Abstract 11087: T-type Calcium Channel is a Main Portal for Iron Entry in Thalassemic Heart
Iron-overload cardiomyopathy is responsible for many deaths in thalassemia patients. Although L-type calcium channel (LTCC) was proposed as a portal for iron entry and deposit in the heart, its role in the heart of thalassemia subject has never been investigated. Growing evidence demonstrated that reexpression of T-type calcium channel (TTCC) was found in diseased myocardium of adult hearts. However, its existence and role for iron entry in thalassemic hearts is unknown. We tested the hypothesis that both LTCC and TTCC are the main portals for iron entry in thalassemic hearts.
Methods: Hearts from heterozygous β-globin knockout thalassemic (HT) mice and wild-type (WT) mice (n=8/group) were used for cultured ventricular cardiomyocytes. Various iron (Fe2+) concentrations (10–160 mg/ml) and pharmacological interventions with transferin receptor (TfR) blocker and divalent metal transporter inhibitor (ebselen), LTCC blocker (verapamil), TTCC blocker (efonidipine), and iron chelator desferoxamine (DFO) were used to investigate the mechanisms of iron uptake in cardiomyocytes, using Calcein-AM fluorescence assay. Levels of LTCC and TTCC gene expression in heart tissues was done by microarray analysis.
Results: Iron uptake under iron-overload conditions in the thalassemic cardiomyocytes was greater than that of wild type cells (p<0.01). TTCC blocker, efonidipine, could prevent iron uptake into cardiomyocytes in a dose-dependent manner (low fluorescence intensity=high iron uptake into cells and vice versa, Fig-A) similar to that of DFO. TfR blocker, ebselen and verapamil could not prevent iron uptake into cells (Fig-B). Microarray analysis showed highly up-regulated genes of TTCC but no change in LTCC genes in thalassemic hearts.
Conclusions: Our findings indicated that iron uptake mechanisms in thalassemic cardiomyocytes are mainly mediated by TTCC, suggesting that unlike normal heart, TTCC is the important pathway for iron entry in thalassemic hearts.
- © 2010 by American Heart Association, Inc.