Visualization of biphasic Ca2+ diffusion from cytosol to nucleus in contracting adult rat cardiac myocytes with an ultra-fast confocal imaging system.
In contracting cardiac myocytes, the rapid changes in cytosolic and nuclear Ca2+ make it difficult to determine whether the nuclear Ca2+ transient is caused by diffusion from the cytosol or by Ca2+ release channels on the inner nuclear membrane, or both. The propagation mechanism in the nucleoplasm also remains unknown. We have developed an ultra-fast Nipkow confocal imaging system able to acquire two-dimensional images at approximately 4 ms/full frame speed and employed it to analyze Ca2+ waves and the dynamics of the cytosolic and nuclear Ca2+ transients after electrical stimulation of cardiac myocytes. The pattern of nuclear Ca2+ upon stimulation was well described by a mathematical model of Ca2+ diffusion across the nuclear envelope. No evidence of Ca2+ release from perinuclear Ca2+ stores was obtained. The Ca2+ diffusion constant appeared to change during contraction, with essentially free diffusion of Ca2+ through nuclear pore complexes at low cytosolic Ca2+ and partially restricted diffusion at high cytosolic Ca2+. The Ca2+ in the nucleoplasm propagated by diffusion and no Ca2+ release phenomena were seen in the nucleus.
Genka
C
C
Department of Physiology, School of Medicine, Tokai University, Kanagawa, Japan.
Ishida
H
H
Ichimori
K
K
Hirota
Y
Y
Tanaami
T
T
Nakazawa
H
H
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D018613:Microscopy, Confocal / Q000295:instrumentation* / Q000379:methods*; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D005456:Fluorescent Dyes; D002118:Calcium