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. 2018 Jan 19;8:1111. doi: 10.3389/fphys.2017.01111

Figure 1.

Figure 1

(A) Contractile function of myofibrils of a single demembranated human stem cell-derived cardiomyocyte (d-hESC-CM) (A1) and contractile function of a single bundle of adult human ventricular myofibrils (hvMFs) (A2) were investigated using the same micromechanical setup and experimental conditions. Microphotographs (A1,A2) were taken in bright field (BF). (B) A single elongated d-hESC-CM immunostained against α-actinin was observed in phase contrast (PhC; B1), fluorescence (FL; B2), or simultaneously in PhC and FL (B3). Note the predominant axial alignment of myofibrils within d-hESC-CMs (A1,B1−3). (C) Representative force transients of a single d-hESC-CM (black trace; d-hESC-CMs shown in A1 and Video 3) and of a hvMFs-bundle (gray trace; hvMFs-bundle shown in A2 and Video 4) mounted and held isometrically between the tips of a stiff needle (left) and a nN-sensitive force probe (right). Isometric active (FACT) at saturating [Ca2+] (pCa 4.18) and passive (Fpass) forces, rate constant kACT of Ca2+-induced force development, rate constant kTR of force re-development and the three kinetic parameters (kLIN, tLIN, kREL) characterizing force relaxation upon rapid Ca2+-removal (detailed in the right panel) are indicated for this d-hESC-CM (T = 15°C, pCa 4.18): FACT = 43 kPa, Fpass = 7 kPa, kACT = 0.60 s−1, kTR = 0.65 s−1, kLIN = 0.30 s−1, tLIN = 243 ms, kREL = 4.2 s−1; and for the single hvMF-bundle: FACT = 72 kPa, Fpass = 9 kPa, kACT = 0.50 s−1, kTR = 0.56 s−1, kLIN = 0.23 s−1, tLIN = 216 ms, kREL = 5.3 s−1. (D) d-hESC-CM (indicated by arrow in D1) immunostained solely against αMyHC isoform and exhibiting no sarcomeric fluorescence (i.e., βMyHC-positive d-hESC-CM; D2) was micromechanically investigated (D3). Force parameters from several immunostained d-hESC-CMs are given in Table 1. Images were taken in PhC (D1), FL (D2), or BF (D3). All scale bars = 10 μm.