Modulation of Iron Uptake in Heart by L-Type Ca Channel Modifiers Possible Implications in Iron Overload

Heart failure is the leading cause of mortality in patients with transfusional iron (Fe) overload in which myocardial iron uptake ensues via a transferrin-independent process. We examined the ability of L-type Ca channel modifiers to alter Fe uptake by isolated rat hearts and ventricular myocytes. Perfusion of rat hearts with 100 nmol/L Fe and 5 mmol/L ascorbate resulted in specific Fe uptake of 20.461.9 ng of Fe per gram dry wt. Abolishing myocardial electrical excitability with 20 mmol/L KCl reduced specific Fe uptake by 6067% (P,0.01), which suggested that a component of myocardial Fe uptake depends on membrane voltage. Accordingly, Fe uptake was inhibited by 10 mmol/L nifedipine (45612%, P,0.02) and 100 mmol/L Cd (8663%; P,0.001) while being augmented by 100 nmol/L Bay K 8644 (61618%, P,0.01) or 100 nmol/L isoproterenol (40612%, P,0.05). By contrast, uptake of 100 nmol/L ferric iron (Fe) was significantly lower (1.460.3 ng Fe per gram dry wt; P,0.001) compared with divalent iron. These data suggest that a component of Fe uptake into heart occurs via the L-type Ca channel in myocytes. To investigate this further, the effects of Fe on cardiac myocyte L-type Ca currents were measured. In the absence of Ca, noninactivating nitrendipine-sensitive Fe currents were recorded with 15 mmol/L [Fe]o. Low concentrations of Fe 21 enhanced Ca current amplitude and slowed inactivation rates, which was consistent with Fe entry into the cell, whereas higher Fe levels caused dose-dependent decreases in peak current. Fe had no effect on current amplitude or decay. Combined, our data suggest that myocardial Fe uptake occurs via L-type Ca channels and that blockade of these channels might be useful in the treatment of patients with excessive serum iron levels. (Circ Res. 1999;84:1302-1309.)