Fig. 6: Mechanical force assessment in the chamber-specific EHTs.

a A series of length increases of the EHTs is controlled by a highly sensitive motor. b, c Tracings depicting the measured EHT forces over time during sequential EHT stretching and field stimulation (b) and a high-magnitude example of the measured active force (c). d The active forces were measured and normalized to cross-sectional area (CSA), and then plotted as function of EHT length for both ventricular (blue) and atrial (red) EHTs. Note the typical length–tension relationships with the generated forces increasing for both tissue types as function of tissue length (n = 6, biologically independent samples). Also notice the significantly higher forces developing in the ventricular EHTs as compared with the atrial tissues. *p < 0.05, **p < 0.01, ****p < 0.0001, repeated-measurements two-way ANOVA followed by Sidak post hoc analysis. e Active forces developed by the ventricular and atrial EHTs with similar initial lengths (stimulated at 2 Hz and normalized per CSA). Note that the ventricular tissues developed significantly higher mean active force than the atrial tissues (n = 12, biologically independent samples). ****p < 0.0001, Mann–Whitney test. f, g Changes in contractile forces (normalized per CSA) in response to increasing calcium concentration for the ventricular (f) and atrial (g) EHTs (n = 4, biologically independent samples, for both EHT types). h–k Changes in contractile forces of the ventricular EHT following addition of 10 µM of isoproterenol (h, i) and 0.1 µM of nifedipine (j, k). Shown are the actual force tracings (h, j) and summary of the percentage change (i, k) in the mean measured forces of the atrial (red) and ventricular (blue) tissues in response to 10 µM of isoproterenol (n = 5, biologically independent samples, i) or 0.1 µM nifedipine (n = 5, biologically independent samples, k). All recordings were done at a stimulation frequency of 2 Hz. Values are expressed as mean ± SEM.