Kir2.1 inward rectifier K+ channels are regulated independently by protein kinases and ATP hydrolysis.
Second messenger regulation of IRK1 (Kir2.1) inward rectifier K+ channels was investigated in giant inside-out patches from Xenopus oocytes. Kir2.1-mediated currents that run down completely within minutes upon excision of the patches could be partly restored by application of Mg-ATP together with > 10 microM free Mg2+ to the cytoplasmic side of the patch. As restoration could not be induced by the ATP analogs AMP-PNP or ATP gamma S, this suggests an ATPase-like mechanism. In addition to ATP, the catalytic subunit of cAMP-dependent protein kinase (PKA) induced an increase in current amplitude, which could, however, only be observed if channels were previously or subsequently stimulated by Mg-ATP and free Mg2+. This indicates that functional activity of Kir2.1 channels requires both phosphorylation by PKA and ATP hydrolysis. Moreover, currents could be down-regulated by N-heptyl-5-chloro-1-naphthalenesulfonamide, a specific stimulator of protein kinase C (PKC), suggesting that PKA and PKC mediate inverse effects on Kir2.1 channels. Regulation of Kir2.1 channels described here may be an important mechanism for regulation of excitability.
Fakler
B
B
Department of Sensory Biophysics, ENT-Hospital, University of Tübingen, Germany.
Brändle
U
U
Glowatzki
E
E
Zenner
H P
HP
Ruppersberg
J P
JP
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D017931:DNA Primers / Q000737:chemistry; D015640:Ion Channel Gating; D008274:Magnesium / Q000378:metabolism; D008969:Molecular Sequence Data; D009865:Oocytes; D010766:Phosphorylation; D015221:Potassium Channels / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D011493:Protein Kinase C / Q000378:metabolism*; D015290:Second Messenger Systems; D014982:Xenopus laevis
D017931:DNA Primers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D008274:Magnesium