Spontaneous activity in transgenic mouse heart: comparison of primary atrial tumor with cultured AT-1 atrial myocytes.

Introduction: We have generated transgenic animals that heritably develop atrial tumors composed of differentiated proliferating cardiomyocytes. Experiments were initiated to characterize the electrical properties of these cells.

Methods And Results: We show that the primary atrial tumors are composed of discrete foci that exhibit spontaneous automatic activity.

Time course of changes in intracellular K+, Na+, and pH of subendocardial Purkinje cells during the first 24 hours after coronary occlusion.

We investigated the basis for the alterations in the intracellular potassium and sodium activity occurring in subendocardial Purkinje fibers surviving in 24-hour infarcts by examining ion activities in these Purkinje fibers removed from infarcting hearts at earlier times. Specifically, we examined intracellular potassium activity, sodium activity, and pH at 1 and 3 hours after ligation of the left anterior descending coronary artery, and we correlated the changes in ion activity with changes in maximum diastolic potential. We tested various mechanistic hypotheses relating to how the ion activity changes develop and how they affect membrane potential.

Postischaemic reperfusion injury in the isolated rat heart: effect of ruthenium red.

Study Objective: The aim was to investigate the effect of attenuating mitochondrial calcium uptake with ruthenium red on myocardial function and the resultant necrosis following prolonged ischaemia and reperfusion in isolated rat hearts. Mitochondrial dysfunction, secondary to increased calcium uptake, has been implicated as an important mediator of reperfusion injury in the heart.

Design: To examine the role of mitochondrial calcium uptake in mediating ischaemic and reperfusion injury, isolated rat hearts were perfused with ruthenium red (n = 6), a polysaccharide dye which inhibits calcium uptake by mitochondria, and were compared to control perfused hearts (n = 7).

Proliferation in vivo and in culture of differentiated adult atrial cardiomyocytes from transgenic mice.

Transgenic mice expressing atrial natriuretic factor-SV40 T-antigen fusion genes (ANF-TAG) developed unilateral right atrial tumors composed of differentiated dividing cardiomyocytes. The atrial tumors could be propagated as transplantable tumor lineages in syngeneic animals. Cardiomyocytes derived from ANF-TAG atrial tumors did not proliferate in tissue culture.

Electrogenic Na(+)-K+ pump in Purkinje myocytes isolated from control noninfarcted and infarcted hearts.

We combined a method of Na+ loading (zero K+ exposure) with voltage-clamp techniques to determine whether malfunctioning of the Na(+)-K+ pump underlies the abnormalities in the resting potential and the repolarization process observed in subendocardial Purkinje cells dispersed from the canine infarcted ventricle (IZPCs) 24 h after coronary artery occlusion. Stimulation of the transient outward current (ipump) was produced by a 3-min exposure to zero K+ and then reexposure to 4 mM K+ Tyrode solution. We compared the properties of ipump in IZPCs to ipump in Purkinje cells dispersed from fiber strands (SPCs) or from the subendocardium of the normal hearts (NZPCs).