TY - JOUR T1 - Eudistomin D and Penaresin Derivatives as Modulators of Ryanodine Receptor Channels and Sarcoplasmic Reticulum Ca<sup>2+</sup> ATPase in Striated Muscle JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.113.089342 SP - mol.113.089342 AU - Paula L. Diaz-Sylvester AU - Maura Porta AU - Vanessa V. Juettner AU - Yuanzhao Lv AU - Sidney Fleischer AU - Julio A. Copello Y1 - 2014/01/14 UR - http://molpharm.aspetjournals.org/content/early/2014/01/14/mol.113.089342.abstract N2 - 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 n-methylbromoeudistomin D (MBED) 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 sarcoplasmic reticulum 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 Po" 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 affinity for RyRs (EC50 ~ 0.5 μM) was much larger than for SERCA (IC50 &gt; 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. ER -