Energetic costs and efficiencies of ciliary filter feeding

Abstract

The relationship between activity of the lateral cilia and oxygen consumption was studied in fragments of the gills of Mytilus edulis L., and the effects of stimulation with the nerve transmitters serotonin and dopamine were measured. Beat frequency, f, and oxygen consumption, M_{O 2}, increased with increasing doses of the transmitters. Serotonin increased f up to 26 Hz and the relationship with M_{O 2} could be described by M_{O 2} (μl cm^-2 gill area h^-1)=0.44+0.35 f (r=0.99). The relationship after dopamine stimulation did not differ from that established by serotonin, but the maximum value of f was only 19 Hz. At the frequency of 10 Hz, characteristic of undisturbed pumping, the cells carrying the lateral cilia were estimated to account for one third of the total oxygen consumed, equivalent to 1.05×10^-10 mol ATP cm^-2 s^-1. This rate of synthesis of ATP was compared with the rate at which the active cilia hydrolyse ATP. ATP hydrolysis ranged from 58 to 87% of synthesis as the assumed ratio between number of ATP molecules hydrolysed per beat and number of dynein molecules ranged from 2 to 3. The rate at which ATP is hydrolysed by the active cilia was compared with the work done in pumping water. At two estimates available of the pumping pressure, 1.4 and 2.5 mm H₂O, the work amounted to 1.4×10^-6 or 2.5×10^-6 joule cm^-2 s^-1, equivalent to 2.9×10^-11 and 5.2×10^-11 mol ATP cm^-2 s^-1. The efficiencies of work thus corresponded to 48 or 86% at the ATP/dynein ratio of 2. The overall efficiencies of the mussel pump amounted to 18 or 32%.