Na++K+-ATPase in the osmoregulating clam Rangia cuneata.

Of six tissues sampled from the osmoregulating clam Rangia cuneata, mantle contained the highest concentration of Na++K+-ATPase activity and ouabain binding sites. Acclimation to low salinities was accompanied by adaptive increases in Na++K+-ATPase activity in mantle but not in gill. Since the number of ouabain binding sites did not show parallel increases, the mechanism of acclimation to reduced salinity in Rangia appears to involve activation of pre-existing pump sites in the mantle epithelium.