Figure 5
[ C a2+] jSR . Mechanisms underlying the frequency-dependent modulation in SR C a2+ content. Voltage clamp protocol used is a 50 ms step pulse to 10 mV from a holding potential of -40 mV. (A) [ C a2+] jSR traces indicating rate-dependent changes in SR filling. The inset shows the frequency dependence of the maximum and minimum SR C a2+ concentration. (B) Frequency dependence of the maximal pumping rate of SERCA and the average level of phosphorylated PLB. (C) Frequency-dependent increase in average levels of activated auxiliary proteins CaMKII and CaN in the myoplasm. (D) Frequency dependence of the half-activation constant for the forward and backward flow via the SERCA pump. (E) Rate dependence of the relative role of the SERCA pump (when compared to the N a+/ C a2+ exchanger (I NaCa )and the plasma membrane C a2+ ATPase pump (I PMCA ).