Restricted propagation of cytoplasmic Ca2+ oscillation into the nucleus in guinea pig cardiac myocytes as revealed by rapid scanning confocal microscopy and indo-1.
Two-dimensional images of cytoplasmic and nuclear free Ca2+ 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 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 [Ca2+] 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.
Tanaka
H
H
Department of Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan.
Kawanishi
T
T
Kato
Y
Y
Nakamura
R
R
Shigenobu
K
K
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002614:Chelating Agents; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D007211:Indoles; D008297:Male; D018613:Microscopy, Confocal; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*
D002614:Chelating Agents; D005456:Fluorescent Dyes; D007211:Indoles; C048960:indo-1; D002118:Calcium