. Frequency-dependent characteristics of the DHP-sensitive C a2+ channel IC a,L, which forms the trigger current. Voltage clamp protocol used is a 50 ms step pulse to 10 mV from a holding potential of -40 mV. (A) IC a,L at different frequencies of stimulation ranging from 0.5 Hz to 8.0 Hz. Inset gives an expanded view of the rate-dependent modulation of IC a,L over the range of frequencies investigated (B) Dependence of peak IC a,L current on frequency of stimulation (C) Frequency-dependent increase in average levels of activated auxiliary proteins CaMKII and CaN in the dyad (D) Frequency-dependent modulation of peak open probability of the DHP-sensitive C a2+ channel. (E) Rate-dependent changes in IC a,L upstroke velocity.