Fig. 4

Histamine facilitates the maturation of cardiomyocytes derived from hiPSCs. a Sarcomeric structure analysis of hiPSC-CMs treated with histamine by α-actinin (red) and cTnI (green) staining on day 14 and day 30. Cell area was quantified on day 14, and the length-width ratio (L:W) was quantified on day 30. Scale bar 100 μM. b Representative co-immunostaining images of α-actinin (red) and CX43 (green) in hiPSC-CMs on the 14th day of histamine treatment. Scale bar 100 μM. c Representative transmission electron microscopy images of hiPSC-CMs on day18;white arrows indicate myofilament, and red dotted circles show cardiac mitochondria. d Gene expression of CASQ2, RYR2, and CALM1~3 of hiPSC-CMs. e Co-immunostaining of cTnI and EDU in hiPSC-CMs on day 14. Scale bar 100 μM. Data were quantified from 6 to 8 random fields in 3 assays. f The beating rates of hiPSC-CMs under the treatment of ISO. Data are expressed as the mean ± SEM. *p < 0.05, **p < 0.01 vs control (n = 3 for con group; n = 4 for his group)