Interaction between the RGS domain of RGS4 with G protein alpha subunits mediates the voltage-dependent relaxation of the G protein-gated potassium channel.
1. In native cardiac myocytes, there is a time dependence to the G protein-gated inwardly rectifying K(+) (K(G)) channel current during voltage steps that accelerates as the concentration of acetylcholine is increased. This phenomenon has been called 'relaxation' and is not reproduced in the reconstituted Kir3.1/Kir3.4 channel in Xenopus oocytes. We have shown that RGS4, a regulator of G protein signalling, restores relaxation to the reconstituted Kir3.1/Kir3.4 channel. In this study, we examined the mechanism of this phenomenon by expressing various combinations of membrane receptors, G proteins, Kir3.0 subunits and mutants of RGS4 in Xenopus oocytes. 2. RGS4 restored relaxation to K(G) channels activated by the pertussis toxin (PTX)-sensitive G protein-coupled m(2)-muscarinic receptor but not to those activated by the G(s) protein-coupled beta(2)-adrenergic receptor. 3. RGS4 induced relaxation not only in heteromeric K(G) channels composed of Kir3.1 and Kir3.4 but also in homomeric assemblies of either an active mutant of Kir3.1 (Kir3.1/F137S) or an isoform of Kir3.2 (Kir3.2d). 4. Truncation mutants of RGS4 showed that the RGS domain itself was essential to reproduce the effect of wild-type RGS4 on the K(G) channel. 5. The mutation of residues in the RGS domain which interact with the alpha subunit of the G protein (G(alpha)) impaired the effect of RGS4. 6. This study therefore shows that interaction between the RGS domain and PTX-sensitive G(alpha) subunits mediates the effect of RGS4 on the agonist concentration-dependent relaxation of K(G) channels.
Inanobe
A
A
Department of Pharmacology II, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan.
Fujita
S
S
Makino
Y
Y
Matsushita
K
K
Ishii
M
M
Chachin
M
M
Kurachi
Y
Y
D000818:Animals; D004594:Electrophysiology; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D019204:GTP-Binding Proteins / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D017354:Point Mutation / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D017434:Protein Structure, Tertiary; D020710:RGS Proteins / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism; D013552:Swine; D014982:Xenopus laevis
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C497067:Kcnj3 protein, mouse; D015221:Potassium Channels; D020710:RGS Proteins; D011943:Receptors, Adrenergic, beta; D011976:Receptors, Muscarinic; C098799:RGS4 protein; D019204:GTP-Binding Proteins