Verapamil downregulates iron uptake and upregulates divalent metal transporter 1 expression in H9C2 cardiomyocytes

Abstract

Belgrade rats have a defect in divalent metal transport 1 (DMT1) with a reduced heart iron, indicating that DMT1 plays a physiological role in non‐transferrin‐bound iron (NTBI) uptake by cardiomyocytes. However, L‐type voltage‐dependent Ca2+ channel (LVDCC) blockers were recently demonstrated to significantly reduce NTBI uptake by cardiomyocytes, implying that LVDCC plays a dominant role in NTBI uptake by cardiomyocytes under iron‐overloaded conditions. These findings led us to hypothesize that the LVDCC blocker‐induced reduction in NTBI uptake might result not only from the inhibition of LVDCC‐mediated NTBI uptake but also from the suppression of DMT1‐mediated NTBI uptake. We therefore investigated the effects of the LVDCC blocker verapamil on NTBI uptake as well as DMT1 expression in H9C2 cells by the measurement of radio‐labeled 55Fe(II), reverse transcription polymerase chain reaction (RT‐PCR) and western blot analysis. We demonstrated that verapamil induced a significant reduction in NTBI uptake by H9C2 cells but also unexpectedly a remarkable increase rather than decrease in the expression of DMT1 mRNA and protein in H9C2 cells. Our findings imply that the verapamil‐induced reduction in NTBI uptake by H9C2 cells is not associated with DMT1 and also indicate that verapamil stimulates rather than inhibits DMT1 expression and DMT1‐mediated iron uptake by heart cells.