Fig. 1.

PKC activation by PMA downregulates [³H]CCK-8 accumulation in human SCH. (A) Time-dependent accumulation of [³H]CCK-8 (1 μM) in human SCH. Data represent the mean ± range of duplicate measurements from a single donor. (B) Effect of PKC activator PMA on [³H]CCK-8 accumulation. [³H]CCK-8 accumulation (1 μM for 3 minutes) was determined in human SCH pretreated with PMA (black bars) or a PMA inactive analog, 4αPDD (gray bars), for 30 minutes at 0.1 or 1 μM. (C) Involvement of PKC activation in PMA-induced downregulation of [³H]CCK-8 accumulation. Human SCH were incubated in medium containing 0.1 or 1 μM PMA for 30 minutes in the presence (white bars) or absence (black bars) of pretreatment (20 minutes) and subsequent coincubation (30 minutes) with the PKC inhibitor BIM I (1 μM). [³H]CCK-8 accumulation (1 μM, 3 minutes) in human SCH was expressed as a percentage of the accumulation measured in vehicle-treated cells. Data represent mean ± S.E.M. from n = 3 donors in triplicate. *P < 0.05 versus control by one-way analysis of variance, followed by Dunnett’s t test. Transport experiments were performed on day 5 or 6 of culture.