Identification and molecular characterization of a high‐affinity cardiomyocyte transforming growth factor‐β2 receptor

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Abstract
Rat neonatal heart muscle cells (cardiomyocytes) were found to express a high‐affinity surface receptor for transforming growth factor‐β2 (TGF‐β2). Specific binding was rapid, saturable, ligand‐selective, and reversible. Equilibrium binding analyses revealed that the cardiomyocyte had one class of specific binding sites with a K d ⩽ 26 pM TGF‐β2, a B max of ~9 fmol/106 cells, and ~5,000 binding sites/cardiomyocyte. Binding was selective for TGF‐β2 in comparison to other TGF‐β isoforms and to unrelated growth factors. Affinity‐binding experiments revealed three types of cardiomyocyte TGF‐β2 binding proteins, the most prominent of which corresponded to the high‐molecular mass proteoglycan. These data raise the possibility that the anti‐ischemic cardioprotective effects ofTGF‐β may reflect receptor‐mediated signal transduction at the cardiomyocyte level.