UPTAKE OF ORGANIC MATERIAL BY AQUATIC INVERTEBRATES. III. UPTAKE OF GLYCINE BY BRACKISH-WATER ANNELIDS

¹ Dept. of Zoology, University of Minnesota, Minneapolis, Minnesota 55455

1. Both Nereis limnicola and Nereis succinea are capable of removing glycine from dilute solution in the surrounding medium at intermediate and high salinities. Uptake declines rapidly at sea water concentrations of chlorosity less than 200 meq./l.

2. The uptake is linear with time for periods of at least one hour, and appears to take place across the body wall without the necessary participation of the gut. Uptake is an exponential function of wet weight.

3. The relation between ambient concentration of glycine and rate of uptake suggests that an adsorptive step becomes limiting in the process of uptake at high concentrations of glycine. A plot of the reciprocal of uptake versus the reciprocal of ambient glycine concentration (Burk-Lineweaver plot) is linear and permits estimation of the apparent V_max and K_m for the process.

4. In N. limnicola, the adaptation of the physiological system mediating glycine uptake to a change in salinity is a process extending for more than 14 days.

5. Conditions which produce an increase in uptake of glycine at low ambient concentrations in N. limnicola also produce a significant increase in estimated maximum velocity and a decrease in the estimated K_m from a Burk-Lineweaver plot. This suggests that the increase reflects a change in the process which cannot be explained as merely an increase in the number of available sites for uptake, since this would not influence the K_m.

6. Both species are capable of removing glycine from solutions of galactose and of sodium chloride whose osmotic concentrations are approximately equal to that of sea water at 200 meq. Cl^-/l, although the rates are significantly below those observed in sea water.

7. The rate of uptake observed in N. succinea exceeds that in N. limnicola by an order of magnitude. This is correlated with the distribution of the latter species, which occurs at lower salinities, and with its greater osmoregulatory ability at low concentrations of the medium.

8. The salinity of the medium at which the process of glycine uptake declines agrees closely with estimates of the point of onset of osmoregulation and of chloride regulation in the two worms. This, together with the widespread ability of marine invertebrates to remove amino acids from solution and the failure to demonstrate this capacity for fresh-water forms, leads to the suggestion that the processes of glycine uptake and osmoregulation are incompatible.