Influence of temperature and unstirred layers on the kinetics of glycine transport in isolated gills of Mytilus californianus

The effect of temperature on the kinetics of glycine influx in isolated gills of Mytilus californianus was studied. Increases in temperature resulted in significant increases in the J imar for glycine influx over the range 7–23° C (Q₁₀ = 5). Concomitant with this increase in J imar was an increase in experimentally determined K_t, from 23 μM to 134 μM. The relationship between changes in J imar and measured K_t was adequately described by an equation that takes into account the influence of unstirred layers on the kinetics of carriermediated transport. Use of this equation indicated that the changes in measured K_t could be explained by the presence of an unstirred layer approximately 400 μm thick over the transporting surfaces(s) of the isolated gill, and that the “true” K_t of the transport process is 1 μM. The very low values K_t for amino acid uptake measured in intact mussels (1–3 μM) are revealed to be the product of transport processes of high affinity for substrate and a perfusion system which effectively minimizes the influence of unstirred layers, thereby permitting efficient utilization of substrate at the low concentrations characteristic of these animals' environment.