The effects of acetylcholine, dopamine and 5-hydroxytryptamine on water pumping rate and pressure in the mussel Mytilus edulis L

Acetylcholine (ACh) and dopamine (DA), at certain concentrations, are known inhibitors of ctenidial lateral cilia. Addition of either reduces water pumping rate in intact Mytilus edulis by a maximum of 60–70%. The remaining 30–40% of flow is probably generated by the abfrontal cilia which are unaffected by either substance. Reduced pumping rate results in a reduction of exhalant aperture size which almost maintains exhalant water velocity. Exhalant pressure is slightly reduced after addition of either substance. Addition of 5-hydroxytryptamine (5-HT) causes an initial small reduction in water pumping rate, but rate recovers to pre-addition levels after 10–15 min.