Na+/K+-ATPase activity and immunocytochemical labeling in podobranchial filament and lamina of the freshwater crayfish Astacus leptodactylus Eschscholtz: evidence for the existence of sodium transport in the filaments

Abstract

In the crayfish Astacus leptodactylus, the podobranch, bearing respiratory and ion-transporting filaments, is attached to the lamina. The Na+/K+-ATPase activity is higher in filaments than in lamina. Using a mouse monoclonal antibody directed against the α subunit of Na+/K+-ATPase, and indirect immunofluorescence microscopy, we can observe that the immunoreactivity of the antibody is different for each kind of structure. The lamina presents an ion-transporting type epithelium, which is thick and presents a developed apical infolding system but no developed basolateral infolding system. The immunoreactivity of the antibody in the lamina is very weak. Respiratory filaments present a thin epithelium with a few small apical folds and scarce mitochondria. The immunoreactivity of the antibody in the respiratory filaments is very weak. In contrast, the ion-transporting filament epithelium is thick, presents a short apical infolding system, a well-developed basal infolding system, and numerous mitochondria. The immunoreactivity of the antibody in the ion-transporting filaments is strong. Ion-transporting filaments, which have a cuticle permeable to cations, seem particularly implicated in Na+regulation, by way of the sodium pump.