RYR2 and hydrops fetalis: Under voltage-clamp conditions, it shows that (1) hyperphosphorylated RyRs contribute more to the SR Ca2+ release flux than (2) upregulated INCX and decreased SERCA activity, and (3) all combined cases (i.e., hyperphosphorylated RyR, upregulated INCX, and decreased SERCA) for HF (Figure 6A).