D‐1 Dopaminergic and β‐Adrenergic Stimulation of Adenylate Cyclase in a Clone Derived from the Human Astrocytoma Cell Line G‐CCM

: Clones have been isolated from the human astrocytoma cell line G‐CCM. Homogenates of clone D384 contain an adenylate cyclase that is stimulated by 3,4‐dihydroxyphenylethylamine (dopamine), noradrenaline, and isoprenaline with Ka apparent values of 4, 56, and 2.7 μM, respectively. The Ka apparent value for dopamine was increased by the D‐l antagonist cis‐flupenthixol, 25 and 100 nM, to 23 and 190 μM, respectively, but was unaffected by propranolol (1 μf. Noradrenaline stimulation of adenylate cyclase was only partially inhibited by either propranolol (10 μM) or cis‐flupenthixol (1 μM). Propranolol (10 μM), but not cis‐flupenthixol (1 μM), prevented stimulation by isoprenaline. The stimulation of adenylate cyclase by dopamine and noradrenaline remained unchanged in the presence of phentolamine (1 μM) and sulpiride (1 μM). These results suggest that clone D384 contains both D‐l dopaminergic and β‐adrenergic receptors coupled to adenylate cyclase. Dopamine stimulates D384 adenylate cyclase through D‐1 receptors, isoprenaline via β‐receptors, and noradrenaline through both receptors.