Effect of maximal β -adrenergic stimulation on force response. A comparison between cAMP-mediated maximal β-adrenergic stimulation and basal condition. Voltage clamp protocol used is a 50 ms step pulse to 10 mV from a holding potential of -40 mV. (A) Traces for normalized isometric force developed for increasing stimulation frequencies from 4.0 Hz to 8.0 Hz. The inset shows a plot of the maximum rate of relaxation (R
) versus maximum rate of contraction (R
) for increasing stimulation frequency. (B) The frequency dependence of the maximum and minimum myoplasmic C a2+ concentration. (C) Rate dependence of the maximum and minimum normalized force generated. (D) Frequency dependence of minimum sarcomere length achieved at peak contraction.