NUCLEAR CALCIUM SIGNALING BY INDIVIDUAL CYTOPLASMIC CALCIUM PUFFS

It is known that the nucleoplasmic ionised calcium concentration (Ca-n ) nuclear functions such as transcription, although the source and nat ure of the signals which modulate Ca-n unclear, Using confocal imaging , we investigated the subcellular origin of Ca-n signals in Flue-3-loa ded HeLa cells. Our data indicate that all signals which increased Ca- n were of cytoplasmic origin. Ca-n was elevated during the propagation of global Ca waves within cells, More strikingly, we found that indiv idual cytoplasmic elementary release events e.g. Ca puffs, evoked by p hysiological levels of stimulation, caused transient Ca-n increases. S ignificantly, >70% of all Ca puffs originated within a 2-3 mu m perinu clear zone and propagated anisotropically across the entire nucleus, D ue to the relatively slow relaxation of Ca-n transients compared with those in the cytoplasm, repetitive perinuclear Ca puffs were integrate d into a 'staircase' of increasing Ca-n. Due to the effective diffusio n of Ca in the nucleoplasm, the nucleus served as a 'Ca tunnel', distr ibuting Ca to parts of the cytosol which were otherwise not within the cytoplasmic diffusion radii of Ca puffs, Given the close proximity of the majority of puff sites to the nucleus, it seems that the elementa ry Ca release system is designed to facilitate nuclear Ca signalling, Consequently, Ca-dependent regulation of nuclear function must be cons idered at the microscopic elementary level.