Abstract
Inward rectifier K+ channels, which modulate electrical activity in many cell types, are regulated by protein kinases1,2, guanine-nucleotide-binding proteins (G proteins)3,4,5,6 and probably actin cytoskeleton7. Generation of phosphatidylinositol 4,5-bisphosphate (PIP2) by ATP-dependent lipid kinases is known to activate inward rectifier K+ channels in cardiac membrane patches8. Herewe report that several cloned inward rectifier K+ channels directly bind PIP2, and that this binding correlates with channel activity. Application of ATP or PIP2 liposomes activates the cloned channels. Stabilized by lipid phosphatase inhibitors, PIP2 antibodies9 potently inhibit each channel with a unique rate (GIRK1/4 (3-5) ≈ GIRK2 (ref. 6) ≫ IRK1 (ref. 10) ≈ ROMK (ref. 11)). Consistent with the faster dissociation of PIP2 from the GIRK channels, the carboxy terminus of GIRK1 binds 3H-PIP2 liposomes more weakly than does that of IRK1 or ROMK1. Mutation of a conserved arginine to glutamine at position 188 reduces the ability of ROMK1 to bind PIP2 and increases its sensitivity to inhibition by PIP2 antibodies. Interactions between GIRK channels and PIP2 are modulated by the βγ subunits of the G protein (Gβγ). When GIRK1/4 channels are allowed to run down completely, they are not activated by addition of Gβγ alone, but application of PIP2 activates them in minutes without Gβγ and in just seconds with Gβγ. Finally, coexpression of Gβγ with GIRK channels slows the inhibition of K+ currents by PIP2 antibodies by more than 10-fold. Thus Gβγ activates GIRK channels by stabilizing interactions between PIP2 and the K+ channel.
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Acknowledgements
We thank E. Phan for technical assistance; I. Bezprozvanny, C. Dessauer, D.Logothetis, C.-C. Lu, O. Moe, S. Muallem and H. Yin for discussions and advice; L. Jan for GIRK1 and ROMK1 antibodies; C. Dessauer and A. Gilman for Gαi1; P. Casey for Gβγ; and R. Alpern for support and encouragement. This work was supported by grants from the NKF of Texas (C.L.H.) and from the AHA and NIH (D.W.H.).
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Huang, CL., Feng, S. & Hilgemann, D. Direct activation of inward rectifier potassium channels by PIP2 and its stabilization by Gβγ. Nature 391, 803–806 (1998). https://doi.org/10.1038/35882
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DOI: https://doi.org/10.1038/35882
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