Electron-microscopic and radioiron studies of iron uptake in newborn rat myocardial cells in vitro.

In vitro cultured myocardial cells from newborn rats were shown to be a good model system for the study of iron uptake and iron metabolism. Ferric ammonium citrate was readily taken up by cells, and about 50% of it was sequestered in ferritin. The rate of iron uptake and/or accumulation in the cells was proportional to its concentration in the medium at 30, 60, and 90 microM but was reduced at 180 microM. At 360 microM iron both the rate of uptake and the total iron taken up was less than at 90 microM iron. Electron-microscopic examination showed endocytotic vesicles and lysosomes containing iron-filled ferritin molecules, as well as normal morphology. In both control and experimental cultures there was an increase with time in the number of lysosomes; however, in the control cultures there were considerably fewer molecules of ferritin seen per lysosome than in experimentals. The number of ferritin molecules apparent in lysosomes increased with time and with increasing concentrations of iron in the medium.