Integumental amino acid uptake in a carnivorous predator mollusc (Sepia officinalis, Cephalopoda)

The epithelial cells of the integument of body, arms and tentacles of Sepia officinalis present on their apical membrane a well-organised brush border and show the morphological and histochemical characteristics of a typical absorptive epithelium. The ability of the integument to absorb amino acids was investigated both in the arms incubated in vitro and in a purified prep aration of brush border membrane vesicles (BBMV), Autoradiographic pictures of the integument after incubation of the arms in sea-water with or withou t sodium, showed that proline intake was Na+-dependent, whereas leucine int ake appeared to be a largely cation-independent process. Time course experi ments of labelled leucine, proline and lysine uptakes in BBMV evidenced tha t these amino acids are accumulated within the vesicles in the presence of an inwardly directed sodium gradient. The sodium-driven accumulation proves that cationic and neutral amino acids are taken up by the apical membrane of the epithelium of Sepia integument through a secondary active mechanism. For leucine, a 90% inhibition of the uptake was recorded in the presence o f a large excess of the substrate. In agreement with the autoradiography re sults, an analysis of the cation specificity transport in BBMV showed that leucine uptake had a low cation specificity, whereas lysine and proline upt akes were Na+-dependent, An excess of lysine and proline, which share with alanine two different transport systems in the gill epithelium of marine bi valves, reduced eucine uptake. The possible role of the absorptive ability of the integument in a carnivorous mollusc is discussed. (C) 2000 Harcourt Publishers Ltd.