional conduction block. Ventricular tachycardias did not occur spontaneously nor could be induced by ventricular pacing. Immunohistochemical analysis showed profound and heterogeneous redistribution and down-regulation of the gap junction protein connexin43 (Cx43) in the left ventricular free wall. Here, hRARalpha expression induced re-expression of the hypertrophic markers alpha-skeletal actin and beta-MHC, and in 3 out of 10 severely affected mice, re-expression of Cx40. Concomitant with changes in expression/distribution of Cx43, changes in expression and distribution of beta-catenin and N-cadherin (two other intercalated disk associated proteins) were observed. CONCLUSIONS: Beta-MHC-hRARalpha transgenic hearts show heterogeneous re-expression of (early) sarcomeric genes while expression of connexin43, N-cadherin and beta-catenin is down-regulated. We postulate that the resulting aberrant ventricular activation does not trigger development of lethal arrhythmias due to the small size of remaining healthy ventricular tissue where the transgene is not expressed.

Actins↗