IDENTIFICATION AND MOLECULAR CHARACTERIZATION OF A HIGH-AFFINITY CARDIOMYOCYTE TRANSFORMING GROWTH-FACTOR-BETA-2 RECEPTOR

Rat neonatal heart muscle cells (cardiomyocytes) were found to express a high-affinity surface receptor for transforming growth factor-beta2 (TGF-beta2). 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) less-than-or-equal-to 26 pM TGF-beta2, a B(max) of approximately 9 fMol/10(6) cells, and approximately 5,000 binding sites/cardiomyocyte. Binding was selective for TGF-beta2 in comparison to other TGF-beta isoforms and to unrelated growth factors. Affinity-binding experiments revealed three types of cardiomyocyte TGF-beta2 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 of TGF-beta may reflect receptor-mediated signal transduction at the cardiomyocyte level.