Calcium Signaling Consequences of RyR2-S4938F Mutation Expressed in Human iPSC-Derived Cardiomyocytes.

Type-2 ryanodine receptor (RyR2) is the major Ca release channel of the cardiac sarcoplasmic reticulum (SR) that controls the rhythm and strength of the heartbeat, but its malfunction may generate severe arrhythmia leading to sudden cardiac death or heart failure. S4938F-RyR2 mutation in the carboxyl-terminal was expressed in human induced pluripotent stem cells derived cardiomyocytes (hiPSC-CMs) using CRISPR/Cas9 gene-editing technique. Ca signaling and electrophysiological properties of beating cardiomyocytes carrying the mutation were studied using total internal reflection fluorescence microscopy (TIRF) and patch clamp technique. In mutant cells, L-type Ca currents (I), measured either by depolarizations to zero mV or repolarizations from +100 mV to -50 mV, and their activated Ca transients were significantly smaller, despite their larger caffeine-triggered Ca release signals compared to wild type (WT) cells, suggesting I-induced Ca release (CICR) was compromised. The larger SR Ca content of S4938F-RyR2 cells may underlie the higher frequency of spontaneously occurring Ca sparks and Ca transients and their arrhythmogenic phenotype.