RT Journal Article SR Electronic T1 Eudistomin D and Penaresin Derivatives as Modulators of Ryanodine Receptor Channels and Sarcoplasmic Reticulum Ca2+ ATPase in Striated Muscle JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 564 OP 575 DO 10.1124/mol.113.089342 VO 85 IS 4 A1 Paula L. Diaz-Sylvester A1 Maura Porta A1 Vanessa V. Juettner A1 Yuanzhao Lv A1 Sidney Fleischer A1 Julio A. Copello YR 2014 UL http://molpharm.aspetjournals.org/content/85/4/564.abstract AB Eudistomin D (EuD) and penaresin (Pen) derivatives are bioactive alkaloids from marine sponges found to induce Ca2+ release from striated muscle sarcoplasmic reticulum (SR). Although these alkaloids are believed to affect ryanodine receptor (RyR) gating in a “caffeine-like” manner, no single-channel study confirmed this assumption. Here, EuD and MBED (9-methyl-7-bromoeudistomin D) were contrasted against caffeine on their ability to modulate the SR Ca2+ loading/leak from cardiac and skeletal muscle SR microsomes as well as the function of RyRs in planar bilayers. The effects of these alkaloids on [3H]ryanodine binding and SR Ca2+ ATPase (SERCA) activity were also tested. MBED (1–5 μM) fully mimicked maximal activating effects of caffeine (20 mM) on SR Ca2+ leak. At the single-channel level, MBED mimicked the agonistic action of caffeine on cardiac RyR gating (i.e., stabilized long openings characteristic of “high-open-probability” mode). EuD was a partial agonist at the maximal doses tested. The tested Pen derivatives displayed mild to no agonism on RyRs, SR Ca2+ leak, or [3H]ryanodine binding studies. Unlike caffeine, EuD and some Pen derivatives significantly inhibited SERCA at concentrations required to modulate RyRs. Instead, MBED's affinity for RyRs (EC50 ∼0.5 μM) was much larger than for SERCA (IC50 > 285 μM). In conclusion, MBED is a potent RyR agonist and, potentially, a better choice than caffeine for microsomal and cell studies due to its reported lack of effects on adenosine receptors and phosphodiesterases. As a high-affinity caffeine-like probe, MBED could also help identify the caffeine-binding site in RyRs.