Abstract
CGP-37157 (CGP), a benzothiazepine derivative of clonazepam, is commonly utilized as a blocker of the mitochondrial Na+/Ca2+ exchanger. Yet, evidence suggests that CGP could also affect other targets, such as L-type Ca2+ channels and plasmalemma Na+/Ca2+ exchanger. Here, we tested the possibility of a direct modulation of ryanodine receptor channels (RyRs) and/or sarco/endoplasmic reticulum Ca2+ stimulated ATPase (SERCA) by CGP. In the presence of ruthenium red (inhibitor of RyRs), CGP decreased SERCA-mediated Ca2+ uptake of cardiac and skeletal sarcoplasmic reticulum (SR) microsomes (IC50's were 6.6 and 9.9 μM, respectively). The CGP effects on SERCA activity correlated with a decreased Vmax of ATPase activity of SERCA-enriched skeletal SR fractions. CGP (≥5 μM) also increased RyR-mediated Ca2+ leak from skeletal SR microsomes. Planar bilayer studies confirmed that both cardiac and skeletal RyRs are directly activated by CGP (EC50's = 9.4 and 12.0 μ, respectively). In summary, we found that CPG inhibits SERCA and activates RyR channels. Hence, the action of CGP on cellular Ca2+ homeostasis reported in the literature of cardiac, skeletal muscle as well as other non muscle systems requires further analysis to take into account the contribution of all CGP-sensitive Ca2+ transporters.
- Ion channel regulation
- Ion transporters (SERCA, Na/K ATPase, CFTR)
- Mitochondrial toxins
- Ischemia/Reperfusion
- Received July 20, 2010.
- Revision received September 30, 2010.
- Accepted October 4, 2010.
- The American Society for Pharmacology and Experimental Therapeutics