The application relates to a cell line ("HL-1") derived from a transplantable mouse cardiomyocyte lineage (AT-1) wherein the cell line has the following characteristics: a) can be serially passaged greater than two hundred times and retain the ability to spontaneously contract; b) can be frozen, stored in, and recovered from liquid nitrogen, and revived upon thawing; c) can be cultured in serum-free medium; d) retains ultrastructural characteristics of in vitro adult atrial cardiac muscle cells; e) displays a pattern of gene expression similar to that of adult atrial myocytes including ANF, atrial natriuretic factor, a-cardiac myosin heavy chain, a-cardiac actin and connexin43; f) responds positively to immunohistochemical stains for desmin, sarcomeric myosin, and atrial natriuretic peptide; g) will give rise to tumors when injected subcutaneously into syngeneic mice h) can secrete into the culture medium growth factors including basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF), epithelial growth factor (EGF), transforming growth factor beta 1(TGF-b1), and adrenomedullin; i) displays a cardiac-like, rapidly activating and inactivating delayed rectifier potassium current with biophysical and pharmacological characteristics that are nearly identical to those described for cardiac Ikr, j) displays time- and voltage-dependent inward currents that are most likely sodium and L-type calcium currents. The application further relates to a cell culture system which can be used as an in vitro model of the cardiac muscle cell to screen and test cardiac drugs.
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