ATP release during cell swelling activates a Ca²⁺-dependent Cl^- current by autocrine mechanism in mouse hippocampal...

Area of Science:

• Neuroimmunology
• Cell Physiology
• Ion Channel Function

Background:

• Microglia, the brain's resident immune cells, dynamically survey the brain parenchyma using extending and retracting processes.
• Chloride (Cl^-) channels activated by cell stretch/swelling are implicated in microglia physiology, including shape changes, proliferation, differentiation, and migration.
• The molecular identity and functional characteristics of these swelling-activated Cl^- channels in microglia remain largely uncharacterized.

Purpose of the Study:

• To investigate the properties of swelling-activated currents in microglia.
• To elucidate the molecular mechanisms underlying the activation and function of these currents in microglia.
• To understand the role of these currents in microglia's ability to monitor the brain parenchyma.

Main Methods:

• Whole-cell patch-clamp electrophysiology on microglia from acute hippocampal slices of Cx3cr1^+/GFP mice.
• Imaging techniques to observe cellular responses.
• Application of mild hypotonic solutions to induce cell swelling.

Main Results:

• Mild hypotonic exposure induced an outward rectifying current, primarily carried by Cl^- ions and dependent on intracellular Ca²⁺.
• This swelling-activated current was essential for microglia process extension towards damage signals.
• A purine-dependent mechanism involving swelling-induced ATP release and autocrine purinergic receptor stimulation was identified as an amplification pathway for current activation.

Conclusions:

• This study provides the first functional characterization of stretch/swelling-activated currents in native microglia.
• These currents are crucial for microglia's surveillance function in the brain parenchyma.
• An autocrine purinergic signaling pathway amplifies the activation of these ion channels, highlighting a novel mechanism in microglia response.