Neuron
Volume 16, Issue 2, February 1996, Pages 423-429
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Article
Cloning of a Xenopus laevis Inwardly Rectifying K+ Channel Subunit That Permits GIRK1 Expression of IKACh Currents in Oocytes

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Abstract

Xenopus oocytes injected with GIRK1 mRNA express inwardly rectifying K+ channels resembling IKACh. Yet IKACh, the atrial G protein–regulated ion channel, is a heteromultimer of GIRK1 and CIR. Reasoning that an oocyte protein might be substituting for CIR, we cloned XIR, a CIR homolog endogenously expressed by Xenopus oocytes. Coinjecting XIR and GIRK1 mRNAs produced large, inwardly rectifying K+ currents responsive to m2-muscarinic receptor stimulation. The m2-stimulated currents of oocytes expressing GIRK1 alone decreased 80% after injecting antisense oligonucleotides specific to the 5′ untranslated region of XIR, but GIRK1/CIR currents were unaffected. Thus, GIRK1 without XIR or CIR only ineffectively produces currents in oocytes. This result suggests that GIRK1 does not form native homomultimeric channels.

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