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

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Abstract
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 and 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 .apprx. 2 .times. 105 transferrin receptors per L-6 myocyte and 2 .times. 104 ovotransferrin receptors per cardiac myocyte present, under the conditions used for the equilibrium binding experiments. The L-6 myocytes grew exponentially under the assay conditions, the cardiac-myocyte cultures were in a non-dividing state. The differences in receptor number per cell apparently reflect changes arising from the differing ion demand made by the cells, under these 2 growth conditions. Myocytes apparently acquire Fe from diferric (ovo) transferrin in a process that involves high-affinity, specific binding to membrane receptors.