Figure 4.

Measurement and comparison of inotropic response to CaCl₂ and isoproterenol in engineered and adult rat myocardium. (a) Example stress trace from MTF contractility measurements illustrating the Calcium chloride (CaCl₂) concentration response protocol used to compare the inotropic response profiles of engineered and adult rat myocardium. CaCl₂ was administered cumulatively over 5 min intervals to achieve bath concentrations ranging from 0.05 to 10 mM, and contractile stress measurements were recorded at each concentration. (b) Percent change from baseline contractile response profile of ventricular muscle strips isolated from adult rats (Adult Heart) to increasing CaCl₂ concentration, EC₅₀ = 3 mM, n = 6 muscle strips. (c) Percent change from baseline contractile response profile of engineered myocardium comprised of neonate rat cardiac myocytes cultured on 15 µm wide FN lines spaced 15 µm apart (In Vitro Lines) to increasing CaCl₂ concentration, EC₅₀ = 7 mM, n = 9 MTFs, #chips = 2. (d) Percent change from baseline contractile response profile of engineered myocardium comprised of neonate rat cardiac myocytes cultured on 15 µm wide FN lines spaced 2 µm apart (In Vitro Aniso) to increasing CaCl₂ concentration, EC₅₀ = 5 nM, n = 15 MTFs, #chips = 3. (e) Example stress trace from MTF contractility measurements illustrating the Isoproterenol (Iso) concentration–response protocol used to compare the inotropic response profiles of engineered and adult rat myocardium. Baseline contractile stress measurements were recorded for 10 min, then Iso concentrations ranging from 10⁻¹⁰ to 10⁻⁴ M were administered in 5 min intervals and recordings of contractile force were taken for each muscle construct. (f) Percent change from baseline contractile response profile of ventricular muscle strips isolated from adult rats (Adult Heart) to isoproterenol exposure, EC₅₀ = 35 nM, n = 4 muscle strips. (g) Percent change from baseline contractile response profile of engineered myocardium comprised of neonate rat cardiac myocytes cultured on 15 µm wide FN lines spaced 15 µm apart (In Vitro Lines) to isoproterenol exposure, EC₅₀ = 200 nM, n = 13 MTFs, #chips = 4. (h) Percent change from baseline contractile response profile of engineered myocardium comprised of neonate rat cardiac myocytes cultured on 15 µm wide FN lines spaced 2 µm apart (In Vitro Aniso) to Iso exposure, EC₅₀ = 143 nM, n = 15 MTFs, #chips = 4. * = P < 0.05 versus baseline, ** = P < 0.001 versus baseline. Data presented as mean ± SEM