Figure 3

Isosarcometric contraction. Twitch response - Isosarcometric contraction (A) Modulation of sarcomere length - (i) Steady state F-Ca relationships for increasing SL. (ii) Traces for normalized force with SL varied from 1.8 (+) to 2.3 (∗) μ m in increments of 0.1 μ m. The C a^{2 +} transient responsible for each of the traces is shown in the overlay. The inset shows the rate of relaxation versus rate of contraction for increasing sarcomere length (reciprocal of RT₅₀, time taken for 50% sarcomere relaxation versus reciprocal of TTP, time taken for peak sarcomere contraction). (iii) Phase plots of self normalized force versus instantaneous [C a^{2 +} ] _myo for increasing SL overlayed with two steady state F-Ca relationships corresponding to SL = 1.8 (+) and 2.3 μ m (∗). (B) Modulation of Peak [C a^{2 +} ] _myo - (i) Steady state F-SL relationships for increasing background [C a^{2 +} ] _myo . (ii) Sarcomere length is held constant at 2.3 μ m while the peak [C a^{2 +} ] _myo transient is scaled down by decreasing the voltage clamp pulse duration. The traces show the contractile response corresponding to myoplasmic C a^{2 +} transients with peak values 1.1(∗), 0.9, 0.8, 0.7, 0.6, 0.5 (∙) μ M. The inset shows the relationship between TD₅₀ (time taken from 50% activation to 50% relaxation) and activator C a^{2 +} . (iii) Phase plots of self normalized force versus instantaneous [C a^{2 +} ] _myo for increasing peak [C a^{2 +} ] _myo overlayed with a steady state F-Ca relationships corresponding to SL = 2.3 μ m (∗). Model generated data corresponds to an idealized rat ventricular myocyte at 22.5°C.