RESTRICTED PROPAGATION OF CYTOPLASMIC CA2-PIG CARDIAC MYOCYTES AS REVEALED BY RAPID-SCANNING CONFOCAL MICROSCOPY AND INDO-1( OSCILLATION INTO THE NUCLEUS IN GUINEA)

Two-dimensional images of cytoplasmic and nuclear free Ca2+ movements in cardiac myocytes were obtained at 67-msec intervals using a Ca2+-se nsitive fluorescence probe, indo-1, and a rapid scanning confocal lase r microscope, Nikon RCM8000. Isolated guinea pig ventricular cells wer e loaded with indo-1 and stimulated at 0.5 Hz through patch pipettes. On stimulation, nuclear Ca2+ concentration ([Ca2+]) was observed to ri se and fall following cytoplasmic [Ca2+] with an obvious delay. Applic ation of isoproterenol significantly increased the peak [Ca2+] on stim ulation in both the cytoplasm and nucleus with no substantial change i n the basal [Ca2+]; the increase in peak [Ca2+] produced by applicatio n of isoproterenol was larger in the cytoplasm than in the nucleus. Un der a low [Na+] condition, the basal [Ca2+] was increased from the con trol values in both the cytoplasm and nucleus; no difference in basal [Ca2+] was observed between the two regions. The increase in peak [Ca2 +] 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, n o difference in the steady state [Ca2+] was observed between the cytop lasm and nucleus. Nuclear [Ca2+] was also observed to increase followi ng a Ca2+; wave, a local increase in [Ca2+] propagating within the cyt oplasm, with a delay. Thus, we demonstrated in isolated myocardial cel ls that cytoplasmic Ca2+ movements, although hampered by the nuclear e nvelope, are propagated into the nucleus, a mechanism through which fa ctors affecting cytoplasmic Ca2+ may influence intranuclear events.