The ASIC3/P2X3 cognate receptor is a pain-relevant and ligand-gated cationic channel

2018. május 14.

Acid-sensing ion channels (ASICs) belong to the epithelial sodium channels, which are gated by protons and exhibit a cationic permeability with marked preference for Na+ over K+. P2X receptors, having 7 mammalian subunits (P2XR1–7), are ligand gated non-selective cation channels and are sensitive to adenosine triphosphate (ATP). In spite of their different amino acid sequences, the two receptor types have a similar molecular structure and each co-assemble into homo-or heteromeric functional ion channels consisting of three individual subunits. Among ASICs and P2XRs, the acid-sensing ion channel 3 (ASIC3) and P2X3 receptors (P2X3Rs) show a partially overlapping expression in sensory neurons, which raise the possibility that the two types of ion channels interact with each other. In this study, the group of Peter Illes (University of Leipzig) in collaboration with the lab of Beáta Sperlágh (Laboratory of Molecular Pharmacology, IEM HAS) asked, whether ASIC3/P2X3 subunits might form a trimeric channel or the two receptors associate to a multiprotein complex, allowing a state-dependent propagation of allosteric states and communicating the gating movements of one channel to the other. Here we report that both recombinant and native receptors interact with each other in multiple ways. Current measurements with the patch-clamp technique prove that ASIC3 stimulation strongly inhibits the P2X3R current partly by a Ca2+-dependent mechanism. The proton-binding site is critical for this effect and the two receptor channels appear to switch their ionic permeabilities during activation. Co-immunoprecipation proves the close association of the two protein structures. BN-PAGE and SDS-PAGE analysis is also best reconciled with the view that ASIC3 and P2X3Rs form a multiprotein structure. Finally, in vivo measurements in rats revealed the summation of pH and purinergically induced pain. The results suggests that the receptor subunits do not appear to form a heteromeric channel, but tightly associate with each other to form a protein complex, mediating unidirectional inhibition.

Nature Communications volume 9, Article number: 1354 (2018)