Mast cell activation involves plasma membrane potential- and thapsigargin-sensitive intracellular calcium pools

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Intracellular calcium (Ca2+) signaling regulates numerous cellular processes, including mast cell degranulation.
• Understanding the precise mechanisms and sources of Ca2+ involved in mast cell activation is crucial for developing targeted therapies.

Purpose of the Study:

• To investigate the role and regulation of intracellular Ca2+ pools in rat peritoneal mast cells.
• To elucidate the mechanisms by which compound 48/80 and antigen induce histamine release, focusing on Ca2+ mobilization.

Main Methods:

• Monitoring cytosolic free calcium concentration ([Ca2+]i) using fura-2 in rat peritoneal mast cells.
• Utilizing manganese (Mn2+) and DTPA to differentiate extracellular vs. intracellular Ca2+ fluorescence quenching.
• Employing thapsigargin, a Ca(2+)-ATPase inhibitor, to probe intracellular Ca2+ stores.
• Assessing histamine release under varying extracellular Ca2+ concentrations and plasma membrane potentials.

Main Results:

• Compound 48/80 induced a biphasic increase in [Ca2+]i, with the sustained phase affected by extracellular factors.
• Thapsigargin abolished the transient [Ca2+]i increase, indicating involvement of microsomal Ca2+ stores.
• Maximum histamine release by compound 48/80 or antigen occurred without extracellular Ca2+ when cells were depolarized.
• Low-dose thapsigargin inhibited histamine release, while high doses induced Ca2+-dependent release, suggesting distinct Ca2+ influx pathways.

Conclusions:

• Mobilization of Ca2+ from thapsigargin-sensitive intracellular pools is sufficient to trigger histamine release induced by compound 48/80 or antigen.
• Plasma membrane potential modulates these intracellular Ca2+ pools, suggesting their proximity to the plasma membrane.
• These findings provide critical insights into the spatiotemporal regulation of Ca2+ in mast cell degranulation.