title: Characteristics of 45Ca2+ release induced by quinolidomicin A1, a 60-membered macrolide from skeletal muscle sarcoplasmic reticulum.
abstract: Quinolidomicin A1, a 60-membered macrolide purified from an actinomycete Micromonospora sp. markedly induced 45Ca2+ release from the heavy fraction of skeletal muscle sarcoplasmic reticulum (HSR), but induced only slightly from the light fraction of sarcoplasmic reticulum (LSR), showing a lack of the ionophoretic activity even at a high concentration (300 microM). This was also confirmed by measuring the 45Ca2+ transport activity of quinolidomicin A1 across an organic solvent barrier. Quinolidomicin A1 (3-300 microM) increased 45Ca2+ release from HSR with an EC50 value of approx. 20 microM. The potency of quinolidomicin A1 was approx. 100-fold higher than that of caffeine. The bell-shaped profile of Ca2+ dependence for quinolidomicin A1 was different from that for caffeine. Blockers of Ca2+ release channels such as Mg2+ (10 mM), procaine (10 mM) and ruthenium red (10 microM) partially blocked quinolidomicin A1 (30 microM)-induced 45Ca2+ release from HSR. At 0 degrees C, quinolidomicin A1-induced 45Ca2+ release was ascertained not to be due to the inhibition of Ca2+ ATPase by the ATPase assay. Quinolidomicin A1 potentiated [3H]ryanodine binding to HSR with a decrease in KD but without a change in Bmax. These results suggest that quinolidomicin A1-induced Ca2+ release from HSR is consisted of two components, which are both sensitive and insensitive to blockers of Ca2+ release channels, and that the former component is associated with the ryanodine receptor.
authors.affiliation: Department of Pharmaceutical Molecular Biology, Faculty of Pharmaceutical Sciences, Tohoku University, Sendai, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Ohkura
authors.forename: Y
authors.initials: Y
authors.lastname: Miyashita
authors.forename: M
authors.initials: M
authors.lastname: Kakubari
authors.forename: Y
authors.initials: Y
authors.lastname: Hayakawa
authors.forename: H
authors.initials: H
authors.lastname: Seto
authors.forename: Y
authors.initials: Y
authors.lastname: Ohizumi
mesh_terms: D000192:Actinomycetales; D000704:Analysis of Variance; D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D007700:Kinetics; D018942:Macrolides; D015394:Molecular Structure; D018482:Muscle, Skeletal / Q000378:metabolism*; D011817:Rabbits; D012433:Ryanodine / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D000903:Antibiotics, Antineoplastic; D002132:Calcium Radioisotopes; D018942:Macrolides; C084378:quinolidomicin A1; D012433:Ryanodine; D002110:Caffeine; D002118:Calcium