Immunolocalization of Na+,K+-ATPase in the branchial cavity during the early development of the crayfish Astacus leptodactylus (Crustacea, Decapoda).

The ontogeny of osmoregulation was examined in the branchial cavity of embryonic and early post-embryonic stages of the crayfish Astacus leptodactylus maintained in freshwater, at the sub-cellular level through the detection of the sodium-potassium adenosine triphosphatase (Na(+),K(+)-ATPase). The embryonic rate of development was calculated according to the eye index (EI) which was 430-450 microm at hatching. The distribution of the enzyme was identified by immunofluorescence microscopy using a monoclonal antibody IgGalpha5 raised against the avian alpha-subunit of the Na(+),K(+)-ATPase. Immunoreactivity staining, indicating the presence of Na(+), K(+)-ATPase appeared in the gills of late embryos (EI>/=400 microm), i.e. a few days before hatching time, and steadily increased throughout the late embryonic and early post-embryonic development. The appearance of the enzyme correlates with the ability to osmoregulate which also occurs late in the embryonic development at EI 410-420 microm and with tissue differentiation within the gill filaments. These observations indicate that the physiological shift from osmoconforming embryos to hyper-regulating late embryos and post-hatching stages in freshwater must originate partly from the differentiation in the gill epithelia of ionocytes which are the site of ion pumping, as suggested by the location of Na(+),K(+)-ATPase. Only the gills were immunostained and a lack of specific staining was noted in the lamina and the branchiostegites. Therefore, osmoregulation through Na(+)active uptake is likely achieved in embryos at the gill level; all the newly formed gills in embryos function in ion regulation; other parts of the branchial chamber such as the branchiostegites and lamina do not appear to be involved in osmoregulation.