Iron transport through calcium channels in the heart. FPN, ferroportin; FTN, ferritin; LCI, labile cytosolic iron; LPI, labile plasma iron; LTCC, l-type calcium channel; Mfrn, mitoferrin; ROS, reactive oxygen species; RyR₂, ryanodine receptor; SR, sarcoplasmic reticulum; TF, transferrin; TfR1, transferrin receptor-1; TTCC, t-type calcium channel.