Figure 2.
Impaired steady-state isometric active stress production in trabeculae from rats with cardiac hypertrophy. (A) Exemplar recordings from a trabecula show simultaneous measurement of length, stress, and heat rate during the isometric length-change protocol. The isometric length-change protocol involved a series of 3-Hz isometric contractions at progressively diminishing muscle lengths, commencing at Lo and proceeding to the minimum length (around 0.77 Lo), which produced near-zero developed stress. A single twitch at steady-state is shown in each inset. Baseline heat rate is indicated by the horizontal broken line. (B) Average total and passive stress-length relations of control (solid lines) and hypertrophic rat (broken lines) trabeculae, n = 12. Data from an exemplar trabecula are shown in the inset, and the end-systolic (total) and end-diastolic (passive) points are fitted with cubic polynomial functions (dotted lines). (C) Average active stress–length relations of control (solid line) and hypertrophic rat (broken line) trabeculae, calculated by subtracting the passive stress from total stress, n = 12. Data from an exemplar trabecula are shown in the inset and fitted with cubic regression. The SEM for each relation is shown at the maximal stress obtained at Lo. The difference between average regression lines was analyzed by the random coefficient model; *, P < 0.05.