© 2003 by European Society of Cardiology
Copyright © 2003, European Society of Cardiology
Fetal and postnatal development of Ca2+ transients and Ca2+ sparks in rat cardiomyocytes
aDepartment of Cellular Physiology and Signal Transduction, Sapporo Medical University School of Medicine, Sapporo 060, Japan
bDepartment of Anesthesiology, Sapporo Medical University School of Medicine, Sapporo 060, Japan
sseki{at}kanazawa-med.ac.jp
* Corresponding author. Department of Anesthesiology, Kanazawa Medical University School of Medicine, Daigaku 1-1, Uchinada, Ishikawa, 920-0025 Japan. Tel.: +81-76-286-2211x3133; fax: +81-76-286-3475.
Objective: The aim of this study was to characterize the spatio-temporal dynamics of [Ca2+]i in rat heart in the fetal and neonatal periods. Methods: Using confocal scanning laser microscopy and the Ca2+ indicator fluo-3, we investigated Ca2+ transients and Ca2+ sparks in single ventricular myocytes freshly isolated from rat fetuses and neonates. T-tubules were labeled with a membrane-selective dye (di-8-ANEPPS). Spatial association of dihydropyridine receptors (DHPR) and ryanodine receptors (RyR) was also examined by double-labeling immunofluorescence. Results: Ca2+ transients in the fetal myocytes were characterized by slower upstroke and decay of [Ca2+]i compared to those in adult myocytes. The magnitude of fetal Ca2+ transients was decreased after application of ryanodine (1 µM) or thapsigargin (1 µM). However, Ca2+ sparks were rarely detected in the fetal myocytes. Frequent ignition of Ca2+ sparks was established in the 6–9-day neonatal period, and was predominantly observed in the subsarcolemmal region. The developmental change in Ca2+ sparks coincided with development of the t-tubule network. The immunofluorescence study revealed colocalization of DHPR and RyR in the postnatal period, which was, however, not observed in the fetal period. In the adult myocytes, Ca2+ sparks disappeared after disruption of t-tubules by glycerol incubation (840 mM). Conclusions: The sarcoplasmic reticulum (SR) of rat ventricular myocytes already functions early in the fetal period. However, ignition of Ca2+ sparks depends on postnatal t-tubule formation and resultant colocalization of DHPR and RyR.
KEYWORDS Calcium (cellular); Developmental biology; E–C coupling; Embryology; SR (function)
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