Figure 8.

Sensitivity of individual experiments to the combined effects of receptor antagonists to 5-HT3 and 5-HT4 receptors. (A) Shows control data of the proportion of individual colonic preparations that showed repeated temporary blockade of repetitive peristaltic contractions with increasing concentrations of SDZ-205–557 and ondansetron. The table shows responses of 6 control animals to consecutive application of increasing concentrations of ondansetron and ondansetron (1–10 μM) and responses to 4 preparations treated with reserpine and also with mucosa and submucosal plexus removed. Interestingly, in reserpinized preparations, with mucosa and submucosal plexus removed, peristaltic contractions rarely recovered in the presence of both antagonists and most 3 of 4 animals were blocked at 1 μM, whereas in control animals, 4 out of 6 animals required 10 μM to permanently block these contractions. In (A), it can be seen that 1 out 6 preparations was abolished at 1 μM of these antagonists, then increasing the concentration to 5 μM one additional preparation was blocked, then the remaining 4 preparations were all blocked at 10 μM. (B) In contrast, in reserpine-treated mucosa-free preparations, no preparations were blocked at 1 μM, but all were abolished at 3 μM.