M. Adachi et al., PROPERTIES OF THE BINDING-SITES OF [H-3] 9-METHYL-7-BROMOEUDISTOMIN-DIN BOVINE AORTIC SMOOTH-MUSCLE MICROSOMES, Journal of Pharmacy and Pharmacology, 46(9), 1994, pp. 771-773
[H-3]9-Methyl-7-bromoeudistomin D ([H-3]MBED), a powerful caffeine-lik
e Ca2+ releaser, binds to the caffeine binding site of terminal cister
nae of skeletal muscle sarcoplasmic reticulum and activates Ca2+-induc
ed Ca2+ release. Properties of the binding site of [H-3]MBED were inve
stigated in aortic smooth muscle. The specific activity was higher in
microsomes than in other fractions. [H-3]MBED binding sites in smooth
muscle microsomes were of a single class with a high affinity (K-D 50
nm), comparable with that in skeletal muscle sarcoplasmic reticulum. C
affeine competitively inhibited [H-3]MBED binding, indicating MBED sha
res the same binding site with caffeine. Solubilization and fractionat
ion of the microsomes gave two fractions of [H-3]MBED binding activiti
es. These results suggest that, in smooth muscle, there are multiple b
inding sites of [H-3]MBED and caffeine, which might correspond to diff
erent pharmacological actions of caffeine on smooth muscle. Therefore,
[H-3]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.