An inositol 1,4,5-trisphosphate-sensitive Ca2+ pool in liver nuclei

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Recent studies identified an ATP- and calmodulin-dependent Ca2+ uptake system in rat liver nuclei.
• This system influences free Ca2+ concentration within the nuclear matrix.

Purpose of the Study:

• To investigate the capacity of liver nuclei to sequester and buffer Ca2+.
• To determine the role of the nucleus in regulating cytosolic free Ca2+ concentration.
• To examine the effect of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] on nuclear Ca2+ levels.

Main Methods:

• Investigated Ca2+ sequestration and buffering by isolated rat liver nuclei.
• Utilized Ins(1,4,5)P3 to stimulate Ca2+ release from nuclei.
• Analyzed Ca2+ reuptake into nuclear compartments.

Main Results:

• Liver nuclei exhibit significant Ca2+ sequestration and buffering capabilities.
• Ins(1,4,5)P3 stimulates the release of a portion of nuclear Ca2+.
• A transient decrease in intranuclear free Ca2+ concentration follows Ins(1,4,5)P3 stimulation.
• Ca2+ is subsequently reuptaken into an Ins(1,4,5)P3-insensitive nuclear compartment.
• Demonstrated the existence of at least two distinct Ca2+ pools within liver nuclei.

Conclusions:

• Liver nuclei play a role in regulating cytosolic free Ca2+ concentration.
• Ins(1,4,5)P3 releases Ca2+ from a specific nuclear pool, indicating nuclear Ca2+ signaling.
• These findings support a role for the nucleus in modulating cytosolic Ca2+ levels in response to agonists.
• Nuclear Ca2+ regulation by second messengers may influence hormone-mediated intranuclear processes.