Abstract
The effect of 5โhydroxytryptamine (5โHT) on influx of ^14^Cโglycine in isolated gills of Mytilus was studied. 5โHT 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 ^14^Cโinulin from gills treated with 5โHT. Application of 5โHT at a concentration of 10^โ5^ M increased influx of 1 ฮผM ^14^Cโglycine in isolated gills of M. californianus from control values of less than 0.1 ฮผmoles/(gโhr) to 0.5 ฮผmoles/(gโhr). Influx of 1ฮผM glycine in gills from M. edulis treated with 5โHT was more than 700% of control values. 5โHT had no effect on uptake of glycine in intact, actively pumping M. californianus, indicating that 5โHT'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 ฮผM to 20 ฮผM by treatment of gills from M. californianus with 5โHT. 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.