SLC8A1 and familial dilated cardiomyopathy: In addition, the activity of the sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 (SERCA2), the ryanodine receptor (RyR) and Na+/Ca2+ exchanger (NCX1) are markedly reduced in DCM, leading to diminished release of Ca2+ from endoplasmic reticulum stores and slowed replenishment of these stores during relaxation.