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 Jimax for glycine influx over the range 7--23 degrees C (Q10 = 5). Concomitant with this increase in Jimax was an increase in experimentally determined Kt, from 23 microM to 134 microM. The relationship between changes in Jimax and measured Kt was adequately described by an equation that takes into account the influence of unstirred layers on the kinetics of carrier-mediated transport. Use of this equation indicated that the changes in measured Kt could be explained by the presence of an unstirred layer approximately 400 micrometer thick over the transporting surfaces(s) of the isolated gill, and that the "true" Kt of the transport process is 1 microM. The very low values of Kt for amino acid uptake measured in intact muscles (1--3 microM) 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.