INTESTINAL L-METHIONINE TRANSPORT IN THE CULTURED GILTHEAD BREAM (SPARUS-AURATA)

1. The influx and transepithelial movements of L-methionine and its effects on the electrophysiology and Na-Cl-transport in upper and lower intestine of the cultured fish, Sparus aurata, were measured. 2. The K-m and V-max of L-methionine influx into the tissues were higher in lower intestine than in upper intestine. A prominent diffusion-like transport component was also measured in both segments during influx experiments. 3. Net transepithelial fluxes of L-methionine (1 mM) were observed in both upper and lower intestine, this transport being Na+-dependent. 4. The two intestinal segments exhibited an electrical potential difference (PD) and a short circuit current (I-sc) serosa negative or near zero. Tissue conductance (G(t)) was higher in posterior than in lower intestine. 5. Addition of L-methionine to the mucosal side of lower or upper intestine did not induce changes in PD in either part. 6. Isotopic fluxes of Cl- or Na+ measurements under short circuit conditions showed that there were no net Cl- or Na+ transport in either part. 7. L-Methionine additions to the mucosa did not induce changes in unidirectional fluxes of Cl- or Na+ or in the I-sc in either the anterior or posterior intestine.