Abstract
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) 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 the open probability (Po) of very active (“high-activity”) RyR1 of SkM reconstituted into bilayers, but it had no effect on “low-activity” channels. Likewise, K201 activated cardiac RyR2 under systolic Ca2+ conditions (∼5 µM; channels at Po ∼0.3) but not under diastolic Ca2+ conditions (∼100 nM; Po < 0.01). Thus, K201-induced the 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 pathologic conditions, thus precluding abnormal RyR-mediated Ca2+ release.
Footnotes
- Received October 28, 2015.
- Accepted May 26, 2016.
This work was supported by the American Heart Association Midwest Affiliate [AHA-MWA 12180038] and the Eskridge Foundation.
- Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|