THE CALCIUM STORE IN THE NUCLEAR-ENVELOPE

The nuclear envelope has a relatively small volume, but is connected u p to the vastly larger endoplasmic reticulum. The Ca2+ concentration i n the lumen of the interconnected nuclear envelope and endoplasmic ret iculum network is in the resting state maintained at a level of more t han 100 mu M. There are specific Ca2+ release channels present in the inner nuclear membrane that can be activated by inositol trisphosphate or cADP ribose. The system, therefore, allows selective release of Ca 2+ into the nucleoplasm which could be important for the control of sp ecific types of gene expression.