title: Ryanodine and an iodinated analog: doxorubicin effects on binding and Ca2+ accumulation in cardiac sarcoplasmic reticulum.
abstract: An 125I-iodinated ryanodine analog, modified by attaching an iodo-Cbz-beta-alanyl group to the C10eq hydroxy of ryanodine (iodo-carbobenzyloxy-beta-alanyl-ryanodine), binds to cardiac sarcoplasmic reticulum Ca2+ release channels with equal affinity as [3H]ryanodine. In the present study, both iodo-Cbz-beta-alanyl-ryanodine and ryanodine bound to canine cardiac microsomal membrane preparations in a Ca2+ dependent manner. At 10 microM free Ca2+ doxorubicin increased specific binding of both ligands, with doxorubicin concentrations of 4.06 +/- 0.44 and 6.22 +/- 1.31 microM inducing 50% maximal enhancement of binding for ryanodine and iodo-Cbz-beta-alanyl-ryanodine, respectively. Effects of ryanodine and iodo-Cbz-beta-alanyl-ryanodine +/- doxorubicin in vitro on cardiac sarcoplasmic reticulum Ca2+ release were compared indirectly by determining Ca2+ accumulation in cardiac microsomal vesicles loaded with 45Ca2+. In the absence of oxalate, neither ryanodine nor iodo-Cbz-beta-alanyl-ryanodine (10 microM) decreased net Ca2+ uptake, whereas doxorubicin reduced Ca2+ accumulation 20 +/- 2%. In the presence of oxalate and 0.4 microM free Ca2+ ("low"), both ryanodine and iodo-Cbz-beta-alanyl-ryanodine modestly decreased (by 19% and 17% at 10 nM, respectively) maximum Ca2+ accumulation. Increasing concentrations of ryanodine (100 nM-100 microM) and iodo-Cbz-beta-alanyl-ryanodine (100 nM-30 microM) had no greater effect, but 100 microM iodo-Cbz-beta-alanyl- ryanodine decreased net Ca2+ uptake 57 +/- 3%. Doxorubicin (30 microM) alone reduced Ca2+ uptake 36%; its effects with 1 nM-10 microM ryanodine or 1 nM-100 microM iodo-Cbz-beta-alanyl-ryanodine were additive.(ABSTRACT TRUNCATED AT 250 WORDS)
authors: Department of Cardiovascular Research, Lilly Research Laboratories, Eli Lilly Company, Indianapolis, IN 46285.
authors: N
authors: N
authors: Bowling
authors: D E
authors: DE
authors: Mais
authors: K
authors: K
authors: Gerzon
authors: A M
authors: AM
authors: Watanabe
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D004285:Dogs; D004317:Doxorubicin / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D008024:Ligands; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D011869:Radioligand Assay; D012433:Ryanodine / Q000031:analogs & derivatives* / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
chemical_list: C091220:3-iodobenzyloxycarbonyl-beta-alanylryanodine; D002132:Calcium Radioisotopes; D007457:Iodine Radioisotopes; D008024:Ligands; D012433:Ryanodine; D004317:Doxorubicin; D002118:Calcium