D-Glucose transport in decapod crustacean hepatopancreas

Abstract

Physiological mechanisms of gastrointestinal absorption of organic solutes among crustaceans remain severely underinvestigated, in spite of the considerable relevance of characterizing the routes of nutrient absorption for both nutritional purposes and formulation of balanced diets in aquaculture. Several lines of evidence attribute a primary absorptive role to the digestive gland (hepatopancreas) and a secondary role to the midgut (intestine). Among absorbed organic solutes, the importance of d-glucose in crustacean metabolism is paramount. Its plasma levels are finely tuned by hormones (crustacean hyperglycemic hormone, insulin-like peptides and insulin-like growth factors) and the function of certain organs (i.e. brain and muscle) largely depends on a balanced d-glucose supply. In the last few decades, d-glucose absorptive processes of the gastrointestinal tract of crustaceans have been described and transport mechanisms investigated, but not fully disclosed. We briefly review our present knowledge of d-glucose transport processes in the crustacean hepatopancreas. A discussion of previous results from experiments with hepatopancreatic epithelial brush-border membrane vesicles is presented. In addition, recent advances in our understandings of hepatopancreatic d-glucose transport are shown, as obtained (1) after isolation of purified R-, F-, B- and E-cell suspensions from the whole organ by centrifugal elutriation, and (2) by protein expression in hepatopancreatic mRNA-injected Xenopus laevis oocytes. In a perspective, the applicability of these novel methods to the study of hepatopancreatic absorptive function will certainly improve our knowledge of this structurally complex organ.