The electrical activity of embryonic chick heart cells isolated in tissue culture singly or in interconnected cell sheets

Cell chirality in cardiovascular development and disease

The cardiovascular system demonstrates left-right (LR) asymmetry: most notably, the LR asymmetric looping of the bilaterally symmetric linear heart tube. Similarly, the orientation of the aortic arch is asymmetric as well. Perturbations to the asymmetry have been associated with several congenital heart malformations and vascular disorders. The source of the asymmetry, however, is not clear. Cell chirality, a recently discovered and intrinsic LR asymmetric cellular morphological property, has been implicated in the heart looping and vascular barrier function. In this paper, we summarize recent advances in the field of cell chirality and describe various approaches developed for studying cell chirality at multi- and single-cell levels. We also examine research progress in asymmetric cardiovascular development and associated malformations. Finally, we review evidence connecting cell chirality to cardiac looping and vascular permeability and provide thoughts on future research directions for cell chirality in the context of cardiovascular development and disease.

Multicellular In vitro Models of Cardiac Arrhythmias: Focus on Atrial Fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice with a large socioeconomic impact due to its associated morbidity, mortality, reduction in quality of life and health care costs. Currently, antiarrhythmic drug therapy is the first line of treatment for most symptomatic AF patients, despite its limited efficacy, the risk of inducing potentially life-threating ventricular tachyarrhythmias as well as other side effects. Alternative, in-hospital treatment modalities consisting of electrical cardioversion and invasive catheter ablation improve patients' symptoms, but often have to be repeated and are still associated with serious complications and only suitable for specific subgroups of AF patients. The development and progression of AF generally results from the interplay of multiple disease pathways and is accompanied by structural and functional (e.g., electrical) tissue remodeling. Rational development of novel treatment modalities for AF, with its many different etiologies, requires a comprehensive insight into the complex pathophysiological mechanisms. Monolayers of atrial cells represent a simplified surrogate of atrial tissue well-suited to investigate atrial arrhythmia mechanisms, since they can easily be used in a standardized, systematic and controllable manner to study the role of specific pathways and processes in the genesis, perpetuation and termination of atrial arrhythmias. In this review, we provide an overview of the currently available two- and three-dimensional multicellular in vitro systems for investigating the initiation, maintenance and termination of atrial arrhythmias and AF. This encompasses cultures of primary (animal-derived) atrial cardiomyocytes (CMs), pluripotent stem cell-derived atrial-like CMs and (conditionally) immortalized atrial CMs. The strengths and weaknesses of each of these model systems for studying atrial arrhythmias will be discussed as well as their implications for future studies.

Intrinsic cellular chirality regulates left-right symmetry breaking during cardiac looping

Cell chirality, or handedness of the cell, is a newly discovered, fundamental property of the cell, so far studied in cell culture only with micropatterning or graded biomaterial-based approaches. The relevance of intrinsic cell chirality on organ laterality is yet to be established. Cardiac looping is the first organ-specific left–right asymmetry evident during embryogenesis. Despite extensive insights into the molecular signals regulating cardiac left–right asymmetry, the biophysical mechanism is still unknown. Our findings establish intrinsic cell chirality as a regulator of cardiac laterality. This study combines an in vitro chirality assay with embryonic left–right asymmetry in vivo and will significantly impact the understanding and future studies of embryonic left–right asymmetry and congenital heart diseases.

The vertebrate body plan is overall symmetrical but left–right (LR) asymmetric in the shape and positioning of internal organs. Although several theories have been proposed, the biophysical mechanisms underlying LR asymmetry are still unclear, especially the role of cell chirality, the LR asymmetry at the cellular level, on organ asymmetry. Here with developing chicken embryos, we examine whether intrinsic cell chirality or handedness regulates cardiac C looping. Using a recently established biomaterial-based 3D culture platform, we demonstrate that chick cardiac cells before and during C looping are intrinsically chiral and exhibit dominant clockwise rotation in vitro. We further show that cells in the developing myocardium are chiral as evident by a rightward bias of cell alignment and a rightward polarization of the Golgi complex, correlating with the direction of cardiac tube rotation. In addition, there is an LR polarized distribution of N-cadherin and myosin II in the myocardium before the onset of cardiac looping. More interestingly, the reversal of cell chirality via activation of the protein kinase C signaling pathway reverses the directionality of cardiac looping, accompanied by a reversal in cellular biases on the cardiac tube. Our results suggest that myocardial cell chirality regulates cellular LR symmetry breaking in the heart tube and the resultant directionality of cardiac looping. Our study provides evidence of an intrinsic cellular chiral bias leading to LR symmetry breaking during directional tissue rotation in vertebrate development.

