Fig. 5.

Morphogenetic strains measured during bending of the isolated heart. (a) Fluorescent labels were injected on the ventral (v) and dorsal (d) sides of the HT to measure longitudinal strains. (b) Longitudinal stretch ratios (${\lambda }_{zv}\hspace{1em}>\hspace{1em}1,{\lambda }_{zd}\hspace{1em}<\hspace{1em}1$) indicate ventral elongation and dorsal shortening in both control hearts and hearts treated with 30 μM blebbistatin (Bleb). Linear regressions (solid lines) suggest longitudinal stretch ratios change linearly with time (for control and Bleb-treated hearts, R ²= 0.9839, 0.9157 for ${\lambda }_{zv}$ and R ²= 0.7831, 0.8409 for ${\lambda }_{zd}$, respectively). (c) Summary of all myocardial stretch ratios after 24 h culture: radial ${\lambda }_r$, circumferential ${\lambda }_{\theta }$, longitudinal on the ventral side ${\lambda }_{zv}$, and longitudinal on the dorsal side ${\lambda }_{zd}$. The myocardial wall thickened less in Bleb-treated hearts than that in control, and even less in hearts treated with 100 nM cytochalasin D (CytoD; ${\hspace{0.17em}}^{*}p\hspace{1em}<\hspace{1em}0.001$, one-way ANOVA). Note that longitudinal stretch ratios were not measured in CytoD-treated hearts, where bending was inhibited. Scale bar: 200 μm.