-K+ATPase Activity in Gills of t h e Euryhaline Crab Chasmagnathus granulata

The occurrence and response of N a + K + A T P a s e specific activity to environmental salinity changes were studied in gill extracts of all of the gills of the euryhaline crab Chasmagnathus granulata from Mar Chiquita coastal lagoon (Buenos Aires Province, Argentina) All of the gills exhibited a salinity depen­ dent N a + K + A T P a s e activity, although the pat tern of response to environmental salinity was different among gills As described in other euryhaline crabs highest N a + K + A T P a s e specific activity was found in posterior gills (6 to 8), which, with exception of gill 6, increased upon acclimation to reduced salinity However, a high increase of activity also occurred in anterior gills (1 to 5) m diluted media Fur­ thermore, both short and long term differential changes of N a + K + A T P a s e activity occurred among the gills after the transfer of crabs to reduced salinity The fact that variations of N a + K + A T P a s e activity in the gills were concomitant with the transition from osmoconformity to lonoregulation suggests that this enzyme is a component of the branchial íonoregulatory mechanisms at the biochemical level in this crab K e y words: Chasmagnathus granulata — Crustacean — Gill — N a + K + A T P a s e — Osmoregulation