Weak Acids as Endogenous Inhibitors of the Proton-Activated Chloride Channel

Area of Science:

• Physiology
• Molecular Biology
• Channelopathies

Background:

• The proton-activated chloride (PAC) channel is widely expressed and plays a role in physiological and pathophysiological processes sensitive to proton concentration.
• PAC channels are activated by strong acids via extracellular proton binding sites.

Purpose of the Study:

• To investigate the mechanism by which weak acids inhibit PAC channels.
• To identify the specific binding sites and molecular determinants involved in weak acid inhibition of PAC channels.

Main Methods:

• Whole-cell patch clamp electrophysiology on HEK293T cells, PAC-knockout cells expressing human PAC mutants, and hiPSC-derived cardiomyocytes.
• Examination of proton-induced cytotoxicity in HEK293T cells.
• Site-directed mutagenesis of the extracellular Arginine 93 residue in hPAC.

Main Results:

• Weak acids, including acetic, lactic, propionic, itaconic acid, and β-hydroxybutyrate, reversibly inhibit endogenous and recombinant PAC channels in a concentration- and pH-dependent manner.
• Mutating extracellular Arginine 93 to Alanine (hPAC-Arg93Ala) significantly reduced inhibition by certain weak acids, such as arachidonic acid.
• Lactic acid inhibited PAC channels but did not affect proton-induced cytotoxicity in HEK293 cells.

Conclusions:

• Weak acids inhibit PAC channels through a distinct extracellular mechanism involving Arginine 93.
• These findings highlight a novel regulatory pathway for PAC channels by endogenous weak acids, suggesting potential implications in various biological contexts.