Effect of activity of lateral cilia on transport of amino acids in gills of Mytilus californianus

The effect of 5‐hydroxytryptamine (5‐HT) on influx of ¹⁴C‐glycine in isolated gills of Mytilus was studied. 5‐HT was observed to induce metachronal activity of lateral cilia in in vitro preparations of gills of M. californianus and M. edulis. Active lateral cilia were capable of increasing perfusion of isolated gills of M. californianus, as demonstrated by a significant reduction in the t_1/2 for washout of ¹⁴C‐inulin from gills treated with 5‐HT. Application of 5‐HT at a concentration of 10⁻⁵ M increased influx of 1 μM ¹⁴C‐glycine in isolated gills of M. californianus from control values of less than 0.1 μmoles/(g‐hr) to 0.5 μmoles/(g‐hr). Influx of 1μM glycine in gills from M. edulis treated with 5‐HT was more than 700% of control values. 5‐HT had no effect on uptake of glycine in intact, actively pumping M. californianus, indicating that 5‐HT's effect on transport in isolated gills is a result of activating lateral cilia rather than a direct effect on the transport process. The Michaelis constant for influx of glycine was reduced from a control value of 44 μM to 20 μM by treatment of gills from M. californianus with 5‐HT. These observations are consistent with the hypothesis that in vitro preparations of mussel gill have unstirred layers that introduce a significant bias into determinations of transport kinetics. Extrapolation of results obtained with isolated gills to intact animals is dubious.