ATP released from astrocytes during swelling activates chloride channels

Area of Science:

• Neuroscience
• Cell Physiology
• Biochemistry

Background:

• Astrocytes play a role in neuronal excitability and calcium wave propagation through ATP release.
• Cell swelling in other cell types triggers ATP release and activates volume-sensitive chloride currents (I(Cl,swell)) via autocrine purinergic signaling.
• Astrocytes exhibit regulatory volume decrease mechanisms involving metabolite efflux and ion currents.

Purpose of the Study:

• To investigate the autocrine role of ATP in activating I(Cl,swell) in cultured astrocytes exposed to hypo-osmotic solutions (HOS).
• To identify the specific purinergic receptors and transport mechanisms involved in ATP-mediated I(Cl,swell) activation during astrocyte swelling.

Main Methods:

• Whole-cell patch-clamp recordings were used to measure chloride currents in cultured astrocytes.
• Apyrase was employed to degrade extracellular ATP and assess its role in HOS-activated currents.
• Specific P2Y and P2X receptor agonists and antagonists were utilized to identify receptor subtypes involved.
• Luciferin-luciferase assays measured direct ATP release from astrocytes.
• Inhibitors of multidrug resistance proteins (MRPs) were used to investigate the efflux pathway of ATP.

Main Results:

• HOS-induced I(Cl,swell) was inhibited by apyrase, indicating a role for extracellular ATP.
• ATP and P2Y agonists (ADPbetaS, ADP) mimicked HOS-induced currents, while P2U and P2X agonists were ineffective.
• P2Y1-like receptors were implicated in ATP-mediated current activation, as shown by antagonist effects (suramin, RB2, PPADS).
• MRP inhibitors (probenecid, indomethacin, MK-571) potently inhibited I(Cl,swell).
• MK-571 reduced HOS-induced ATP release from astrocytes.

Conclusions:

• ATP release, mediated by multidrug resistance proteins (MRPs), contributes to the activation of volume-sensitive chloride currents (I(Cl,swell)) in astrocytes during hypo-osmotic swelling.
• This process involves the autocrine activation of P2Y1-like purinergic receptors.
• The findings elucidate a novel autocrine signaling pathway in astrocytes responding to cell volume changes.