Spatial features of calcium transients during early and delayed afterdepolarizations.
Although changes in intracellular Ca2+ concentration ([Ca2+]i) are spatially heterogeneous during spontaneous contraction in mammalian cardiac muscle, it has not yet been observed how [Ca2+]i changes spatially within cardiac myocytes during delayed (DADs) and early (EADs) afterdepolarizations. The aim of this study is to characterize the spatial features of the increase in [Ca2+]i during such afterdepolarizations and to understand the ionic mechanisms responsible for them. Myocytes were enzymatically isolated from guinea pig ventricles and loaded with fura 2-acetoxymethylester, the Ca2+ fluorescence indicator dye. Membrane potential was recorded with a conventional microelectrode technique, and spatiotemporal changes in fura 2 fluorescence and cell length were recorded using a digital television system. After superfusion with potassium-free Tyrode solution, DADs and EADs were induced. During DADs, fluorescence transients were heterogeneous within myocytes (n = 11). Furthermore, they often propagated within myocytes as if they were "waves." In contrast, during EADs, fluorescence transients showed no waves within myocytes but rather showed synchronous changes throughout the myocytes (n = 15). The results of this study suggest that the spatial features of the increase in [Ca2+]i differ between the DADs and EADs. We concluded from these differing features that the ionic mechanisms responsible for the two triggered activities are different.
Miura
M
M
First Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
Ishide
N
N
Oda
H
H
Sakurai
M
M
Shinozaki
T
T
Takishima
T
T
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002469:Cell Separation; D004594:Electrophysiology; D016257:Fura-2; D006321:Heart / Q000502:physiology*; D007552:Isotonic Solutions / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D010477:Perfusion; D011188:Potassium / Q000494:pharmacology; D011930:Reaction Time; D014018:Tissue Distribution
D007552:Isotonic Solutions; C037692:Tyrode's solution; D011188:Potassium; D002118:Calcium; D016257:Fura-2