Fig. 4. Impaired hypertrophic responses of MCK-Fktn-cKO (Fktn^flox/flox; MCK-Cre^+/−) cardiomyocytes.

a Representative immunofluorescence images of neonatal cardiomyocytes cultured with or without phenylephrine (PE) for 48 h (NCX1, green; phalloidin, red; DAPI, blue). Scale bar, 200 μm. b Magnified view of white squares in a. Scale bar, 50 μm. c Change in cell area of PE-treated cardiomyocytes (Pre, n = 106 cells; −PE, n = 98 cells; +PE, n = 96 cells from 10 hearts isolated from floxed mice. Pre, n = 59 cells; −PE, n = 87 cells; +PE, n = 113 cells from 10 hearts isolated from MCK-Fktn-cKO mice.). *P < 0.05 vs. cardiomyocytes before treatment with PE (Pre) isolated from floxed or MCK-Fktn-cKO mice and MCK-Fktn-cKO myocytes treated with or without PE; ^#P < 0.05 between indicated groups based on Tukey–Kramer tests. d Viability of cardiomyocytes from floxed or MCK-Fktn-cKO hearts. Confocal microscope images, LIVE/DEAD assays for myocytes cultured for 48 h. Scale bar, 100 μm. e Estimation of SR Ca²⁺ content (Pre-CM, n = 52 cells; Pre-FB, n = 13 cells; +PE-CM, n = 50 cells; +PE-FB, n = 26 cells from 10 hearts isolated from floxed mice. Pre-CM, n = 33 cells; Pre-FB, n = 46 cells; +PE-CM, n = 45 cells; +PE-FB, n = 23 cells from 10 hearts isolated from MCK-Fktn-cKO mice.). CM cardiomyocytes, FIB fibroblasts. *P < 0.05 vs. cardiomyocytes before treatment with PE (Pre) isolated from floxed mice; ^#P < 0.05 between indicated groups based on Tukey–Kramer tests.