Synchronous progression of calcium transient-dependent beating and sarcomere destruction in apoptotic adult cardiomyocytes

Abstract

2ϩ transients in initiation of apoptotic processes in this cell type. Simultaneously with the beating, these cells show dynamic structural alteration resulting from cytoskeletal disintegration that is quite rapid. Because of the specialized structure and extensive cytoskeleton of cardiomyocytes, we hypothesized that its degradation in so short a time would require a particularly efficient mechanism. To better understand this mechanism, we used serial video microscopy to observe ␤-adrenergic stimulation-induced apoptosis in isolated adult rat cardiomyocytes while simultaneously recording intracellular Ca 2ϩ concentration and cell length. Trains of Ca 2ϩ transients and corresponding rhythmic contractions and relaxations (beating) were observed in apoptotic cells. Frequencies of Ca 2ϩ transients and beating gradually increased with time and were accompanied by cellular shrinkage. As the cells shrank, amplitudes of Ca 2ϩ transients declined and diastolic intracellular Ca 2ϩ concentration increased until the transients were lost. Beating and progression of apoptosis were significantly inhibited by antagonists against the L-type Ca 2ϩ channel (nifedipine), ryanodine receptor (ryanodine), inositol 1,4,5-trisphosphate receptor (heparin), sarco(endo)plasmic Ca 2ϩ -ATPase (thapsigargin), and Na ϩ /Ca 2ϩ exchanger (KB-R7943). Electron-microscopic examination of beating cardiomyocytes revealed progressive breakdown of Z disks. Immunohistochemical analysis and Western blot confirmed that disappearance of Z disk constituent proteins (␣-actinin, desmin, and tropomyosin) preceded degradation of other cytoskeletal proteins. It thus appears that, in adult cardiomyocyte apoptosis, Ca 2ϩ transients mediate apoptotic beating and efficient sarcomere destruction initiated by Z disk breakdown. apoptosis; calcium regulation; cardiac myocytes; sarcomere; Z disk SEVERAL REPORTS have suggested that apoptosis among cardiomyocytes plays an important role in the progression of cardiovascular disease (1,7,11). This idea remains controversial, however, because the ultrastructural changes characteristic of apoptosis have only rarely been seen in cardiomyocytes from diseased hearts (8,16,34). However, cardiomyocyte apoptosis can be induced in vitro by a variety of stimuli. For instance, we and others previously described Fas-induced, hypoxia-induced, and ␤-adrenergic pathway-stimulated apoptosis in cultured adult cardiomyocytes (5,15,17,22).Adult cardiomyocytes are terminally differentiated cells that are highly specialized in terms of structure and function. They express contractile proteins and a particularly well-developed cytoskeleton that are tightly packed into the cytoplasm and are sensitive to the Ca 2ϩ load, mediating continual contraction and relaxation in vivo. In an earlier study, we used serial video and electron microscopy to show several unique features of apoptosis in adult cardiomyocytes, including the rhythmic contraction and relaxation (beating) that precede cellular deformation, accelerate as the cell shrinks, and are accompan...

The L-type Ca2+ Channels Blocker Nifedipine Represses Mesodermal Fate Determination in Murine Embryonic Stem Cells

“…Likewise, previous studies demonstrated that nifedipine inhibits rather than induces cell apoptosis of CMs [48]. Interestingly, BayK8644 only showed a tendency to increase the yield of CMs from ES cells at any differentiation stage which was more pronounced in iPS cells, suggesting that single LTCCs activity may be already near its maximum.…”

Substrate stiffness affects sarcomere and costamere structure and electrophysiological function of isolated adult cardiomyocytes

“…The z-disk complex is a complicated array of proteins that also includes candidates for the stretch sensing mechanism, with α-actinin forming the backbone of the structure. Recent studies have indicated that the z-disk is among the initial targets for deterioration during isoproterenol-induced adult cardiomyocyte apoptosis [23], suggesting that z-disk integrity is a crucial indicator of cardiomyocyte function.…”

Low extracellular K+ increases intracellular Ca2+ oscillation and injury by activating the reverse mode Na+–Ca2+ exchanger and inhibiting the Na+, K+ ATPase in rat cardiomyocytes

“…The results indicated an increase of reverse-mode NCX activity mediated the more [Ca 2+ ] i oscillations, thus resulting in the exacerbating reperfusion injury by low K + . It was also found that Nifedipine, a selective inhibitor of Ltype Ca 2+ channel, at the concentration of 1 μM [24,25], failed to prevent increased occurrence of [Ca 2+ ] i oscillations, and decreased cell length recovery and cell viability by reperfusion with low K + (Fig. 1B, C, and D), indicating that L-type Ca 2+ channel is not involved in the exacerbating reperfusion injury by low K + .…”