Fig. 5. Determination of adenylyl cyclase activity in membrane preparations of IMCD cells. Crude membrane fractions of IMCD cells were prepared, and adenylyl cyclase activity was determined (30 µg protein/reaction). Membranes were left untreated, incubated with AVP (100 nM; 15 minutes), sulprostone (1 µM; 30 minutes) or sulprostone (1 µM; 30 minutes) with AVP (100 nM) added for the final 15 minutes. Data represent the mean ± s.e. of three independent experiments and are calculated as the percentage of AVP-stimulated activity. Absolute values for adenylyl cyclase activity (pmol/mg protein/minute) in the three independent experiments were: basal 15.1, 11.3 and 6.82; AVP: 76.7, 35.7 and 32.8; sulprostone: 21.0, 7.7 and 7.9; sulprostone and AVP: 66.5, 28.8 and 25.3. *, values significantly different from AVP-stimulated control (P<0.05).