Differences in regulation between nuclear and cytoplasmic Ca2+ in cultured smooth muscle cells.
The free Ca2+ concentrations in the nucleus ([Ca2+]n) and cytoplasm ([Ca2+]c) of cultured smooth muscle cells were estimated using the fluorescent dye indo-1 and the ACAS 570 confocal laser microscope. In resting DDT1MF2 smooth muscle cells [Ca2+]n was found to be lower than [Ca2+]c. Both values increased transiently in response to histamine (100 microM), but during this stimulation [Ca2+]n exceeded [Ca2+]c. Maximal increase of [Ca2+]n was observed in the center of the nucleus, and a maximal increase of [Ca2+]c was observed in the immediate vicinity of the plasma membrane. A similar response was obtained with other agonists, such as carbachol or ATP. Comparable results with ATP were obtained in cultured aorta cells. The differential rise of [Ca2+]n over [Ca2+]c in DDT1MF2 cells did not occur during either spontaneous release of Ca2+ or Ca2+ release induced by caffeine (7.5 mM). The differential rise during histamine stimulation was abolished by the presence of the intercalating substance ethidium bromide. Thapsigargin, a presumed specific inhibitor of the endoplasmic reticulum Ca(2+)-Mg(2+)-adenosine-triphosphatase, abolished the Ca2+ gradient between nucleus and cytosol at rest. During subsequent histamine stimulation the Ca2+ increase was largely blocked in both compartments and attained similar levels. We propose that the lower value of [Ca2+]n at rest is dependent on an active Ca2+ extrusion system. The differential rise of [Ca2+]n over [Ca2+]c during agonist stimulation can be explained by an influx of Ca2+ from perinuclear stores and/or by a release of intranuclear Ca2+ possibly mediated by a process dependent on the inositol lipid metabolism.
Himpens
B
B
Department of Physiology, K. U. Leuven, Gasthuisberg, Louvain, Belgium.
De Smedt
H
H
Droogmans
G
G
Casteels
R
R
D000818:Animals; D001011:Aorta / Q000166:cytology / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D004996:Ethidium / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D012146:Rest; D015398:Signal Transduction; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D013997:Time Factors; D014407:Tumor Cells, Cultured
D013729:Terpenes; D002110:Caffeine; D019284:Thapsigargin; D006632:Histamine; D000252:Calcium-Transporting ATPases; D004996:Ethidium; D002118:Calcium