Figure 5: Electromechanical properties of aging LV myocytes.

(a) Ca²⁺ transients of young (black traces) and old (blue traces) myocytes. Scale bars, 1 s, 0.25 F/F₀. Superimposed traces are reported in the inset. Scale bars, 250 ms, 0.25 F/F₀. (b) Quantitative data for Ca²⁺ transients obtained in myocytes from mice at 3 months (Young) and 29–30 months (Old) (Young, n=195 cells from 16 hearts; Old, n=131 cells from 11 hearts); data are shown as mean±s.e.m. and scatter plots. *P<0.05 versus Young (Mann–Whitney rank sum test). (c) Cell shortening of young (black traces) and old (blue traces) myocytes. Scale bars, 1 s, 1 μm. Superimposed traces are reported in the inset. Scale bars, 250 ms, 1 μm (d) Quantitative data for cell shortening properties obtained in myocytes from mice at 3 months (Young) and 29–30 months (Old) (Young, n=129 cells from 8 hearts; Old, n=117 cells from 7 hearts); data are shown as mean±s.e.m. and scatter plots. *P<0.05 versus Young (Mann–Whitney rank sum test). (e) AP profiles (upper traces) obtained from myocytes at different age (m, months) were applied as voltage-clamp command (AP-clamp) in an old myocyte to elicit Ca²⁺ transients (lower traces). Scale bars, 300 ms, 1 F/F₀, 40 mV. Ionic currents recorded are omitted. (f) Decay of Ca²⁺ transients elicited by five different AP-clamp protocols obtained in myocytes from male mice at 3–5 months (Young) and 28–33 months (Old) are shown as mean±s.e.m. (Young, n=12 cells from 5 hearts; Old, n=9 cells from 2 hearts). Levels of the Ca²⁺ fluorescence signal from the peak of the Ca²⁺ transient to 90% of the decay are reported. Data were fitted with mono-exponential functions (solid lines). Fitting parameters are reported in Supplementary Table 3. (g) Bivariate plot for APD50 of the AP used as V_clamp command and Ca²⁺ transient properties obtained from young and old myocytes reported in f. Data were fitted with linear regressions (dashed lines). Fitting parameters are reported in Supplementary Table 3.