Involvement of Ca2+ waves in excitation-contraction coupling of rat atrial cardiomyocytes.
Two-dimensional and line-scan analyses of the early phase Ca2+ transients in rat cardiomyocytes were performed with a rapid-scanning laser confocal microscope and fluo-3 to elucidate the mechanism of activation of Ca2+ release from the sarcoplasmic reticulum in atrial myocytes which lack a well developed T-tubular network. On electrical stimulation of ventricular myocytes, Ca2+ concentration began to rise earliest at the Z-line level and became uniform throughout the cytoplasm within about 10 msec. In contrast, on stimulation of atrial myocytes, the earliest rise in Ca2+ occurred at the cell periphery and then spread to the cell interior; cytoplasmic Ca2+ became uniform after more than 30msec. The velocity of the propagation of rise in Ca2+ was 112 +/- 5.1 microm/sec (n = 10), which was similar to that of spontaneous Ca2+ waves observed in atrial and ventricular myocytes. No difference in frequency, amplitude and kinetics of spontaneous Ca2+ sparks was observed between the subsarcolemmal and central regions of atrial myocytes. Ryanodine concentration-dependently decreased the contractile force of isolated rat atrial and ventricular tissue preparations; the sensitivity was higher in atrial myocytes. The present study visualized the involvement of a propagated Ca2+-induced-Ca+ release mechanism in atrial but not ventricular myocytes. This difference may underlie some of the atrioventricular difference in response to physiological and pharmacological stimuli.
Tanaka
H
H
Department of Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan.
Masumiya
H
H
Sekine
T
T
Kase
J
J
Kawanishi
T
T
Hayakawa
T
T
Miyata
S
S
Sato
Y
Y
Nakamura
R
R
Shigenobu
K
K
D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D006325:Heart Atria / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D018613:Microscopy, Confocal; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure
D012433:Ryanodine