Effect of maximal β -adrenergic stimulation on C a2+ dynamics. 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) Rate dependence of peak IC a,L current. (B) Frequency dependence of the maximum pre-release SR C a2+ concentration. (C) [ C a2+]
traces showing rate-dependent effects on systolic C a2+ concentration in the myoplasm for increasing stimulation frequencies from 4.0 Hz to 8.0 Hz.