Properties of the binding sites of [3H]9-methyl-7-bromoeudistomin D in bovine aortic smooth muscle microsomes.
[3H]9-Methyl-7-bromoeudistomin D ([3H]MBED), a powerful caffeine-like Ca2+ releaser, binds to the caffeine binding site of terminal cisternae of skeletal muscle sarcoplasmic reticulum and activates Ca(2+)-induced Ca2+ release. Properties of the binding site of [3H]MBED were investigated in aortic smooth muscle. The specific activity was higher in microsomes than in other fractions. [3H]MBED binding sites in smooth muscle microsomes were of a single class with a high affinity (KD 50nM), comparable with that in skeletal muscle sarcoplasmic reticulum. Caffeine competitively inhibited [3H]MBED binding, indicating MBED shares the same binding site with caffeine. Solubilization and fractionation of the microsomes gave two fractions of [3H]MBED binding activities. These results suggest that, in smooth muscle, there are multiple binding sites of [3H]MBED and caffeine, which might correspond to different pharmacological actions of caffeine on smooth muscle. Therefore, [3H]MBED, which binds to the different binding sites of caffeine, is useful as a probe for investigation of the actions of caffeine at the molecular level.
Department of Pharmaceutical Molecular Biology, Tohoku University, Sendai, Japan.
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M
Adachi
Y
Y
Fang
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Yamakuni
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Kobayashi
Y
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Ohizumi
D000818:Animals; D001011:Aorta; D001665:Binding Sites; D001667:Binding, Competitive / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002243:Carbolines / Q000378:metabolism*; D002417:Cattle; D008861:Microsomes / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*
D002243:Carbolines; C060741:9-methyl-7-bromoeudistomin D; D002110:Caffeine