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/106cells, 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.
