ATP2A3 and hydrops fetalis: Expression of Ca2+- and Na+-handling molecules: in HF, LPFs had reduced levels of mRNA for sarco/endoplasmic reticulum Ca2+- ATPase (SERCA2a) and ryanodine receptor (RyR2) (both on t testing) and RYR3, whereas in RPFs only RyR3 was downregulated (t testing; Figure 5A through 5C).