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 (A nguilla anguilla) intestine were analyzed in two different stages (yel low and silver) of the fish ontogenic development. Intestine/body (Wi/ Wa) and scraped mucosa/intestine (Wsc/Wi) wet weight ratios were signi ficantly (P < 0.01) reduced in seawater acclimated silver eels compare d to yellow ones. Electrogenic, Na+-dependent transport rates of a num ber 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 fluor escence quenching of the electrical membrane potential sensitive dye 3 ,3'-diethylthiocarbocyanine iodide [Dis-C-2(5)], and were significantl y lower (P < 0.05 for L-proline; P < 0.01 for all the others) in silve r eels compared to yellow ones. The transepithelial electrical potenti al difference (Vt) and short-circuit current (Isc), measured by applyi ng the short-circuit current technique to ''in vitro'' isolated intest ine, were significantly higher in silver eels compared to yellow ones in both sea- and freshwater. The addition of 10(-5) M bumetanide, inhi bitor of the Na+-K+-2Cl(-) cotransporter, to the mucosal bathing solut ion 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 membr ane 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 transpo rt rates and electrophysiological parameters) characteristics found in silver compared to yellow eel intestine could represent adaptative fe atures preparatory to the onset of the prolonged marine migration of t he silver eel. (C) 1996 Wiley-Liss, Inc.