Specific membrane receptors for diferric-transferrin in cultured rat skeletal myocytes and chick-embryo cardiac myocytes

A classical approach was used to determine whether myocyte cultures exhibited diferric-transferrin binding phenomena consistent with the presence of specific, high-affinity membrane receptors. Experiments were performed using a continuous cell line, designated L-6, derived from rat skeletal muscle, as well as primary cultures of chick-embryo cardiac myocytes. Rat transferrin isolated from pooled serum was used in experiments involving L-6 cells, and ovotransferrin isolated from hen's egg white was used with the chick-embryo cardiac myocytes. The data from equilibrium binding experiments, corrected for nonspecific binding, and analyzed by Scatchard analysis indicated that there were approximately 2 x 10(5) transferrin receptors per L-6 myocyte and 2 x 10(4) ovotransferrin receptors per cardiac myocyte present, under the conditions used for the equilibrium binding experiments. Whereas the L-6 myocytes grew exponentially under the assay conditions, the cardiac-myocyte cultures were in a non-dividing state. It is thought that the differences in receptor number per cell reflect changes arising form the differing ion demand made by the cells, under these two growth conditions. It is clear that myocytes acquire iron from diferric (ovo)transferrin in a process that involves high-affinity, specific binding to membrane receptors.