Two-dimensional images of cytoplasmic and nuclear free Ca
2+ movements in cardiac myocytes were obtained at 67-msec intervals using a Ca
2+-sensitive fluorescence probe, indo-1, and a rapid scanning confocal laser microscope, Nikon RCM8000. Isolated guinea pig ventricular cells were loaded with indo-1 and stimulated at 0.5 Hz through patch pipettes. On stimulation, nuclear Ca
2+ concentration ([Ca
2+]) was observed to rise and fall following cytoplasmic [Ca
2+] with an obvious delay. Application of isoproterenol significantly increased the peak [Ca
2+] on stimulation in both the cytoplasm and nucleus with no substantial change in the basal [Ca
2+]; the increase in peak [Ca
2+]produced by application of isoproterenol was larger in the cytoplasm than in the nucleus. Under a low [Na
+] condition, the basal [Ca
2+] was increased from the control values in both the cytoplasm and nucleus; no difference in basal [Ca
2+] was observed between the two regions. The increase in peak [Ca
2+] by low [Na
+] in the cytoplasm was significantly larger than that in the nucleus. When the cells were voltage clamped at 0 mV for 3 sec, no difference in the steady state [Ca
2+] was observed between the cytoplasm and nucleus. Nuclear [Ca
2+] was also observed to increase following a Ca
2+ wave, a local increase in [Ca
2+] propagating within the cytoplasm, with a delay. Thus, we demonstrated in isolated myocardial cells that cytoplasmic Ca
2+ movements, although hampered 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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