RYR2 and rheumatoid arthritis: However, several genes critically involved in cardiomyocyte-specific calcium handling, such as cardiac muscle calcium-transporting ATPase (ATP2A2), cardiac ryanodine receptor 2 (RYR2) and phospholamban (PLN), were significantly down-regulated in RA-iPSC-CMs compared with the other groups (Fig. 3d).