Down-regulation of protein kinase C blocks 5-HT-induced enhancement in Hermissenda B photoreceptors.

Light paired with serotonin (5-HT) in vivo produces both short and long-term enhancement of generator potentials in identified B-photoreceptors in Hermissenda. The contribution of protein kinase C to the induction of enhancement was assessed by pretreatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA), which produces a depletion or down-regulation of protein kinase C. Presentation of light and 5-HT after an 8 h pretreatment with TPA blocked the induction of enhancement of light-evoked generator potentials. Typical enhancement produced by light and 5-HT was observed after pretreatment with an inactive phorbol (4 alpha-phorbol). These results indicate that activation of protein kinase C is an important step in the induction of enhancement.