Protein kinase-independent inhibition of muscarinic K+ channels by staurosporine.
Acetylcholine (ACh) binding to atrial muscarinic receptors activates an inwardly rectifying K+ current (IK[ACh]) via a pertussis toxin-sensitive GTP-binding protein (GK). The muscarinic K+ channel (termed GIRK1) has been cloned, and the nucleotide sequence contains nine consensus sites for protein kinase C (PKC) phosphorylation (16). Dephosphorylation of the muscarinic K+ channel has been implicated in rapid IK[ACh] desensitization in the presence of agonist (13). Staurosporine is a widely used membrane-permeant inhibitor of PKC and other protein kinases (7), including G protein-coupled receptor kinases. We investigated the role of phosphorylation in the regulation of IK[ACh] by examining the effect of a variety of protein kinase inhibitors. Staurosporine produced a rapid and reversible dose-dependent decrease in IK[ACh], activated by either GTP or guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S). Other PKC inhibitors, including calphostin C and K-252b, were without effect on GTP gamma S-activated IK[ACh]. In excised patches of atrial membrane under nonphosphorylating conditions (0 ATP, 1 mM 5'-adenylylimidodiphosphate), staurosporine reversibly reduced muscarinic K+ channel activity without altering single-channel current amplitude. These results suggest that staurosporine inhibits IK[ACh] by a mechanism independent of intracellular protein kinases.
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Johns Hopkins University, School of Medicine, Department of Physiology, Baltimore, Maryland 21205.
Breitwieser
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GE
D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006325:Heart Atria; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D026902:Potassium Channel Blockers; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000502:physiology*; D011892:Rana catesbeiana; D011976:Receptors, Muscarinic / Q000378:metabolism*; D019311:Staurosporine
D000470:Alkaloids; D026902:Potassium Channel Blockers; D047428:Protein Kinase Inhibitors; D011976:Receptors, Muscarinic; D000266:Adenylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D011494:Protein Kinases; D019311:Staurosporine