| Popis: |
Recent advances in the field of stem cell biology have made it possible to develop spontaneously beating myocytes, with cardiac electrophysiological and molecular phenotypes, from skin fibroblasts. Little is reported, however, on Ca-signaling properties of such cells. Here we quantify the Ca-signaling parameters of human iPSCs-derived cardiomyocytes developed from control and CPVT-afflicted subjects with F2483I point mutation in their RyRs. Single 3-6 days hiPSCs were patch-clamped using pipette solutions containing in mM: 0.1 fluo4, 0.1 Ca2+, 0.2 EGTA, 5 Na+. ICa and global Ca-transients were simultaneously measured. Ca-buffer concentrations were set such as to maintain the spontaneous beating frequencies of intact cells. ICa averaged ∼8 pA/pF in 3 hiPSCs cell-lines (2 controls & one RyR-mutant), but with significant variation among cells (2-20 pA/pF). ICa-induced Ca-transients had rapid release but slow uptake kinetics, producing significant maintained components. The voltage-dependence of ICa-activated Ca-transients was bell-shaped, reflecting the voltage-dependence of ICa in both control and mutant cells. The ratio of ICa-activated to caffeine-triggered Ca-transients (efficiency of release) was ∼0.3. INCX activated by caffeine Ca-transients ranged ∼2 pA/pF compared to ∼1.0pA/pF in adult cardiomyocytes. The gain of CICR was voltage dependent, similar to adult cardiomyocytes. Both adrenergic and Ca-channel agonists enhanced ICa markedly, but failed to alter the gain of CICR significantly. Although there were no qualitative differences in Ca-signaling profiles of control and CPVT mutant myocytes, caffeine-triggered Ca-stores were smaller, CICR gain was larger at −30 but not at 0mV, and Ca-sparks longer in duration in mutant myocytes. We concluded that Ca-signaling parameters of hiPSCs-derived cardiomyocytes were similar to those of adult cardiomyocytes, but the CPVT-RyR mutant myocytes had somewhat altered Ca-signaling characteristics consistent with functionally defective RyRs. (Support by: NIH, RO1-HL16152, RO1-HL107600). |
