A peripheral nervous system cell line RT4-B, established by Imada and Sueoka (Dev. Biol., 66:97-108, 1978), was shown to respond to serotonin [5-hydroxytryptamine (5-HT)l and catecholamines. 5-HT induced a small and transient increase in cytosolic free Ca'+ concentration ([Ca2+],) in the RT4-B cells. The increase was effectively blocked by 5-HT2 receptor antagonists (spiperone, ritanserin and mianserin), but not by a 5-HT3 receptor antagonist (MDL72222), or a a,-adrenergic receptor antagonist (prazosin), indicating that RT4-B cells express 5-HT2 receptors. On the other hand, catecholamines increased cyclic AMP production by RT4-B. The order of potency for stimulating cyclic AMP synthesis was isoproterenol > epinephrine >> norepinephrine >> dopamine, and the stimulation was effectively inhibited by the nonselective P-adrenergic receptor antagonist propranolol, but not by the P,-adrenergic receptor antagonist atenolol, suggesting that RT4-B cells express p,-adrenergic receptors.
The differentiating agent N6,2'-0-dibutyryladenosine 3',5'-monophosphate (dibutyryl-CAMP) enhanced the 5-HT-induced [Ca2+1, increase, but not the catecholamine-induced cyclic AMP production. The increase in the 5-HT response paralleled the increase in the density of 5-HT, receptors. n-Butyric acid (2 mM) and 8-bromoadenosine 3',5'-monophosphate (1 mM) also increased the 5-HT response, and the sum of these increases was nearly equal to that induced by dibutyryl-CAMP.
These results indicate that RT4-B is a novel model cell line for th-5 study of 5-HT, and P,-adrenergic receptors and their second messenger responses and for the analysis of the mechanisms how 5-HT2 receptor gene expression is controlled.