Inhibition of an inwardly rectifying K+ channel by G-protein alpha-subunits.
Cholinergic muscarinic, serotonergic, opioid and several other G-protein- coupled neurotransmitter receptors activate inwardly rectifying K+ channels of the GIRK family, slowing the heartbeat and decreasing the excitability of neuronal cells. Inhibitory modulation of GIRKs by G-protein-coupled receptors may have important implications in cardiac and brain physiology. Previously G alpha and G beta gamma subunits of heterotrimeric G proteins have both been implicated in channel opening, but recent studies attribute this role primarily to the G beta gamma dimer that activates GIRKs in a membrane-delimited fashion, probably by direct binding to the channel protein. We report here that free GTP gamma S-activated G alpha i 1, but not G alpha i 2 or G alpha i 3, potently inhibits G beta 1 gamma 2- induced GIRK activity in excised membrane patches of Xenopus oocytes expressing GIRK1. High-affinity but partial inhibition is produced by G alpha s-GTP gamma S. G alpha i 1-GTP gamma S also inhibits G beta 1 gamma 2- activated GIRK in atrial myocytes. Antagonistic interactions between G alpha and G beta gamma may be among the mechanisms determining specificity of G protein coupling to GIRKs.[1]References
- Inhibition of an inwardly rectifying K+ channel by G-protein alpha-subunits. Schreibmayer, W., Dessauer, C.W., Vorobiov, D., Gilman, A.G., Lester, H.A., Davidson, N., Dascal, N. Nature (1996) [Pubmed]
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