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22Docosahexaenoic acid (DHA) is an essential fatty acid necessary for many biochemical, 23 cellular and physiological functions in fish. However, high dietary levels of DHA 24 increase free radical injury in sea bass larvae muscle, even when vitamin E (α-25 tocopherol, α-TOH) is increased. Therefore, the inclusion of other nutrients with 26 complementary antioxidant functions, such as vitamin C (ascorbic acid, AA), could 27 further contribute to prevent these lesions. The objective of the present study was to 28 determine the effect of AA inclusion (3600 mg/kg) in high DHA (5% DW) and α-TOH 29

Complementary RNA, derived from the intestine of the sea bass Dicentrarchus labrax and putatively coding for a pH-dependent oligopeptide transporter PepT1 (SLC15 family), was injected in Xenopus oocytes that were subsequently tested with electrophysiological techniques. Transport-associated currents were observed when various di- or tripeptides were applied at concentrations ranging between 0.1 and 10 mM. No currents were generated by histidine nor by other single amino acids. Sea bass PepT1 also exhibited presteady-state currents in the absence of substrates. Acidic pH slowed down the relaxation time constant of these currents and shifted both Q/V and tau/V relationships toward more positive voltages. Michaelis-Menten analysis of the transport currents showed an increase in apparent substrate affinity at acidic pH, which was very similar to that exhibited by the related transporter from zebrafish (Danio rerio), but in contrast, did not demonstrate a significant effect of pH on the maximal transport current.

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