Hikaru Tanaka (1), Toru Kawanishi (2), Yoshimitsu Kato (1), Ryu Nakamura (3) and Koki Shigenobu (1)
(1) Department of Pharmacology, Toho University School of Pharmaceutical Sciences, Funabashi, Chiba 274, Japan (2) Division of Biochemistry and Biologicals, National Institute of Health Sciences, Tokyo 158, Japan (3) Microscopes Development Department, Nikon Corporation, Yokohama 244, Japan
Abstract: Two-dimensional images of cytoplasmic and nuclear free Ca2+ movements in cardiac myocytes were obtained at 67-msec intervals using a Ca2+-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 Ca2+ concentration ([Ca2+]) was observed to rise and fall following cytoplasmic [Ca2+] with an obvious delay. Application of isoproterenol significantly increased the peak [Ca2+] on stimulation in both the cytoplasm and nucleus with no substantial change in the basal [Ca2+]; the increase in peak [Ca2+] produced by application of isoproterenol was larger in the cytoplasm than in the nucleus. Under a low [Na+] condition, the basal [Ca2+] was increased from the control 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, no difference in the steady state [Ca2+] was observed between the cytoplasm and nucleus. Nuclear [Ca+] was also observed to increase following a Ca2+ wave, a local increase in [Ca2+] propagating within the cytoplasm, with a delay. Thus, we demonstrated in isolated myocardial cells that cytoplasmic Ca2+ movements, although hampered by the nuclear envelope, are propagated into the nucleus, a mechanism through which factors affecting cytoplasmic Ca2+ may influence intranuclear events.
Confocal microscopy, Calcium ion, Indo-1, Myocardium, Nucleus
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