The nucleus is insulated from large cytosolic calcium ion changes

Abstract

EXTRACELLULAR events regulate functions in the cell nucleus by means of calcium ions acting through effector enzymes^1–5. Recently, the traditional view of the nuclear pore as freely permeable to small ions^6,7has been questioned as a result of reports that nuclear calcium can be regulated independently of cytosolic calcium^8–12. We have used confocal microscopy of fluorescent Ca²⁺ indicators to investigate the Ca²⁺ dynamics between cytosol and nucleus in neurons. We find that a previously reported amplification of Ca²⁺ changes in the nucleus^13–16 is a measurement artefact. Small changes of cytosolic Ca²⁺ cause equally rapid changes in nuclear Ca²⁺, consistent with the free diffusion of Ca²⁺ through nuclear pores. In contrast, large cytosolic Ca²⁺ increases (above 300 nM) are attenuated in the nucleus. Our results show the nuclear envelope shapes but does not block the passage of Ca²⁺ signals from cytosol to nucleus.