Modulation of enzymatic activities by molting cycle in hepatopancreatic R cells of Marsupenaeus japonicus

Four cell types compose the crustacean hepatopancreas: E (embryonic), R (resorptive), F (fibrillar) and B (blister-like) cells. The physiological activity played by these cells seems to be affected by different physiological/environmental conditions such as the molting cycle, nutritional state, osmoregulation, etc. The aim of the present study was to evaluate whether the activities of different enzymes, i.e. acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), plasma membrane calcium ATPase (PMCA), sarco-endoplasmic calcium ATPase (SERCA) were expressed in the R cells and then affected by the molting cycle. ACC and FAS are involved in the de novo fatty acid synthesis being ACC generally considered the rate limiting step of this metabolic pathway. The characteristics of ACC and FAS have been extensively studied in both mammalian and fish liver. In this respect, however, no information is so far available in marine invertebrates. The calcium pump activities were investigated since the epithelial cells of the crustacean hepatopancreas play an important role in Ca2+ balance. ACC and FAS activities were assayed at different temperatures in fresh cells coming from hepatopancreas of shrimps at the pre-moult stage. The highest activities of both ACC and FAS were found at 25 °C. When these enzymatic activities were measured as dependence of moult stage, intermoult was the stage in which both ACC and FAS activities showed their maximum value. SERCA and PMCA activities were detected only in early premoult stage. The results obtained demonstrated that the molting cycle affects important metabolic pathways and are in agreement with the role carried out by the R cells mainly represented by lipid and calcium storage.