Stoichiometry of Acid-Sensing Ion Channel (ASIC) Pharmacology

Acid-sensing Ion Channels (ASICs) are sodium-selective channels stemming from the Epithelial Sodium Channel superfamily of ligand-gated ion channels. ASICs are activated through extracellular acidification and as such, act as prominent receptors for protons in the central and peripheral nervous system. These channels play physiological roles like learning, memory, fear conditioning and nociception, while having significant neurodegenerative effects in acidosis-related diseases including, but not limited to, cerebral ischemia, multiple sclerosis and Parkinson's. By their very nature, ASICs have immense potential as therapeutic targets for various physiological and pathophysiological conditions. Understanding the mechanism of the channels function and how this function can be altered through pharmacological means is of utmost importance for the development of ASIC-based therapeutics. As ASICs exist as homo- or heterotrimeric channels, an important facet is determining the necessary number of functional subunits required for channel function and modulation. Our study looks to uncover the functional stoichiometry of ASIC1a pharmacological modulation through the use of a concatenated human ASIC1a trimer measured by outside-out patch clamp electrophysiology paired with ultrafast perfusion. To test the necessary stoichiometry of pharmacological potentiation and inhibition, we tested 4 commonly used ASIC1a-modulating compounds for their effects on the channel when binding has been abrogated in one, two or three subunits of the concatenated channel. These findings provide a significant leap forward for our understanding of ASIC1a pharmacology.