Three homologous subunits form a high affinity peptide-gated ion channel in Hydra.
Recently, three ion channel subunits of the degenerin (DEG)/epithelial Na(+) channel (ENaC) gene family have been cloned from the freshwater polyp Hydra magnipapillata, the Hydra Na(+) channels (HyNaCs) 2-4. Two of them, HyNaC2 and HyNaC3, co-assemble to form an ion channel that is gated by the neuropeptides Hydra-RFamides I and II. The HyNaC2/3 channel is so far the only cloned ionotropic receptor from cnidarians and, together with the related ionotropic receptor FMRFamide-activated Na(+) channel (FaNaC) from snails, the only known peptide-gated ionotropic receptor. The HyNaC2/3 channel has pore properties, like a low Na(+) selectivity and a low amiloride affinity, that are different from other channels of the DEG/ENaC gene family, suggesting that a component of the native Hydra channel might still be lacking. Here, we report the cloning of a new ion channel subunit from Hydra, HyNaC5. The new subunit is closely related to HyNaC2 and -3 and co-localizes with HyNaC2 and -3 to the base of the tentacles. Coexpression in Xenopus oocytes of HyNaC5 with HyNaC2 and -3 largely increases current amplitude after peptide stimulation and affinity of the channel to Hydra-RFamides I and II. Moreover, the HyNaC2/3/5 channel has altered pore properties and amiloride affinity, more similarly to other DEG/ENaC channels. Collectively, our results suggest that the three homologous subunits HyNaC2, -3, and -5 form a peptide-gated ion channel in Hydra that could contribute to fast synaptic transmission.
Department of Physiology, RWTH Aachen University, Aachen, Germany.
Stefan
S
Dürrnagel
Anne
A
Kuhn
Charisios D
CD
Tsiairis
Michael
M
Williamson
Hubert
H
Kalbacher
Cornelis J P
CJ
Grimmelikhuijzen
Thomas W
TW
Holstein
Stefan
S
Gründer
D000584:Amiloride / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D062626:Degenerin Sodium Channels; D053503:Epithelial Sodium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D005247:Feeding Behavior / Q000187:drug effects / Q000502:physiology; D005260:Female; D006829:Hydra / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D017403:In Situ Hybridization; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D026941:Sodium Channel Blockers / Q000494:pharmacology; D014982:Xenopus laevis
D062626:Degenerin Sodium Channels; D053503:Epithelial Sodium Channels; D007473:Ion Channels; D009419:Nerve Tissue Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; D026941:Sodium Channel Blockers; D000584:Amiloride