We have used NCB-20, a cloned cell line of mouse neuroblastoma and fetal Chinese hamster brain cell, as a model system to study receptor interactions in the same cell. NCB-20 cells express serotonin (5-HT) receptors coupled to adenylate cyclase. We found that 5-HT and 5-methoxytryptamine activated adenylate cyclase in intact cells with low efficiency (EC 50 values approximately 500 nM), while some putative 5-HT1A receptor agonists, 8-hydroxy-2-(di-n-propylamino) tetralin or 8-OH-DPAT, ipsapirone and buspirone were ineffective. Receptor binding studies also showed that 5-HT was bound of 8-OH-DPAT was detected. These data suggest that 5-HT receptor coupled to adenylate cyclase in NCB-20 cells in distinct from 5-HT1A and may represent a novel class of receptors for 5-HT. We also found that NCB-20 cells are equipped with presynatic components of 5- HT neurons. These include a 5-HT uptake system and specific binding sites for imipramine which inhibits the uptake of 5-HT in a competitive manner. Addition of imipramine activated phosphosphoinositide hydrolysis catalyzed by phospholipase C. This activation was dose-and time-dependent and was nonadditive to that produced by carbachol. Moreover preexposure to imipramine induced a rapid desensitization to the response of imipramine and carbachol. Since NCB-20 cells possess multiple receptors coupled to different effector systems, this cell line is an usual system to study receptor cross-talks at the molecular levels.
