Uptake of Amino Acids by Three Species of Nereis (Annelida: Polychaeta). I. Transport Kinetics and Net Uptake from Natural Concentrations

Abstract

Epidermal uptake of alanine, serine and glutamic acid was investigated in salinities of 18 and 32% in the polychaetes N. succinea, N. virens and N. diversicolor. The 3 amino acids were chosen because they were the most abundant free, interstitial amino acids in sediment from the sampling locality. Glutamic acid was absorbed at low, but similar rates in the 3 spp. in both salinities. In 18.permill., serine was absorbed at equal rates by N. succinea and N. virens, but a lower uptake occurred in N. diversicolor. In 32.permill., serine uptake increased in all species; the greatest increase was found in N. succinea, Alanine was absorbed at almost similar rates in both salinites. The highest uptake occurred in N. succinea, followed by N. virens and N. diversicolor. Uptake kinetics generally demonstrated higher affinities (low Km) and lower potential uptake rates (Vmax) in 18 than in 32.permill.. The uptake capacity in the 3 Nereis spp. did not appear to be related to natural interstitial concentrations of amino acids. The most abundant free, intracellular amino acids were taurine, alanine and glycine. In 32.permill., the proportion of taurine was reduced, compared with 18.permill.. The free amino acid spectrum in the worms was not reflected in capacity or affinity of amino acid uptake. When the Nereis spp. were exposed to natural concentrations of interstitial amino acids, a significant net uptake occurred. Simultaneously a small quantity of amino acids was released. The magnitude of the uptake from natural concentration levels of amino acids suggests that these nereids obtain a considerable energetic benefit under in-situ conditions.