PT  - JOURNAL ARTICLE
AU  - Yuanzhao L Darcy
AU  - Paula L Diaz-Sylvester
AU  - Julio A Copello
TI  - K201 (JTV519) is a Ca&lt;sup&gt;2+&lt;/sup&gt; dependent blocker of SERCA and a partial agonist of   ryanodine receptors in striated muscle
AID  - 10.1124/mol.115.102277
DP  - 2016 Jan 01
TA  - Molecular Pharmacology
PG  - mol.115.102277
4099  - http://molpharm.aspetjournals.org/content/early/2016/05/27/mol.115.102277.short
4100  - http://molpharm.aspetjournals.org/content/early/2016/05/27/mol.115.102277.full
AB  - K201 (JTV-519) may prevent abnormal Ca2+ leak from the sarcoplasmic reticulum (SR) in the ischemic heart and skeletal muscle (SkM) by stabilizing the ryanodine receptors (RyRs; RyR1 and RyR2 respectively). We tested direct modulation of the SR Ca2+-stimulated ATPase (SERCA) and RyRs by K201. In isolated cardiac and SkM SR microsomes, K201 slowed the rate of SR Ca2+ loading, suggesting potential SERCA block and/or RyR agonism. K201 displayed Ca2+ dependent inhibition of SERCA-dependent ATPase activity, which was measured in microsomes incubated with 200, 2 and 0.25 μM Ca2+, and with the half-maximal K201 inhibitory doses (IC50&#039;-s) estimated at 130, 19 and 9 μM (cardiac muscle) and 104, 13 and 5 μM (SkM SR). K201 (≥ 5 μM) increased RyR1-mediated Ca2+ release from SkM microsomes. Maximal K201 doses at 80 μM produced ~ 37% of the increase in SkM SR Ca2+ release observed with the RyR agonist caffeine. K201 (≥ 5 μM) increased open probability (Po) of very active (&quot;high-activity&quot;) RyR1 of SkM reconstituted into bilayers but had no effect on &quot;low activity&quot; channels. Likewise, K201 activated cardiac RyR2 under systolic Ca2+ conditions (~5 μM; channels at Po ~ 0.3) but not under diastolic Ca2+ condition (~100 nM; Po &amp;lt; 0.01). Thus, K201-induced inhibition of SR Ca2+ leak found in cell-system studies may relate to potentially potent SERCA block under resting Ca2+ conditions. SERCA block likely produces mild SR depletion in normal conditions but could prevent SR Ca2+ overload under pathological conditions, then, precluding abnormal RyR-mediated Ca2+ release.