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Calcium-sensing receptors regulate cardiomyocyte Ca2+ signaling via the sarcoplasmic reticulum-mitochondrion interface during hypoxia/reoxygenation

Fang-hao Lu1, Zhiliang Tian2, Wei-hua Zhang15*, Ya-jun Zhao1, Hu-lun Li3, Huan Ren4, Hui-shuang Zheng1, Chong Liu1, Guang-xia Hu1, Ye Tian1, Bao-feng Yang5, Rui Wang6 and Chang-qing Xu15*

Author Affiliations

1 Department of Pathophysiology, Harbin Medical University, Harbin 150086, China

2 Department of Pediatrics, the second affiliated Hospital of Harbin Medical University, Harbin 150086, China

3 Department of Neurobiology, Harbin Medical University, Harbin 150086, China

4 Department of Immunology, Harbin Medical University, Harbin 150086, China

5 Bio-pharmaceutical Key Laboratory of Heilongjiang Province, Harbin Medical University, Harbin 150086, China

6 Department of Biology, Lakehead University, Thunder Bay, Ontario, P7B5E1, Canada

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Journal of Biomedical Science 2010, 17:50  doi:10.1186/1423-0127-17-50

Published: 17 June 2010

Abstract

Communication between the SR (sarcoplasmic reticulum, SR) and mitochondria is important for cell survival and apoptosis. The SR supplies Ca2+ directly to mitochondria via inositol 1,4,5-trisphosphate receptors (IP3Rs) at close contacts between the two organelles referred to as mitochondrion-associated ER membrane (MAM). Although it has been demonstrated that CaR (calcium sensing receptor) activation is involved in intracellular calcium overload during hypoxia/reoxygenation (H/Re), the role of CaR activation in the cardiomyocyte apoptotic pathway remains unclear. We postulated that CaR activation plays a role in the regulation of SR-mitochondrial inter-organelle Ca2+ signaling, causing apoptosis during H/Re. To investigate the above hypothesis, cultured cardiomyocytes were subjected to H/Re. We examined the distribution of IP3Rs in cardiomyocytes via immunofluorescence and Western blotting and found that type 3 IP3Rs were located in the SR. [Ca2+]i, [Ca2+]m and [Ca2+]SR were determined using Fluo-4, x-rhod-1 and Fluo 5N, respectively, and the mitochondrial membrane potential was detected with JC-1 during reoxygenation using laser confocal microscopy. We found that activation of CaR reduced [Ca2+]SR, increased [Ca2+]i and [Ca2+]m and decreased the mitochondrial membrane potential during reoxygenation. We found that the activation of CaR caused the cleavage of BAP31, thus generating the pro-apoptotic p20 fragment, which induced the release of cytochrome c from mitochondria and the translocation of bak/bax to mitochondria. Taken together, these results reveal that CaR activation causes Ca2+ release from the SR into the mitochondria through IP3Rs and induces cardiomyocyte apoptosis during hypoxia/reoxygenation.