Figure 1.

Regulation of secretin receptor responsiveness by PKC. (A) Effect of PKC inhibitor GF109203X on secretin-stimulated cyclic AMP accumulation in NG108-15 cells. Cells were incubated with or without GF109203X (2 μM) for 15 min prior to and then during addition of 100 nM secretin. (B) Concentration dependence of PMA-mediated inhibition of secretin receptor signalling. Cells were exposed to increasing concentrations of PMA for 15 min prior to and then during addition of secretin (100 nM) for 15 min. Data in parts (A) and (B) are mean±s.e.mean (bars) values from three independent experiments, each performed in triplicate. (C) Effect of PMA on cyclic AMP accumulation stimulated by secretin (100 nM), forskolin (10 μM), NECA (10 μM) and iloprost (1 μM). Cells were incubated with 1 μM PMA for 15 min prior to and then during agonist challenge at the stated concentrations for 15 min. The last two bars represent data obtained for cells which have been pretreated with 2 μM GF109203X for 15 min prior to co-addition of PMA and secretin or forskolin. Data are mean±s.e.mean (bars) from 4 – 8 independent experiments with each point performed in quadruplicate. Cyclic AMP accumulation in the presence of PMA was expressed as a per cent of the control agonist responses. ^**P<0.01, ^***P<0.001, versus respective controls, one sample t-test. Control cyclic AMP accumulation values (pmol min⁻¹ mg⁻¹ protein) for basal and agonist-treated conditions were as follows: basal, 5.6±1.1; secretin, 27.7±4.3; forskolin, 157.6±12.8; NECA, 81.0±10.30; iloprost, 124.9±15.5.