Nucleoplasmic Ca(2+)loading is regulated by mobilization of perinuclear Ca(2+)

Area of Science:

• Cardiovascular Biology
• Cellular Physiology
• Molecular Cardiology

Background:

• Nucleoplasmic calcium (Ca2+) concentration is crucial for cellular functions.
• The perinuclear lumen's role in regulating nucleoplasmic Ca2+ has been largely unexplored.
• Specific Ca2+ pumps and channels in the inner and outer perinuclear membranes are implicated in Ca2+ transport.

Purpose of the Study:

• To investigate the role of perinuclear luminal Ca2+ pools in regulating nucleoplasmic Ca2+ concentration.
• To identify the molecular machinery involved in bi-directional Ca2+ fluxes across the nuclear envelope.
• To determine if the perinuclear lumen can autonomously regulate nucleoplasmic Ca2+.

Main Methods:

• Cultured 10-day-old embryonic chick ventricular cardiomyocytes.
• Confocal imaging techniques.
• Immunocytochemistry using antibodies for ryanodine-sensitive Ca2+ channels (RyR2) and sarco/endoplasmic reticulum Ca2+ ATPase (SERCA2)-pumps.
• Fluorescent probes (BODIPY derivatives, Fluo-3 AM) and pharmacological agents (ryanodine, thapsigargin, cyclopiazonic acid).

Main Results:

• RyR2 Ca2+ channels and SERCA2-pumps were highly localized to the nuclear envelope.
• Increases in extranuclear Ca2+ were localized to the nucleus.
• SERCA2-pump inhibitors (thapsigargin, cyclopiazonic acid) demonstrated concentration-dependent inhibition of nuclear Ca2+ loading.
• Ryanodine exhibited biphasic concentration-dependence on nuclear Ca2+ loading.
• Concomitant inhibition of SERCA2 and ryanodine treatment increased nuclear Ca2+ loading at low extranuclear Ca2+ concentrations.

Conclusions:

• The perinuclear lumen contains the molecular machinery (RyR2, SERCA2) for regulating nucleoplasmic Ca2+ fluxes.
• The perinuclear lumen can autonomously regulate nucleoplasmic Ca2+ concentration in embryonic chick ventricular cardiomyocytes.
• These findings provide insights into the spatial and temporal control of nuclear Ca2+ signaling.