Beta-adrenergic receptor function in cultured AT-1 cardiomyocytes.

AT-1 cells are highly differentiated, contracting cardiomyocytes derived from atrial tumours in transgenic mice. The aim of this study was to characterize beta-adrenergic receptor function and associated intracellular calcium regulation in AT-1 cells. Equilibrium binding experiments with [3H]-CGP-12177 showed a Kd = 0.30 +/- 0.08nM and a Bmax = 2.25 +/- 0.47 fmol/10(5) cells. Competition binding experiments with CGP-20712A showed presence of predominantly beta 1-adrenoreceptors. S-(-)propranolol, atenolol and R-(+)propranolol showed a competitive inhibition of binding with successively lower affinity. Isoproterenol, 2 microM, for 48 hours down-regulated the number (p < 0.05) of beta-adrenergic receptors/cell by about 50%; 10 microM for one hour increased the cAMP concentration (p < 0.05) by about 100%. Cytosolic [Ca2+] was measured flourimetrically in spontaneously and synchronously beating AT-1 cells. The resting cytosolic concentration was 94 +/- 10 nM. The observed sinusoidal Ca2+ oscillation frequency increased after addition of 10 microM isoproterenol (p < 0.02). This effect was antagonized by 10 microM alprenolol (p < 0.01). In conclusion, AT-1 cells have functional beta-adrenoreceptor signalling pathways and constitute an important tool in cardiac biology.