Mediation of iron uptake and release in erythroid cells by photodegradation products of nifedipine.

The effects of five Ca2+ channel antagonists on iron uptake by erythroid cells were investigated using rabbit reticulocytes and erythrocytes, and transferrin-bound iron and non-transferrin-bound iron (Fe(II)). All of the antagonists except nifedipine inhibited iron uptake, but only at relatively high concentrations (10-100 microM). Nifedipine markedly stimulated the uptake of Fe(II) but not transferrin-bound iron, but only after it had been photodegraded to its nitrosophenylpyridine derivative. This compound was found to mediate Fe(II) exchange between the cytosol and extracellular medium in both directions with both reticulocytes and erythrocytes, but not by the known iron transport processes. The effect could be reversed by washing the cells with ice-cold NaCl solution. It appeared to be relatively specific for Fe(II) since photodegraded nifedipine had little effect on the uptake of Fe(III) or Mn2+. It is suggested that the nitrosopyridine derivative of nifedipine can act as an Fe(II) ionophore and may be of use as an adjuvant in chelator therapy with desferrioxamine in conditions of iron overload.