Differences in regulation between nuclear and cytoplasmic Ca2+ in cultured smooth muscle cells

• Published in: The American journal of physiology Vol. 263; no. 1 Pt 1; p. C95
• Main Authors: Himpens, B, De Smedt, H, Droogmans, G, Casteels, R
• Format: Journal Article
• Language: English
• Published: United States 01.07.1992
• Subjects: Animals; Aorta - cytology; Aorta - metabolism; Caffeine - pharmacology; Calcium - metabolism; Calcium-Transporting ATPases - antagonists & inhibitors; Cell Nucleus - metabolism; Cytoplasm - metabolism; Ethidium - pharmacology; Histamine - pharmacology; Muscle, Smooth - cytology; Muscle, Smooth - metabolism; Rest; Signal Transduction; Terpenes - pharmacology; Thapsigargin; Time Factors; Tumor Cells, Cultured
• ISSN: 0002-9513
• DOI: 10.1152/ajpcell.1992.263.1.c95

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.