Triadin Deletion Alters Calcium Sparks in Murine Cardiomyocytes

Gene-targeted deletion of the sarcoplasmic reticulum (SR) protein triadin (Trdn-/-) causes 50% reduction in ryanodine receptor (RyR2) Ca2+ release channels and cardiac calsequestrin, and a 50% decrease in the size of t-tubule SR junctions in mouse heart muscle. Here we report on the Ca2+ spark properties of Trdn-/- cardiomyocytes. Isolated ventricular myocytes from Trdn-/- mice (N=5) and wild-type littermates (Trdn+/+, N=8) were loaded with the Ca-sensitive fluorescent indicator Fluo4-AM and Ca2+ sparks were measured in 2mM Ca2+ by confocal microscopy in line scan mode. As illustrated in the figure, triadin deletion caused a dramatic reduction in spark amplitude (ΔF/Fo: Trdn-/- 0.43±0.01, n=893; Trdn+/+ 0.61±0.02, n=745, p<7.27E-22), spark width (FWHM (μm): Trdn-/- 2.64±0.03 n=893, Trdn+/+ 2.90 ± 0.03, n=745, p<1.77E-09) and spark upstroke velocity (Δ(F/Fo)/Δtmax(Δ(F/Fo)/s): Trdn-/- 31.67±0.90, n=891, Trdn+/+ 58.35±1.62, n=741, p<3.49E-48), whereas spark frequency was modestly increased (sparks/100μm/s: Trdn-/- 0.92±0.08, n=255 myocytes, Trdn+/+ 0.71±0.06, n=321 myocytes, p<0.03). The changes in spark properties occurred in absence of significant changes in SR Ca2+ content measured by rapid caffeine application. These data suggest that loss of triadin has a drastic effect on spark properties, possibly by altering the number of RyR2 and/or the RyR2 cluster size.View Large Image | View Hi-Res Image | Download PowerPoint Slide