The Acid-sensitive Ionic Channel Subunit ASIC and the Mammalian Degenerin MDEG Form a Heteromultimeric H+-gated Na+ Channel with Novel Properties

Abstract

Proton-gated cation channels are acid sensors that are present in both sensory neurons and in neurons of the central nervous system. One of these acid-sensing ion channels (ASIC) has been recently cloned. This paper shows that ASIC and the mammalian degenerin MDEG, which are colocalized in the same brain regions, can directly associate with each other. Immunoprecipitation of MDEG causes coprecipitation of ASIC. Moreover, coexpression of ASIC and MDEG subunits in Xenopus oocytes generates an amiloride-sensitive H+-gated Na+ channel with novel properties (different kinetics, ionic selectivity, and pH sensitivity). In addition, coexpression of MDEG with mutants of the ASIC subunit can create constitutively active channels that become completely nonselective for Na+ versus K+ and H+-gated channels that have a drastically altered pH sensitivity compared with MDEG. These data clearly show that ASIC and MDEG can form heteromultimeric assemblies with novel properties. Heteromultimeric assembly is probably used for creating a diversity of H+-gated cation channels acting as neuronal acid sensors in different pH ranges.