Two-dimensional and line-scan images of cytoplasmic and nuclear free Ca
2+ movements in cardiac myocytes were obtained during normal Ca
2+ transients and abnormal Ca
2+ oscillations with confocal microscopy and Ca
2+ sensitive fluoroprobes. When the myocardial cells were field-stimulated at 0.5 Hz, nuclear Ca
2+ was observed to rise and fall following cytoplasmic Ca
2+ with an obvious delay. Isoproterenol significantly decreased, while cyclopiazonic acid significantly increased, the time required for Ca
2+ decay; the changes were larger in the cytoplasm than in the nucleus. When the cells were voltage-clamped at 0 mV for 3 sec, no difference in the steady state Ca
2+ concentration was observed between the cytoplasm and the nucleus. Nuclear Ca
2+ was also observed to increase following a Ca
2+ wave—a local increase in free Ca
2+ propagating within the cytoplasm—with a delay. When arrhythmic Ca
2+ oscillations in the cytoplasm were induced by aconitine, they were propagated into the nucleus; treatment with KB-R7943 abolished the abnormal Ca
2+ oscillations both in the cytoplasm and in the nucleus. Thus, we demonstrated in isolated myocardial cells that normal and abnormal Ca
2+ oscillations in the cytoplasm, although insulated by the nuclear envelope, are propagated into the nucleus, a mechanism through which factors affecting cytoplasmic Ca
2+ may influence intranuclear events.
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