Development of excitation-contraction coupling in cardiomyocytes.
The excitation-contraction (E-C) coupling system during the development of heart can be investigated because of marked progression in electrophysiology and microfluorescence studies. During the developmental period, Ca2+ influx mediating the E-C coupling is mainly through the L-type Ca2+ channels. In the fetal period, T-type Ca2+ channels and the reverse mode of the Na-Ca exchange system also contribute to Ca2+ influx. These contributions probably reduce gradually until adulthood. The contraction of fetal cardiomyocytes has been thought to depend mainly on the Ca2+ influx. However, recent studies reveal that immature sarcoplasmic reticulum (SR) already works in the early fetal period. Ca2+ spark, a local and unitary movement of Ca2+, can be observed in adult cardiomyocytes by the use of a confocal microscope. On the other hand, no Ca2+ spark is observed in fetal cardiomyocytes. The frequency of Ca(2+)-spark evocation increases during the postnatal period. Therefore a close distance between the L-type Ca2+ channel and the SR Ca(2+)-release channel is essential to the establishment of the Ca2+ spark.
Tohse
Noritsugu
N
Department of Cellular Physiology and Signal Transduction, Sapporo Medical University School of Medicine, Sapporo, 060-8556 Japan. touse@sapmed.ac.jp
Seki
Sumihiko
S
Kobayashi
Takeshi
T
Tsutsuura
Masaaki
M
Nagashima
Masato
M
Yamada
Yoichi
Y
D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D006321:Heart / Q000196:embryology* / Q000502:physiology*; D006801:Humans; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology*
D015220:Calcium Channels