Serotonin-induced inward current in rat facial motoneurons: evidence for mediation by G proteins but not protein kinase C

The 5-HT-induced inward current in rat facial motoneurons was rendered irreversible by intracellular GTP gamma S, an hydrolysis-resistant analog of guanosine 5'-triphosphate which sustains G protein activation. Conversely, the 5-HT response was reduced by GDP beta S, an analog of guanosine 5'-diphosphate which interferes with G protein activation. Inhibitors of protein kinase C enhanced the 5-HT-induced inward current. Thus, the slow inward current induced by 5-HT in facial motoneurons appears to be mediated by G proteins but modulated negatively by protein kinase C.