title: Calcium homeostasis in human induced pluripotent stem cell-derived cardiomyocytes.
abstract: BACKGROUND
  Cardiomyocytes generated from human induced pluripotent stem cells (hiPSCs) are suggested as the most promising candidate to replenish cardiomyocyte loss in regenerative medicine. Little is known about their calcium homeostasis, the key process underlying excitation-contraction coupling.
  
  
  OBJECTIVE
  We investigated the calcium handling properties of hiPSC-derived cardiomyocytes and compared with those from human embryonic stem cells (hESCs).
  
  
  RESULTS
  We differentiated cardiomyocytes from hiPSCs (IMR90 and KS1) and hESCs (H7 and HES3) with established protocols. Beating outgrowths from embryoid bodies were typically observed 2 weeks after induction. Cells in these outgrowths were stained positively for tropomyosin and sarcomeric alpha-actinin. Reverse-transcription polymerase chain reaction studies demonstrated the expressions of cardiac-specific markers in both hiPSC- and hESC-derived cardiomyocytes. Calcium handling properties of 20-day-old hiPSC- and hESC-derived cardiomyocytes were investigated using fluorescence confocal microscopy. Compared with hESC-derived cardiomyocytes, spontaneous calcium transients from both lines of hiPSC-derived cardiomyocytes were of significantly smaller amplitude and with slower maximal upstroke velocity. Better caffeine-induced calcium handling kinetics in hESC-CMs indicates a higher sacroplasmic recticulum calcium store. Furthermore, in contrast with hESC-derived cardiomyocytes, ryanodine did not reduce the amplitudes, maximal upstroke and decay velocity of calcium transients of hiPSC-derived cardiomyocytes. In addition, spatial inhomogeneity in temporal properties of calcium transients across the width of cardiomyocytes was more pronounced in hiPSC-derived cardiomyocytes than their hESC counterpart as revealed line-scan calcium imaging. Expressions of the key calcium-handling proteins including ryanodine recptor-2 (RyR2), sacroplasmic recticulum calcium-ATPase (SERCA), junction (Jun) and triadin (TRDN), were significantly lower in hiPSC than in hESCs.
  
  
  CONCLUSIONS
  The results indicate the calcium handling properties of hiPSC-derived cardiomyocytes are relatively immature to hESC counterparts.
authors: Cardiology Division, Department of Medicine, Queen Mary Hospital, University of Hong Kong, Hong Kong, China.
authors: Yee-Ki
authors: YK
authors: Lee
authors: Kwong-Man
authors: KM
authors: Ng
authors: Wing-Hon
authors: WH
authors: Lai
authors: Yau-Chi
authors: YC
authors: Chan
authors: Yee-Man
authors: YM
authors: Lau
authors: Qizhou
authors: Q
authors: Lian
authors: Hung-Fat
authors: HF
authors: Tse
authors: Chung-Wah
authors: CW
authors: Siu
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