Calcium homeostasis modulator 2 (Calhm2) as slowly activating membrane current channel in mouse B cells

Area of Science:

• Immunology
• Cell Physiology
• Molecular Biology

Background:

• An unidentified slow-activating voltage-dependent current (I_Calhm-L) was observed in mouse B lymphocytes.
• The Calhm family of ion channels was a potential candidate for this current.

Purpose of the Study:

• To investigate the nature and function of the I_Calhm-L in mouse B lymphocytes.
• To identify the specific Calhm family member responsible for I_Calhm-L.
• To determine the role of Calhm2 in purinergic signaling in B cells.

Main Methods:

• Reverse transcription-polymerase chain reaction (RT-PCR) to detect Calhm transcripts.
• Whole-cell patch-clamp electrophysiology to characterize the ion current.
• Heterologous expression of Calhm2 and Calhm6 in N2A cells.
• Calhm2 knockdown in Bal-17 cells.
• ATP release assays in primary mouse B cells.

Main Results:

• Calhm2 and Calhm6 transcripts were detected in mouse B lymphocytes.
• I_Calhm-L was augmented by heat, alkaline pH, and low extracellular calcium.
• Overexpression of Calhm2, but not Calhm6, in N2A cells recapitulated I_Calhm-L.
• Calhm2 knockdown abolished I_Calhm-L in Bal-17 cells.
• Calhm2 significantly contributed to ATP release in primary mouse B cells.

Conclusions:

• Calhm2 is identified as the voltage-dependent ion channel responsible for I_Calhm-L in mouse immune cells.
• Calhm2 plays a crucial role in purinergic signaling in B lymphocytes.
• This study elucidates a novel function of Calhm2 in the immune system.