Combined chronic CaMKII inhibition and phospholamban ablation decreased the maximum Ca2+ release rate by more than 50% at 10 Hz compared to mice lacking phospholamban only.
Combined chronic CaMKII inhibition and PLN ablation slows calcium release at physiological frequencies in isolated mouse ventricular myocytes, with PLN-mediated regulation of calcium uptake diminishing at higher stimulation frequencies.
In cardiac myocytes, the activity of the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is hypothesized to regulate Ca(2+) release from and Ca(2+) uptake into the sarcoplasmic reticulum via the phosphorylation of the ryanodine receptor 2 and phospholamban (PLN), respectively. We tested the role of CaMKII and PLN on the frequency adaptation of cytosolic Ca(2+) concentration (Ca(2+)(i)) transients in nearly 500 isolated cardiac myocytes from transgenic mice chronically expressing a specific CaMKII inhibitor, interbred into wild-type or PLN null backgrounds under physiologically relevant pacing conditions (frequencies from 0.2 to 10 Hz and at 37 degrees C). When compared with that of mice lacking PLN only, the combined chronic CaMKII inhibition and PLN ablation decreased the maximum Ca(2+) release rate by more than 50% at 10 Hz. Although PLN ablation increased the rate of Ca(2+) uptake at all frequencies, its combination with CaMKII inhibition did not prevent a frequency-dependent reduction of the amplitude and the duration of the Ca(2+)(i) transient. High stimulation frequencies in the physiological range diminished the effects of PLN ablation on the decay time constant and on the maximum decay rate of the Ca(2+)(i) transient, indicating that the PLN-mediated feedback on Ca(2+)(i) removal is limited by high stimulation frequencies. Taken together, our results suggest that in isolated mouse ventricular cardiac myocytes, the combined chronic CaMKII inhibition and PLN ablation slowed Ca(2+) release at physiological frequencies: the frequency-dependent decay of the amplitude and shortening of the Ca(2+)(i) transient occurs independent of chronic CaMKII inhibition and PLN ablation, and the PLN-mediated regulation of Ca(2+) uptake is diminished at higher stimulation frequencies within the physiological range.
Werdich et al. (2008) studied Cardiac myocyte calcium handling (n=500). Combined chronic CaMKII inhibition and PLN ablation vs. Mice lacking PLN only was evaluated on Frequency adaptation of cytosolic Ca(2+) concentration transients (maximum Ca2+ release rate at 10 Hz). Combined chronic CaMKII inhibition and phospholamban ablation decreased the maximum Ca2+ release rate by more than 50% at 10 Hz compared to mice lacking phospholamban only.