Fig. 5. Dose-dependent inhibitory effect of pirenzepine on 1 mmol l^–1 ACh-induced luminescence from arm segment of A. filiformis. Values are means ± S.E.M. of maximal intensities of light emitted, expressed as a percentage of those measured in control arm segments, not treated with cholinergic antagonists. **Significant difference between control and treated arm segments (P<0.01).