Aims: Rapamycin (sirolimus) is an antibiotic that inhibits protein synthesis through mammalian targeting of rapamycin (mTOR) signaling, and is used as an immunosuppressant in the treatment of organ rejection in transplant recipients. Rapamycin confers preconditioning-like protection against ischemic-reperfusion injury in isolated mouse heart cultures. Our aim was to further define the role of rapamycin in intracellular Ca2+ homeostasis and to investigate the mechanism by which rapamycin protects cardiomyocytes from hypoxic damage. Main methods: We demonstrate here that rapamycin protects rat heart cultures from hypoxic-reoxygenation (H/R) damage, as revealed by assays of lactate dehydrogenase (LDH) and creatine kinase (CK) leakage to the medium, by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5- diphenyltetrazolium bromide) measurements, and desmin immunostaining. As a result of hypoxia, intracellular calcium levels ([Ca2+]i) were elevated. However, treatment of heart cultures with rapamycin during hypoxia attenuated the increase of [Ca2+]i. Rapamycin also attenuated 45Ca2+ uptake into the sarcoplasmic reticulum (SR) of skinned heart cultures in a dose- and time-dependent manner. KB-R7943, which inhibits the "reverse" mode of Na+/Ca2+ exchanger (NCX), protected heart cultures from H/R damage with or without the addition of rapamycin. Rapamycin decreased [Ca2+]i following its elevation by extracellular Ca2+ ([Ca2+] o) influx, thapsigargin treatment, or depolarization with KCl. Key findings: We suggest that rapamycin induces cardioprotection against hypoxic/reoxygenation damage in primary heart cultures by stimulating NCX to extrude Ca2+ outside the cardiomyocytes. Significance: According to our findings, rapamycin preserves Ca2+ homeostasis and prevents Ca2+ overload via extrusion of Ca2+ surplus outside the sarcolemma, thereby protecting the cells from hypoxic stress.
|Number of pages||8|
|State||Published - 4 Jul 2011|
Bibliographical noteFunding Information:
We thank A. Isak for technical support. We also thank Sharon Victor for helping to prepare this manuscript for publication. This work was supported in part by an ISF grant no. 876/05 and through the generous support of the Adar Program for the Advancement of Research in Heart Function at Bar-Ilan University . The sponsors were not involved in any way in the making of this paper or the decision to submit it for publication.
- Heart cultures
- Hypoxia reoxygenation
- Intracellular calcium
- Rapamycin (sirolimus)
- SR Ca ATPase (SERCA2a)
- Sodium calcium exchanger (NCX)