A video-computer for the chronotropic and inotropic measurements of the beating of cultured heart cells

A video-computer system has been developed to measure the chronotropy and inotropy of cultured heart cells. The motion of the cell is followed by recording of the changes of light intensity from the edge of a beating cell. With this system the velocity of contraction and relaxation, the time to peak contraction, relaxation time and the displacement of the cell in culture can be measured for the first time. Also, the rate of beating can be measured beyond the limits set by visual counting. With the application of this technique to the cultured heart cell system we have found that norepinephrine increases the velocity of relaxation thus reducing the ratio of contraction velocity to relaxation velocity, and reduces the twitch time. Increased external calcium, on the other hand, has little effect on either the velocity of contraction or relaxation but, like norepinephrine, decreases the twitch time.

Excitation-contraction coupling of isolated cardiac fibers with disrupted or closed sarcolemmas. Calcium-dependent cyclic and tonic contractions

Single cells of adult rat ventricle were separated with 0.1% trypsin and 0.05-0.1% collagenase. Ten percent of these cells were tubular and striated, contracted spontaneously in the presence of 0.05 mM CaCl 2 or after addition of 0.1-0.5 mM CaCl 2 , and developed contracture in 1 mM CaCl 2 . A resting potential of -30 to -50 mv and an action potential more than 100 msec in duration were recorded in some of the cells. These relatively intact cells were contrasted with myocardial fibers (10-100 µ ) obtained by homogenization. In the presence of 0.025 mM ethyleneglycol bis(β-aminoethylether)-N, N'-tetraacetic acid (EGTA), localized cyclic contractions with intracellular asynchrony were observed under the phase microscope in obviously disrupted areas of these mechanically separated fibers. These contractions were insensitive to the ratio of Na + to K + , and neither resting potentials nor action potentials were observed. Thus, these disrupted fibers were considered skinned fibers of cardiac muscle; this assumption was further supported by the absence of modification of fiber sensitivity to Ca 2+ by simultaneous skinning with EDTA. Effects of Ca 2+ were studied with control of pCa in the medium by EGTA-Ca buffers, either directly on the homogenate or after depletion of Ca 2+ content of the tissue. At 22°C, pH 7.0, and in the presence of 4 mM MgCl 2 , 5 mM adenosine triphosphate, and 2 mM EGTA, cyclic contractions were inhibited and a tonic contraction was induced at a pCa of 6.25-6.5, which represented the threshold for activation of myofilaments. With the same medium but with low EGTA (less than 0.2 mM), cyclic contractions were obtained if pCa was equal to or lower than 7.4-7.6. Therefore, these contractions corresponded to a cyclic release of Ca 2+ from cellular stores, yielding a transient activation of myofilaments. This large release of Ca 2+ within the fiber was induced by a small addition of Ca 2+ to the medium. It was concluded that a regenerative release of Ca 2+ could be demonstrated in heart muscle under these conditions. Localized cyclic contractions were not observed in disrupted fibers of frog heart, in which spontaneously beating cells could be separated with enzymes.

Synthetic strands of cardiac muscle: growth and physiological implication

Cardiac muscle cells obtained fronm disaggregated embryonic chick hearts were cultured on difjerentially treated oriented substrata. Subsequent cell reaggregation, growth, and attachmwent produced linearly organized strands of cardiac muscle with dimensions suitable for electrophysiological analysis. Along the strand, areas that contained few muscle cells demonstrated reduced conduction velocity and were subject to propagation failure.