Colchicine inhibits acetylcholine receptor stimulation of G protein GTPase activity in rat striatum.
Colchicine, which is known to influence tubulin function, was used to delineate a possible role of tubulin in signal transduction in the rat striatal membranes. Low Km GTPase activity (EC 3.6.1.-) was assayed in 10 micrograms membrane protein using [gamma-32P]GTP at 37 degrees in an ATP-regenerating buffer containing 1 microM unlabeled GTP. At 10 and 100 microM, colchicine inhibited the GTPase activity by 18% and 40%, respectively. Colchicine (100 microM) inhibited the enzymatic activity by 30-40% at all the time points the reaction was monitored. Acetylcholine (ACh) stimulated the low Km GTPase activity in a concentration-dependent manner, by up to 57%. ACh-stimulated activity was accepted as reflecting GTP hydrolysis catalyzed by receptor-coupled transducer G proteins. In the presence of 100 microM colchicine, the ability of ACh to stimulate G protein GTPase activity was inhibited. For example, at 10 microM ACh the enzyme activity was stimulated up to 52%; in the presence of 100 microM colchicine, 10 microM ACh stimulated the activity by only up to 33%. These results suggest that colchicine disrupts ACh receptor-G protein coupling as a result of its interaction with tubulin or G protein(s) or both.
Ravindra
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Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta 30912.
Aronstam
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D000818:Animals; D018680:Cholinergic Antagonists; D003078:Colchicine / Q000494:pharmacology*; D003342:Corpus Striatum / Q000187:drug effects / Q000201:enzymology*; D020558:GTP Phosphohydrolases / Q000187:drug effects / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D008162:Lumicolchicines / Q000494:pharmacology; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011950:Receptors, Cholinergic / Q000502:physiology
D018680:Cholinergic Antagonists; D008162:Lumicolchicines; D011950:Receptors, Cholinergic; C042109:lumicolchicine; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D003078:Colchicine