Transport of amino acids by marine invertebrates

Marine invertebrates transport amino acids and other organic solutes across their body surfaces. This surface absorption, in some instances, may contribute significantly to the overall nutritional requirements for an organism. Amino acids are accumulated against gradients as high as 106:1 to 107:1 (intracellular:extracellular concentration). The transport mechanism that has been consistently observed to account for this process is Na dependent cotransport. A review of the general characteristics of these transport systems characterized in marine invertebrate epithelia indicates certain common features: Na dependency with coupling coefficients of 2:1 or 3:1 (Na:amino acid translocated), influx coupled to membrane potential, and low intracellular Na activity. Under these conditions Na cotransport can readily account for gradients approaching 107:1. These transport systems may play a role in acquisition of nutrients by marine invertebrates, but it has also been suggested that they may play additional roles in osmoregulation, nutrient conservation, and chemo-reception. © 1993 Wiley-Liss, Inc.