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  • Title: Visualization of biphasic Ca2+ diffusion from cytosol to nucleus in contracting adult rat cardiac myocytes with an ultra-fast confocal imaging system.
    Author: Genka C, Ishida H, Ichimori K, Hirota Y, Tanaami T, Nakazawa H.
    Journal: Cell Calcium; 1999 Mar; 25(3):199-208. PubMed ID: 10378081.
    Abstract:
    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.
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