Molecular mechanism for sodium-dependent activation of G protein-gated K+ channels.
1. G protein-gated inwardly rectifying K+ (GIRK) channels are activated independently by Gbetagamma and internal Na+ via mechanisms requiring phosphatidylinositol phosphates. An aspartate (Asp) at position 226 in GIRK2 is crucial for Na+-dependent activation of GIRK1-GIRK2 heteromeric channels. We expressed wild-type and mutant GIRK1-GIRK2 channels in Xenopus oocytes and tested the effects of Na+ and neutralizing Asp226 on the functional interactions of the channels with phosphatidylinositol 4, 5-bisphosphate (PIP2). 2. The rate of inhibition of GIRK1-GIRK2 currents by application of anti-PIP2 antibody to inside-out membrane patches was slowed > 2-fold by the D226N mutation in GIRK2 and by increasing internal [Na+]. The reverse mutation in GIRK1 (N217D) increased the rate of inhibition. 3. The dose-response relationship for activation by purified PIP2 was shifted to lower concentrations in the presence of 20 mM Na+. 4. Three synthetic isoforms of PIP2, PI(4,5)P2, PI(3,4)P2 and PI(3,5)P2, activated GIRK channels with similar potencies. 5. We conclude that Na+ directly interacts with Asp226 of GIRK2 to reduce the negative electrostatic potential and promote the functional interaction of the channels with PIP2.
Ho
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Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QJ, UK.
Murrell-Lagnado
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D000818:Animals; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D019204:GTP-Binding Proteins / Q000502:physiology*; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D009865:Oocytes / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000502:physiology; D015221:Potassium Channels / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying; D051381:Rats; D012964:Sodium / Q000502:physiology*; D014982:Xenopus laevis
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D019269:Phosphatidylinositol 4,5-Diphosphate; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012964:Sodium; D019204:GTP-Binding Proteins