Heteromeric Assembly of Acid-sensitive Ion Channel and Epithelial Sodium Channel Subunits

Robert H Meltzer,Dale J Benos,Catherine M Fuller,Susan J Anderson,Niren Kapoor,Yawar J Qadri

doi:10.1074/jbc.m703825200

Robert H Meltzer, Dale J Benos + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m703825200

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Abstract

Amiloride-sensitive ion channels are formed from homo- or heteromeric combinations of subunits from the epithelial Na+ channel (ENaC)/degenerin superfamily, which also includes the acid-sensitive ion channel (ASIC) family. These channel subunits share sequence homology and topology. In this study, we have demonstrated, using confocal fluorescence resonance energy transfer microscopy and co-immunoprecipitation, that ASIC and ENaC subunits are capable of forming cross-clade intermolecular interactions. We have also shown that combinations of ASIC1 with ENaC subunits exhibit novel electrophysiological characteristics compared with ASIC1 alone. The results of this study suggest that heteromeric complexes of ASIC and ENaC subunits may underlie the diversity of amiloride-sensitive cation conductances observed in a wide variety of tissues and cell types where co-expression of ASIC and ENaC subunits has been observed.

Highlights

Amiloride-sensitive ion channels have been identified in a wide variety of cell lines and tissue types
acid-sensitive ion channel (ASIC) subunits were initially identified in the brain and dorsal root ganglion by sequence homology with known epithelial Na؉ channel (ENaC) subunits [12]
In order to determine heteromultimeric associations between ASIC and ENaC subunits, combinations of fluorescent tagged subunits were co-expressed in CHO K1 cells

Summary

Dorsal root ganglia ϩ

Intermolecular associations between co-expressed ion channel subunits have been demonstrated by confocal FRET microscopy and by coimmunoprecipitation. The electrophysiological properties of channels comprised of ASIC1 and ENaC subunits have been determined by two-electrode voltage clamp of cRNA-injected Xenopus laevis oocytes. We present evidence that ASIC and ENaC subunits can intermix promiscuously and that ion channel properties, including cation selectivity and pharmacological inhibition, are affected by the subunit composition of the expressed channels

EXPERIMENTAL PROCEDURES

RESULTS

That ASIC and ENaC Subunits