We examined the ontogeny of the osmoregulatory sites of the branchial cavity in embryonic and early postembryonic stages of the European lobster Homarus gammarus through transmission electron microscopy, immunofluorescence microscopy, and immunogold electron microscopy using a monoclonal antibody IgGα5 raised against the avian α-subunit of the Na+,K+-ATPase. In mid-late embryos, Na+,K+-ATPase was located along the pleurites and within the epipodite buds. In late embryos just before hatching, the enzyme was confined to the epipodite epithelia. After hatching, slight differentiations of ionocytes occured in the epipodites of larval stages. Na+,K+-ATPase was also located in the ionocytes of the epipodites of larvae exposed to seawater (35.0‰) and to dilute seawater (22.1 ‰). After metamorphosis, the inner-side branchiostegite epithelium appeared as an additional site of enzyme location in postlarvae held in dilute seawater. Within the ionocytes, Na+,K+-ATP-ase was mostly located along the basolateral infoldings. These observations are discussed in relation to the physiological shift from osmoconforming larvae to slightly hyper-regulating (in dilute seawater) postmetamorphic stages. The acquisition of the ability to hyper-osmo-regulate probably originates from the differentiation, on the epipodites and mainly along the branchiostegites, of ionocytes that are the site of ion pumping as evidenced by the location of Na+,K+-ATPase. (J Histochem Cytochem 49:1013–1023, 2001)
Proteasomal activities in the claw muscle tissue of European lobster, Homarus gammarus, during larval development
