Purification of Endothelin From a Conditioned Medium of Cardiac Fibroblastic Cells Using Beating Rate Assay of Myocytes Cultured in a Serum-free Medium

A conditioned medium from cardiac fibroblastic cells stimulated the beating of quiescent cardiac myocytes cultured in a serum-free medium. The aim of this study was to isolate and characterize the myocyte beat-stimulating activity of the conditioned medium of fibroblastic cells. Cardiac myocytes and fibroblastic cells were isolated individually from neonatal rats. The fibroblastic cells were grown in a growth medium until they became confluent, then serum-free conditioned medium was obtained from them. For the beating-rate assay, the cardiac myocytes were cultured in a completely serum-free medium. The beat-stimulating factor of myocytes in the conditioned medium was purified by reverse-phase liquid chromatographies and gel filtration, and was characterized by measuring the molecular weight of the activity and a pharmacological antagonistic study. The beat-stimulating activity in the conditioned medium was purified into two active fractions. Both of the activities have a molecular weight of 2.5 kDa, and the activities were abolished similarly by FR139317, an endothelin type-A receptor antagonist. These results indicate that cardiac fibroblastic cells secrete endothelin and that this may contribute in part to the functional abnormalities of the heart in patients with myocardial fibrosis.