Figure 5.

Effects of PTx pretreatment on the concentration-dependent modulatory actions of MCh on forskolin-stimulated cyclic AMP accumulations in CHO-m3 and -m2m3 cells. (a) CHO-m3 and (b) CHO-m2m3 cell monolayers were pretreated with PTx (100 ng ml⁻¹, 24 h) or vehicle before challenge with the indicated concentrations of MCh for 10 min before addition of forskolin (10 μM). After a further period of 10 min, incubations were terminated and cyclic AMP mass determined as described in the Methods section. Results are expressed relative to the cyclic AMP responses to forskolin alone (CHO-m3: −PTx, 1008±41; +PTx, 433±50; CHO-m2m3: −PTx, 908±110; +PTx, 526±51 pmol mg⁻¹ protein), which are set to 100% for each condition. Data are shown as means±s.e. mean for four (CHO-m3) or five (CHO-m2m3) separate experiments performed in duplicate. PTx did not significantly affect the modulatory effect of MCh in CHO-m3 cells, but significant differences were seen in toxin-treated CHO-m2m3 cells (^*P<0.05).