Osmoregulatory plasticity of the glass eel of Anguilla anguilla: freshwater entry and changes in branchial ion-transport protein expression

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Abstract:

The glass-eel stage of the life history of Anguillid eels (Anguilla spp.) makes the important physiological transition from seawater (SW) to freshwater (FW) osmoregulation. Central to successful adaptation to fresh water is the switch from active hypoosmoregulation (ion excretion) to active hyperosmoregulation (ion uptake) to counter passive fluxes imposed by concentration gradients. Anguilla anguilla (L.) glass eels, captured from the lower Minho River estuary and maintained in brackish water (BW; 24‰), were fully capable of adapting to FW following acute transfer. In a comparison between SW- (34‰) and FW-adapted glass eels, gill Na+/K+-ATPase and Na+:K+:2Cl cotransporter (NKCC) expression were both markedly reduced in the FW group. Branchial mitochondria-rich chloride cells (MRCs) were also significantly larger in SW-adapted glass eels. Apical CFTR Cl channel immunoreactivity associated with branchial MRCs was also only present in SW-adapted glass eels. The expression of these three ion-transport proteins is strongly associated with active ion excretion in SW teleost fishes. In FW-adapted glass eels, cortisol treatment increased branchial Na+/K+-ATPase expression but was without effect on NKCC expression. Glucocorticoid receptor blockade by RU-486 had no effect on Na+/K+-ATPase or NKCC expression.

Le stade civelle du cycle biologiques des anguillidés (Anguilla spp.) assure la transition physiologique importante de l'osmorégulation en eau salée à celle en eau douce. Le passage d'une hypo-osmorégulation (excrétion d'ions) active à une hyper-osmorégulation (absorption d'ions) active pour contrebalancer les flux passifs générés par les gradients de concentration est essentiel au succès de l'adaptation aux eaux douces. Des civelles d'Anguilla anguilla (L.) récoltées dans l'estuaire inférieur du Minho et gardées en eau saumâtre (BW, 24 ‰) sont parfaitement capables de s'adapter à l'eau douce (FW) à la suite d'un transfert rapide. Une comparaison des civelles adaptées à l'eau de mer (SW, 34 ‰) et à l'eau douce montre une réduction marquée de l'expression de la Na+/K+-ATPase et du cotransporteur Na+:K+:2Cl (NKCC) des branchies chez le groupe d'eau douce. Les cellules à chlorures riches en mitochondries (MRC) des branchies sont aussi significativement plus grandes chez les civelles en eau de mer. L'immunoréactivité apicale du canal Cl-CFTR associée aux MRC des branchies ne se manifeste que chez les civelles en eau de mer. L'expression de ces trois protéines (transport d'ions) est fortement associée à l'excrétion active d'ions chez les téléostéens d'eau salée. Chez les civelles d'eau douce, un traitement au cortisol augmente l'expression de la Na+/K+-ATPase des branchies, mais elle reste sans effet sur celle de NKCC. Le blocage des récepteurs glucocorticoïdes par RU-486 n'a aucun effet sur l'expression de la Na+/K+-ATPase, ni sur celle de NKCC.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2004

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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