Di(2-ethylhexyl) phthalate (DEHP) is a widely used plasticizer found in a variety of polyvinyl chloride (PVC) medical products. The results of studies in experimental animals suggest that DEHP leached from flexible PVC tubing may cause health problems in some patient populations. While the cancerogenic and reproductive effects of DEHP are well recognized, little is known about the potential adverse impact of phthalates on the heart. This study examined the effects of clinically relevant concentrations of DEHP on neonatal rat cardiomyocytes. It was found that application of DEHP to a confluent, synchronously beating cardiac cell network, leads to a marked, concentrationdependent decrease in conduction velocity and asynchronous cell beating. The mechanism behind these changes was a loss of gap junctional connexin-43, documented using western blot analysis, dye-transfer assay and immunofluorescence. In addition to its effect on electrical coupling, DEHP treatment also affected the mechanical movement of myocyte layers. The latter was linked to the decreased stiffness of the underlying fibroblasts, as the amount of triton-insoluble vimentin was significantly decreased in DEHP-treated samples. The data indicate that DEHP, in clinically relevant concentrations, can impair the electrical and mechanical behavior of a cardiac cell network. Applicability of these findings to human patients remains to be established.

treated for 10 min with no drug (control) or with the I NaL inhibitors ranolazine (Ran; 3, 10 mM) or tetrodotoxin (TTX, 1 mM), then additionally exposed for 60 min to ouabain (1.3 mM in 23 Na-and 0.75 mM in 31 P-NMR experiments), after which all drugs were washed out for 20 min. Na þ i was not changed by TTX or Ran alone. However, Ran (10 mM) and TTX significantly attenuated effects of ouabain to increase Na þ i and decrease DG ~ATP (see Figure ). The findings suggest that I NaL contributes significantly to Na þ i accumulation during exposure of myocytes to cardiac glycosides.

We report a simple in vitro model of cardiac tissue that mimics three-dimensional (3-D) environment and mechanical load conditions and, as such, may serve as a convenient method to study stem cell engraftment or address developmental questions such as cytoskeleton or intercalated disk maturation. To create in vitro cardiac fibers we used Matrigel, a commercially available basement membrane preparation. A semisolid pillow from concentrated Matrigel was overlaid with a suspension of rat neonatal cardiomyocytes in a diluted Matrigel solution. This created an environment in which the multicellular fibers continuously contracted against a mechanical load. The described approach allows continuous structural and functional monitoring of 20-300-micron-thick cardiac fibers and provides easy access to epitopes for immunostaining purposes.

Constitutive overexpression of N-cadherin in mouse embryonic stem cells led to marked changes in the phenotype and adhesion properties of these cells. The changes included the formation of smaller embryonic bodies, elevated mRNA and total protein levels of N-cadherin, and increased amounts of p120 catenin and connexin-43. N-cadherin cells exhibited decreased attachment to non-cell surfaces, while their adhesiveness to each other and to rat neonatal cardiomyocytes was significantly elevated. The findings suggest that N-cadherin overexpression can facilitate electromechanical integration of stem cells into excitable tissues with endogenously high levels of N-cadherin, such as the heart and brain.

Cell-transplantation therapy is a promising treatment option that is being actively explored as a way to repair cardiac muscle. The ultimate goal is to reconstitute the architecture of the cardiac muscle and to reestablish electrical propagation, while avoiding hypertrophy and scar formation. In this review, we focus on recent advances in the field as well as the difficulties encountered when the engraftment of cells into the host tissue is to be confirmed and functionally characterized. This is critical since incomplete or partial engraftment of transplanted cells within the host cardiac network exacerbates the heterogeneity already present in the injured myocardium and increases its propensity to arrhythmia. We conclude with a brief discussion of how the modulation of cell adhesion via modification of coupling proteins within transplanted cells may facilitate engraftment and alleviate the arrhythmogenic potential of cardiac grafts.

Pluripotent embryonic stem cells (ESC) are a promising source for the regeneration of damaged tissues. To date, it is not known whether genetic modification of ESC can promote their integration into the host tissue and whether upregulation of the adhesion proteins would facilitate this process. We tested a hypothesis that overexpression of a major adhesion protein, N‐Cadherin, will alter the adhesive properties of embryonic stem cells. Constitutive overexpression of a major adhesion protein, N‐Cadherin, in an embryonic stem cell line led to marked changes in the phenotype and adhesion properties of these cells. These changes occur despite the lack of a detectable increase in membrane‐associated N‐Cadherin. The level and the membrane distribution of gap junctional protein Connexin‐43 and the amount of p120‐catenin are elevated in N‐Cadherin overexpressing cells, pointing to altered protein‐protein interactions at cell junctions. The data suggest that while the overexpression of N‐Cadherin makes embryonic stem cells more adhesive, the effect might be paradoxically mediated by other proteins. Financial support by the American Heart Association, MidAtlantic Affiliate (0715335U) and the NIH (HL076722, HL087529) is gratefully acknowledged.

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Di(2‐ethylhexyl) phthalate (DEHP) is a widely used plasticizer that is found in a variety of polyvinyl chloride (PVC) medical products. DEHP leaches from PVC tubing and has been linked to cancerogenic and adverse reproductive effects. Currently, little is known of the impact of phthalates on the heart. The effects of DEHP were examined by conducting in vitro experiments using confluent layers of neonatal cardiomyocytes. Exposure to 50ug/mL DEHP for 72‐hours led to a decrease in conduction velocity and asynchronous contractions. These effects were caused by a decrease in the presence of gap junctional connexin‐43 expression. DEHP treatment also affected the mechanical properties of the myocyte network, leading to an unusual type of cell motion. These findings were not attributed to modifications in cell‐cell adhesion, as changes in adherens junction and focal adhesion proteins were not significantly altered by DEHP treatment. Instead, the modified motion and was linked to changes within the underlying fibroblasts. The latter expressed significantly less triton‐insoluble vimentin, compared to control samples. Applicability of these findings to human patients remains to be established. Financial support by the American Heart Association, MidAtlantic Affiliate (0715335U) and the NIH (HL076722, HL087529) is gratefully acknowledged.