Kinetics of nucleocytoplasmic Ca2+ transients in DDT1 MF-2 smooth muscle cells.
The free calcium concentrations in the nucleus ([Ca2+]n) and in the cytoplasm ([Ca2+]c) of cultured DDT1 MF-2 smooth muscle cells were estimated using the fluorescent dye indo-1. With the use of confocal microscopy, line scans were made during the onset and the differential rise of the Ca2+ signal elicited by the agonists histamine and ATP. The results confirm our earlier findings that in these cells [Ca2+]n at rest was lower than [Ca2+]c. The present experiments show that this gradient over the nuclear envelope was also preserved in Ca(2+)-free solution containing 2 mM EGTA, underlining the selective barrier function of the nuclear envelope. During stimulation with histamine, an early Ca2+ rise in the vicinity of the nuclear envelope was found in contrast to the delayed Ca2+ rise 2 microns away on both sides of the envelope. This suggests the release of Ca2+ stored in the envelope and the perinuclear sarcoplasmic reticulum. The time course for reaching a uniform Ca2+ concentration ([Ca2+]u = [Ca2+]n = [Ca2+]c) in the nuclear and cytosolic compartment varied with the agonist used for stimulation and was dependent on the external Ca2+ concentration. The value of this uniform Ca2+ concentration itself was, however, independent of the type of stimulation. After reaching [Ca2+]u, a further rise occurred with [Ca2+]n becoming larger than [Ca2+]c. It is postulated that a critical Ca2+ concentration must be reached to induce this differential Ca2+ rise by releasing Ca2+ from an intranuclear Ca2+ store.
Himpens
B
B
Physiological Laboratory, K. U. Leuven, Belgium.
De Smedt
H
H
Casteels
R
R
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D002460:Cell Line; D002467:Cell Nucleus / Q000502:physiology*; D006224:Cricetinae; D003593:Cytoplasm / Q000502:physiology*; D004594:Electrophysiology; D006632:Histamine / Q000494:pharmacology; D007700:Kinetics; D008647:Mesocricetus; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism / Q000502:physiology*
D006632:Histamine; D000255:Adenosine Triphosphate; D002118:Calcium