Contractile force and sarcomere length. Rate-dependent changes in myoplasmic C a2+ concentration, the corresponding contractile force generated and the resulting sarcomere length. Voltage clamp protocol used is a 50 ms step pulse to 10 mV from a holding potential of -40 mV. (A) Frequency dependence of the maximum and minimum myoplasmic C a2+ concentration (B) Traces for normalized isometric force developed at stimulations rates of 4, 5, 6, and 8 Hz. (C) Rate dependence of the maximum and minimum normalized force generated. (D) Phase loops for normalized isometric force vs [ C a2+]
for increasing frequency of stimulation (4.0 Hz to 8.0 Hz) corresponding to panel B. (E) Traces for sarcomere contraction corresponding to isometric force in panel B. (F) Frequency dependence of minimum sarcomere length achieved at peak contraction. The legend for traces in panel B is shared by panel D and E.