Modulation of beta-receptors as adult and neonatal cardiac myocytes progress into culture.

Modulation of beta-adrenergic receptors and their ability to respond to beta-receptor stimulation was studied in cultures of adult and neonatal rat cardiac myocytes. The radioligand iodocyanopindolol (125I-CYP) was used to identify beta-adrenoceptors on the intact cells. 125I-CYP was found to bind to the receptors in a stereospecific and saturable manner. Freshly isolated neonatal and adult myocytes both had a receptor density of approximately 50 fmol/mg protein. The number of beta-receptors per milligram protein was similar during a 10-d culture period for adult myocytes but increased after a 5-d culture period for neonatal myocytes. Both cell types responded to beta-receptor stimulation with isoproterenol by a twofold increase in the concentration of cAMP and this response increased with time in culture. The number of receptors as well as the response to isoproterenol was similar for neonatal myocytes cultured on laminin, collagen type I, or on uncoated culture dishes. From these data we conclude that cultured cardiac myocytes maintain functional beta-receptors as they progress into culture, and the expression of beta-receptors is not influenced by culture substrates.