Tissue- and subcellular-distribution of the binding site of [3H]9-methyl-7-bromoeudistomin D,a potent caffeine-like Ca2+ releaser,in rabbits

Abstract— Tissue and subcellular distribution of the binding site of ³H-labelled 9-methyl-7-bromoeudistomin D ([³H]MBED), a powerful caffeine-like Ca²⁺ releaser, were investigated in rabbits. The order of specific activities of total homogenates was liver > brain > other tissues. All binding was completely suppressed by 10 Mm caffeine, indicating that all [³H]MBED binding sites are modulated by caffeine. [³H]MBED binding sites distributed mainly in membrane fractions rather than soluble fractions in most tissues. In lung and liver, [³H]MBED binding was enriched in microsomes. [³H]MBED may be useful as a probe to investigate the actions of caffeine at the molecular level not only in muscles but also in a variety of tissues including liver, kidney and lung.