title: 4,6-Dibromo-3-hydroxycarbazole (an analogue of caffeine-like Ca2+ releaser), a novel type of inhibitor of Ca(2+)-induced Ca2+ release in skeletal muscle sarcoplasmic reticulum.
abstract: 1. 4,6-Dibromo-3-hydroxycarbazole (DBHC) was synthesized as an analogue of bromoeudistomin D (BED), a powerful Ca2+ releaser, and its pharmacological properties were examined. 2. In Ca2+ electrode experiments, DBHC (100 microM) markedly inhibited Ca2+ release from the heavy fraction of sarcoplasmic reticulum (HSR) induced by caffeine (1 mM) and BED (10 microM). 3. DBHC (0.1 to 100 microM) inhibited 45Ca2+ release induced by Ca2+ from HSR in a concentration-dependent manner. 4. DBHC (100 microM) abolished 45Ca2+ release induced by caffeine (1 mM) and BED (10 microM) in HSR. 5. Inhibitory effects of calcium-induced calcium release (CICR) blockers such as procaine, ruthenium red and Mg2+ on 45Ca2+ release were clearly observed at Ca2+ concentrations from pCa 7 to pCa 5.5, and were decreased at Ca2+ concentrations higher than pCa 5.5 or lower than pCa 7. However, DBHC decreased Ca2+ release induced by Ca2+ over the wide range of extravesicular Ca2+ concentrations. 6. [3H]-ryanodine binding to HSR was suppressed by ruthenium red, Mg2+ and procaine, but was not affected by DBHC up to 100 microM. 7. [3H]-ryanodine binding to HSR was enhanced by caffeine and BED. DBHC antagonized the enhancement in a concentration-dependent manner. 8. 9-[3H]-Methyl-7-bromo-eudistomin D, an 3H-labelled analogue of BED, specifically bound to HSR. Both DBHC and caffeine increased the KD value without affecting the Bmax value, indicating a competitive mode of inhibition. 9. These results suggest that DBHC binds to the caffeine binding site to block Ca2+ release from HSR. This drug is a novel type of inhibitor for the CICR channels in SR and may provide a useful tool for clarifying the Ca2+ releasing mechanisms in SR.
authors.affiliation: Department of Pharmaceutical Molecular Biology, Tohoku University, Sendai, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Takahashi
authors.forename: K
authors.initials: K
authors.lastname: Furukawa
authors.forename: D
authors.initials: D
authors.lastname: Kozutsumi
authors.forename: M
authors.initials: M
authors.lastname: Ishibashi
authors.forename: J
authors.initials: J
authors.lastname: Kobayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Ohizumi
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002227:Carbazoles / Q000494:pharmacology*; D002243:Carbolines / Q000494:pharmacology; D066298:In Vitro Techniques; D017736:Ion-Selective Electrodes; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D011343:Procaine / Q000494:pharmacology; D011817:Rabbits; D012430:Ruthenium Red / Q000494:pharmacology; D012433:Ryanodine; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
chemical_list: C094081:4,6-dibromo-3-hydroxycarbazole; D002132:Calcium Radioisotopes; D002227:Carbazoles; D002243:Carbolines; C048237:7-bromoeudistomine D; D012430:Ruthenium Red; C060741:9-methyl-7-bromoeudistomin D; D012433:Ryanodine; D002110:Caffeine; D011343:Procaine; D008274:Magnesium; D002118:Calcium