title: Differential effects of genetically-encoded Gβγ scavengers on receptor-activated and basal Kir3.1/Kir3.4 channel current in rat atrial myocytes.
abstract: Opening of G-protein-activated inward-rectifying K(+) (GIRK, Kir3) channels is regulated by interaction with βγ-subunits of Pertussis-toxin-sensitive G proteins upon activation of appropriate GPCRs. In atrial and neuronal cells agonist-independent activity (I(basal)) contributes to the background K(+) conductance, important for stabilizing resting potential. Data obtained from the Kir3 signaling pathway reconstituted in Xenopus oocytes suggest that I(basal) requires free G(βγ). In cells with intrinsic expression of Kir3 channels this issue has been scarcely addressed experimentally. Two G(βγ)-binding proteins (myristoylated phosducin - mPhos - and G(αi1)) were expressed in atrial myocytes using adenoviral gene transfer, to interrupt G(βγ)-signaling. Agonist-induced and basal currents were recorded using whole cell voltage-clamp. Expression of mPhos and G(αi1) reduced activation of Kir3 current via muscarinic M(2) receptors (IK(ACh)). Inhibition of IK(ACh) by mPhos consisted of an irreversible component and an agonist-dependent reversible component. Reduction in density of IK(ACh) by overexpressed Gαi1, in contrast to mPhos, was paralleled by substantial slowing of activation, suggesting a reduction in density of functional M2 receptors, rather than G(βγ)-scavenging as underlying mechanism. In line with this notion, current density and activation kinetics were rescued by fusing the αi1-subunit to an Adenosine A(1) receptor. Neither mPhos nor G(αi1) had a significant effect on I(basal), defined by the inhibitory peptide tertiapin-Q. These data demonstrate that basal Kir3 current in a native environment is unrelated to G-protein signaling or agonist-independent free G(βγ). Moreover, our results illustrate the importance of physiological expression levels of the signaling components in shaping key parameters of the response to an agonist.
authors.affiliation: Institute of Physiology, Ruhr-University Bochum, D-44780 Bochum, Germany. Electronic address: cecile.kienitz@rub.de.
authors.forename: Marie-Cécile
authors.initials: MC
authors.lastname: Kienitz
authors.affiliation: Institute of Physiology, Ruhr-University Bochum, D-44780 Bochum, Germany.
authors.forename: Elisa
authors.initials: E
authors.lastname: Mintert-Jancke
authors.affiliation: Institute of Physiology, Ruhr-University Bochum, D-44780 Bochum, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Hertel
authors.affiliation: Institute of Physiology, Ruhr-University Bochum, D-44780 Bochum, Germany.
authors.forename: Lutz
authors.initials: L
authors.lastname: Pott
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials; D000818:Animals; D002478:Cells, Cultured; D018679:Cholinergic Agonists / Q000494:pharmacology; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000378:metabolism*; D020555:GTP-Binding Protein Regulators / Q000235:genetics* / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000235:genetics* / Q000378:metabolism; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism; D044388:GTP-Binding Protein gamma Subunits / Q000378:metabolism; D006325:Heart Atria / Q000166:cytology; D015640:Ion Channel Gating; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology*; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D043585:Receptor, Muscarinic M2 / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D018679:Cholinergic Agonists; D005136:Eye Proteins; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D020555:GTP-Binding Protein Regulators; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D010750:Phosphoproteins; D043585:Receptor, Muscarinic M2; C065631:phosducin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000109:Acetylcholine
keywords: Adenosine receptor; Cardiac myocyte; G protein; Kir3; Muscarinic receptor; Phosducin