Differences in intestinal electrophysiological parameters and nutrient transport rates between eels (Anguilla anguilla) at yellow and silver stages

Morphological and physiological characteristics of the European eel (Anguilla anguilla) intestine were analyzed in two different stages (yellow and silver) of the fish ontogenic development. Intestine/body (Wi/Wa) and scraped mucosa/intestine (Wsc/Wi) wet weight ratios were significantly (P < 0.01) reduced in seawater acclimated silver eels compared to yellow ones. Electrogenic, Na+-dependent transport rates of a number of nutrients (D-glucose, L-proline, beta-alanine, L-phenylalanine, L-methylalanine) were indirectly measured in intestinal brush border membrane vesicles of seawater acclimated eels, by monitoring the fluorescence quenching of the electrical membrane potential sensitive dye 3,3'-diethylthiocarbocyanine iodide [Dis-C-2(5)], and were significantly lower (P < 0.05 for L-proline; P < 0.01 for all the others) in silver eels compared to yellow ones. The transepithelial electrical potential difference (Vt) and short-circuit current (Isc), measured by applying the short-circuit current technique to ''in vitro'' isolated intestine, were significantly higher in silver eels compared to yellow ones in both sea- and freshwater. The addition of 10(-5) M bumetanide, inhibitor of the Na+-K+-2Cl(-) cotransporter, to the mucosal bathing solution almost completely abolished Vt and Isc in either yellow or silver eel intestine acclimated to both seawater and freshwater. Further, by using the microelectrode technique, it was shown that the apical membrane potential (Vm) averaged -27.3 +/- 2.3 mV in yellow eels and -42.9 +/- 3.3 mV in silver eels (P = 0.02). It is concluded that the changes in morphological (mucosal weight) and physiological (nutrient transport rates and electrophysiological parameters) characteristics found in silver compared to yellow eel intestine could represent adaptative features preparatory to the onset of the prolonged marine migration of the silver eel.