A unique alkaline pH-regulated and fatty acid-activated tandem pore domain potassium channel (K₂P) from a marine sponge.
A cDNA encoding a potassium channel of the two-pore domain family (K(2P), KCNK) of leak channels was cloned from the marine sponge Amphimedon queenslandica. Phylogenetic analysis indicated that AquK(2P) cannot be placed into any of the established functional groups of mammalian K(2P) channels. We used the Xenopus oocyte expression system, a two-electrode voltage clamp and inside-out patch clamp electrophysiology to determine the physiological properties of AquK(2P). In whole cells, non-inactivating, voltage-independent, outwardly rectifying K(+) currents were generated by external application of micromolar concentrations of arachidonic acid (AA; EC(50) ∼30 μmol l(-1)), when applied in an alkaline solution (≥pH 8.0). Prior activation of channels facilitated the pH-regulated, AA-dependent activation of AquK(2P) but external pH changes alone did not activate the channels. Unlike certain mammalian fatty-acid-activated K(2P) channels, the sponge K(2P) channel was not activated by temperature and was insensitive to osmotically induced membrane distortion. In inside-out patch recordings, alkalinization of the internal pH (pK(a) 8.18) activated the AquK(2P) channels independently of AA and also facilitated activation by internally applied AA. The gating of the sponge K(2P) channel suggests that voltage-independent outward rectification and sensitivity to pH and AA are ancient and fundamental properties of animal K(2P) channels. In addition, the membrane potential of some poriferan cells may be dynamically regulated by pH and AA.
University of Richmond, Department of Biology, Richmond, VA 23173,  USA.
Gregory D
GD
Wells
Qiong-Yao
QY
Tang
Robert
R
Heler
Gabrielle J
GJ
Tompkins-MacDonald
Erica N
EN
Pritchard
Sally P
SP
Leys
Diomedes E
DE
Logothetis
Linda M
LM
Boland
D000468:Alkalies / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D059001:Aquatic Organisms / Q000187:drug effects / Q000502:physiology*; D016718:Arachidonic Acid / Q000494:pharmacology; D005227:Fatty Acids / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D015640:Ion Channel Gating / Q000187:drug effects*; D008969:Molecular Sequence Data; D009995:Osmosis / Q000187:drug effects; D010802:Phylogeny; D011161:Porifera / Q000187:drug effects / Q000502:physiology*; D024683:Potassium Channels, Tandem Pore Domain / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013696:Temperature; D014982:Xenopus laevis
D000468:Alkalies; D005227:Fatty Acids; D024683:Potassium Channels, Tandem Pore Domain; D016718:Arachidonic Acid