Abstract

In euryhalineteleosts, the biochemical mechanisms for maintenance of constant level of ions in body fluids of fish depend mainly on the activity of gill Na⁺, K± ATPase (NKA). The NKA is a P-type ubiquitous membrane-spanning ATPase that actively transports Na⁺ and K⁺ out of and into animal cells. The enzyme activities of gill NKA are affected by environmental ion concentrations. The high activity of NKA is mainly located in the tubular system of the MR cells which plays a central role in the process of ion transport in gills of freshwater and seawater-acclimated fishes. The NKA consist of three subunits; α, β and γ.