Acute reversal of phospholamban inhibition facilitates the rhythmic whole-cell propagating calcium waves in isolated ventricular myocytes

Here, we used the Fab fragment of 2D12, a monoclonal anti-PLB antibody, to test how acute reversal of PLB inhibition affects the spontaneous SR Ca2 + release in normal VMs. Ca2 + sparks and spontaneous Ca2 + waves (SCWs) were recorded in the line-scan mode of confocal microscopy using the Ca2 + fluorescent dye Fluo-4 in isolated permeabilized mouse VMs. Fab, which reverses PLB inhibition, significantly increased the frequency, amplitude, and spatial/temporal spread of Ca2 + sparks in VMs exposed to 50 nM free [Ca2 +]. At physiological diastolic free [Ca2 +] (100-200 nM), Fab facilitated the formation of whole-cell propagating SCWs. At higher free [Ca2 +], Fab increased the frequency and velocity, but decreased the decay time of the SCWs. cAMP had little additional effect on the frequency or morphology of Ca2 + sparks or SCWs after Fab addition. These findings were complemented by computer simulations. In conclusion, acute reversal of PLB inhibition alone significantly increased the spontaneous SR Ca2 + release, leading to the facilitation and organization of whole-cell propagating SCWs in normal VMs. PLB thus plays a key role in subcellular Ca2 + dynamics and rhythmic activity of VMs.