Caffeine-triggered Ca2-transient decay (reflecting Ca2extrusion through NCX1), as previously
Caffeine-triggered Ca2-transient decay (reflecting Ca2extrusion through NCX1), as previously described.15, 23 We noted a substantial increase in Serca2a-mediated SR Ca2-uptake in pAF (Figure 5B,C), suggesting that the elevated SR Ca2-load might be at least partly GlyT2 Source attributable to enhanced Serca2a-function. RyR2-function We next assessed SR Ca2-leak with all the tetracaine-method of Shannon et al.18 (Figure 6A), whereby SR Ca2-leak is quantified as the drop in [Ca2]i when RyR2 channels are blocked with tetracaine in cardiomyocytes clamped at -80 mV and perfused with Na-Ca2-free bath answer to stop trans-sarcolemmal ion fluxes. Application of caffeine was made use of to assess SR Ca2-load below precisely the same situations. SR Ca2-leak was elevated in pAF (59.six.5 nmolL, n=63) versus Ctl (31.six.1 nmolL, nN=93; P=0.023). The pAF-relatedNIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptCirculation. Author manuscript; accessible in PMC 2015 February 27.Voigt et al.Pageincrease in SR Ca2-leak could possibly be because of intrinsic RyR2 dysregulation or to increased SR Ca2-load (2051.690.8 nmolL, n=63) versus Ctl (1158.468.3 nmolL, n=93; P=0.019; Figure 6C). As a result, we assessed RyR2-expression and phosphorylation-levels by Western-blotting, and RyR2 single-channel properties in lipid-bilayers. RyR2 proteinexpression was drastically elevated in each tissue-lysates and isolated SR-fractions (Figure 6D), with unaltered Ser2814-RyR2 and slightly lowered Ser2808-RyR2 phosphorylation (in SR fractions only). Moreover, we LTE4 Molecular Weight located a significantly-increased single-channel open-probability of RyR2 from pAF-patients (0.007.003, n=84 vs. 0.032.006, nN=84; P=0.021; Figure 6E). These data suggest that each enhanced numbers of channels and enhanced single-channel open-probability could contribute for the elevated SR Ca2-leak in pAF. Computational Modeling of Atrial Ca2-Handling in Ctl and pAF To further probe the function of altered RyR2 and Serca2a functions and linked SR Ca2load increases in pAF-related Ca2-handling abnormalities, we created a novel computational model of Ca2-handling in human atrial cardiomyocytes (Figure 7A). The model might be used to simulate patch-clamp and pharmacological protocols employed experimentally to assess Ca2-handling properties, and allows visualization of your spatial distribution of [Ca2]i in films or line-scan representations (Figure 7B). Parameters in the Ctl model had been optimized to reproduce a wide selection of human atrial-cardiomyocyte Ca2handling properties, which includes: ICa,L-amplitude; amplitude and decay time-constant of ICa,Ltriggered Ca2-transients; SR Ca2-leak; amplitude of caffeine-induced Ca2-transient; and time-constant of caffeine-induced Ca2-transient decay (Figure 7C; On-line Figures IV-VI). Incorporation of pAF-dependent alterations in Serca2a and RyR2 functions (Online Table IV) reproduced experimentally-observed Ca2-handling properties (On-line Figure VII). The handle model with stochastic RyR2-gating showed isolated SCaEs when clamped at -80 mV following repeated depolarizing voltage-clamp actions to achieve steady-state SR Ca2-loading (Figure 8A). Incorporating either the pAF-related boost in SR Ca2-uptake or RyR2 dysregulation (elevated expression and open-probability) improved the incidence of SCaEs. A combination of each alterations within the pAF model developed synergistic effects on SCaEs, with pronounced increases in their incidence and amplitudes, resulting in bigger transient-inward currents (Figure 8B;.
