Influence of salinity on the localization and expression of the CFTR chloride channel in the ionocytes of the European sea‐bass Dicentrarchus labrax during ontogeny.

Abstract

The European sea‐bass is a euryhaline teleost whose high osmoregulatory abilities allow sea‐lagoon migrations. Cellular and molecular approaches were combined to determine the osmoregulatory function of CFTR (“Cystic Fibrosis Transmembrane Conductance Regulator”) in different organs during ontogeny. At hatch, immunolocalization shows an apical localization of CFTR in the digestive tract and tegumental ionocytes, suggesting ion excretion. During ontogeny, the secretion site shifts from the tegument to the gills. In the kidney, the CFTR expression is transitory before the larva‐juvenile transition. Juvenile‐like physiological abilities are acquired just before metamorphosis. Sea water (SW) induces dehydration. In the posterior intestine, the basal CFTR may facilitate ionic absorption, perhaps in relation to water uptake through aquaporin. Excess ions are excreted through the gills and rectum, as shown by the apical CFTR. In fresh water (FW), CFTR is apical, suggesting chloride secretion. Expressions of protein and transcript of CFTR were followed after a transfer from SW to FW. In gills and intestine, after the transfer, the transcript expression and the protein quantity decrease, to lower the chloride eflux. These changes in CFTR expression according to salinity constitute one of the adaptive mechanisms for sea‐lagoon migrations.