Calcium-sensing receptors regulate cardiomyocyte Ca2+ signaling via the sarcoplasmic reticulum-mitochondrion interface during hypoxia/reoxygenation.
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.
Lu
Fang-hao
FH
Department of Pathophysiology, Harbin Medical University, Harbin 150086, China.
Tian
Zhiliang
Z
Zhang
Wei-hua
WH
Zhao
Ya-jun
YJ
Li
Hu-lun
HL
Ren
Huan
H
Zheng
Hui-shuang
HS
Liu
Chong
C
Hu
Guang-xia
GX
Tian
Ye
Y
Yang
Bao-feng
BF
Wang
Rui
R
Xu
Chang-qing
CQ
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D015153:Blotting, Western; D002122:Calcium Chloride / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology*; D015687:Cell Hypoxia / Q000502:physiology; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D005682:Gadolinium / Q000494:pharmacology; D007150:Immunohistochemistry; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000502:physiology; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism*; D051381:Rats; D044169:Receptors, Calcium-Sensing / Q000819:agonists / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D053496:Inositol 1,4,5-Trisphosphate Receptors; D044169:Receptors, Calcium-Sensing; D005682:Gadolinium; D002122:Calcium Chloride; C038958:gadolinium chloride; D010100:Oxygen