Fig. 5.

I_Ca,L and Ca²⁺ transient (upper), sarcoplasmic reticulum Ca²⁺ load and intracellular Ca²⁺ buffering (middle) and total cytosolic Ca²⁺ concentrations during I_Ca,L triggering (lower) in control (Ctrl) induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) pre-treated with EMD57033 (5 µM). A Voltage-clamp protocol (upper), representative simultaneous recordings of I_Ca,L (middle) and corresponding I_Ca,L-triggered Ca²⁺ transients (CaT, lower) in untreated Ctrl iPSC-CM (left) and Ctrl iPSC-CM pre-treated with EMD57033 (right). B Peak I_Ca,L amplitude (left) and integrated I_Ca,L (right). C Diastolic and systolic [Ca²⁺]_i (left) and Ca²⁺ transient amplitude (right). D Representative recordings of caffeine-induced Ca²⁺ transient i.e. free cytosolic Ca²⁺ concentration (upper) with associated depolarising inward current (I_NCX, middle) in untreated Ctrl iPSC-CM (left) and Ctrl iPSC-CM pre-treated with EMD57033 (right). Integrated I_NCX as an index for total cytosolic Ca²⁺ concentration was plotted against corresponding cytosolic free Ca²⁺ concentration (lower). Buffer curves depicting the relationship between cytosolic free and total Ca²⁺ were fitted with hyperbolic functions. E, F Sarcoplasmic reticulum Ca²⁺, quantified with caffeine-induced Ca²⁺ transient amplitude (E), or area under the curve (Integral) of the corresponding inward current (I_NCX) (F). G Maximum buffer capacity (B_max, left) and dissociation constant (K_d, right), determined from buffer curves. H Representative total cytosolic Ca²⁺ concentration during I_Ca,L-triggered Ca²⁺ transients in untreated Ctrl iPSC-CM (left) and Ctrl iPSC-CM pre-treated with EMD57033 (right). I Total cytosolic Ca²⁺ amplitude. n = number of iPSC-CM from three batches. Data are mean ± SEM. **P < 0.01 and ***P < 0.001 vs. Ctrl using Student’s t test (B, C left, F, G, I) and the Mann–Whitney U test (C right, E)