Figure 1.

Passive stiffness and Ca²⁺ activated force in “permeabilized” cardiac myocytes from patients with repair of tetralogy of Fallot undergoing pulmonary valve replacement (rToF‐PVR) are similar to those from right ventricle (RV) donors. A, A typical force trace showing activation of a single myocyte by an increase in solution Ca²⁺ and the measurement of Ca²⁺‐activated force and crossbridge kinetics (k _tr). For (B, C, D, and F), each small symbol shows the result from 1 myocyte, and each large symbol shows the mean derived from replicate myocytes from each donor or patient. The horizontal bars show the overall mean±SD, calculated using each mean value derived from replicate myocytes (large symbols) as a single datum for the statistical analysis. B, Passive force, measured as the difference between passive forces at sarcomere lengths 2.0 and 2.3 µm. There were 19 RV donor myocytes (1–6 myocytes from each of 7 donors used in this panel) and 16 rToF‐PVR myocytes (1–4 myocytes from each of 6 patients with rToF undergoing PVR used in this panel). C, Maximum Ca²⁺‐activated force, corrected for myocyte cross‐sectional area. There were 23 donor myocytes (1–6 myocytes from each of 7 donors) and 19 rToF‐PVR myocytes (1–4 myocytes from each of 7 patients). D, Rate of redevelopment of force (k _tr) after a release/restretch protocol at maximum Ca²⁺. There were 21 donor myocytes (1–6 myocytes from each of 7 donors) and 19 rToF‐PVR myocytes (1–4 myocytes from each of 7 patients). E, Force–Ca²⁺ relationship. All forces are expressed relative to the maximum force at 30 µmol/L Ca²⁺. In this panel, the symbols show overall mean±SD for each [Ca²⁺]. There were 1 to 6 myocytes from each of 5 donors and 1 to 4 myocytes from each of 7 patients. F, Ca²⁺ sensitivity, expressed as the pCa50 value (−log₁₀ of [Ca²⁺] required for 50% activation of force), and serves as a summary variable for the same data as in (E). Statistical analysis showed no significant differences (P>0.05, unpaired t tests) between the overall mean data for RV donor and patients with rToF undergoing PVR for any of the measured parameters.