Ion transport in the gill epithelium of aquatic crustacea

In recent years a convincing body of knowledge has been accumulated indicating transport mechanisms for osmolytes in marine and brackish water Crustacea. Cuticle and epithelium cell layers serve as selective communications for the exchange of ions and small organic molecules between crustacean gills and their environment. The following apparent permeability coefficients in the Carcinus posterior gill epithelia was measured: PRb : PNa : PCl = 1.7 : 1.0 : 0.1. In addition to the presence of ouabain sensitive unidirectional Na exchange (Ja…︁>b) located on the basolateral gill surface, there is also located an oppositely‐directed, ouabain‐sensitive Rb (K) unidirectional flux. Basolaterally applied ouabain inhibits NH4 fluxes (Jb…︁>a) and seems to interact with the Na/K exchanger, in which NH4 appears to substitute for K. In isolated perfused posterior gills, amiloride affected sodium fluxes and transbranchial potentials, supporting the possible presence of an Na/H exchanger. A unique electrogenic 2Na/H antiporter present in membrane vesicles of marine invertebrates has been discussed with the aim to integrate the knowledge at the different functional levels. Branchial cell acidification was studied in Carcinus hemilamellae microspectrofluorimetrically using the fluorescent dye BCECF. In the case when hemilamellae were immersed in Na‐free solution, intracellular acidification was not affected by amiloride. In addition, in perfused gill epithelia in DSW (200 mM Na) identical with the bathing solution, acetazolamide‐inhibited acidification of the perfused medium was observed. The effects of the inhibitors on the transbranchial potentials (TBP) and their role in the ion transport mechanisms of the crustacean gills are reported.