Phospholemman expression induces a hyperpolarization-activated chloride current in Xenopus oocytes.
A new type of chloride channel has been identified by functional expression of phospholemman, a 72-amino acid cardiac sarcolemmal protein with a single transmembrane domain. Xenopus oocytes injected with phospholemman RNA developed a chloride-selective current, which was activated by hyperpolarizing pulses. The current activated very slowly with a pronounced sigmoidal delay, did not inactivate, and increased in amplitude with trains of pulses, depolarized holding potentials, and low extracellular pH. Point mutations within the single transmembrane region abolished the sigmoidal delay of expressed currents. Phospholemman appears to be the smallest plasma membrane channel protein yet known. The structure is dissimilar to any chloride channel described thus far.
Moorman
J R
JR
Department of Medicine (Cardiology), University of Virginia, Charlottesville 22908.
Palmer
C J
CJ
John
J E
JE
Durieux
M E
ME
Jones
L R
LR
D000595:Amino Acid Sequence; D000818:Animals; D001345:Autoradiography; D015152:Blotting, Northern; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010063:Ovum / Q000502:physiology*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D014158:Transcription, Genetic; D014981:Xenopus
D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D008565:Membrane Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; C069141:phospholemman