Figure 9. Frailty scores grade the age‐related decline in peak contractions, Ca²⁺ transients, Ca²⁺ currents and gain when the pacing rate is increased to 4 Hz in voltage‐clamped myocytes.

A–D, peak contractions, Ca²⁺ transients, Ca²⁺ currents and the gain of SR Ca²⁺ release were graded by FI score when the pacing rate was increased from 2 to 4 Hz. Contractions (P = 0.005) and Ca²⁺ currents (P = 0.03) also declined with age at 4 Hz, whereas Ca²⁺ transients and gain did not (data not shown). Correlations were evaluated with linear regression analysis (n = 14–15 adult and 19–23 aged myocytes). Filled symbols indicate adult mice and open symbols indicate aged mice.