Basolateral localization of Na+ + K+‐ATPase in gill epithelium of two osmoregulating crabs, Callinectes sapidus and Carcinus maenas

Although Na+ + K+‐dependent ATPase, the enzymatic equivalent of the sodium pump, is thought to be restricted to the basolateral membrane of nearly all ion‐transporting epithelial cells, its absence from basolateral membranes of crustacean epithelia and/or its presence in apical membranes have been suggested by evidence from other laboratories. However, ultracytochemical localization of K+‐dependent, ouabain‐sensitive p‐nitrophenylphosphatase (p‐NPPase), using the method of Mayahara et al. ('80), indicated that Na+ + K+‐ATPase resides predominantly in the basolateral membrane of thick epithelial cells from gill lamellae of two euryhaline crabs, Callinectes sapidus and Carcinus maenas. Crab gill is therefore not unique in its Na+ + K+‐ATPase distribution and may be used as a model for experiments designed to investigate mechanisms of transepithelial Na+ uptake.