Holliday, C.W. (1987). Branchial Na, K-ATPase and osmoregulation in the isopod, Idotea woesnesenskii. J. Exp. Biol. 136: 259-272.
Pleopod Na, K-ATPase enzyme specific activity (ESA) and osmoregulatory performance were measured in isopods acclimated for 12-14 days in 100%, 75%, 50% and 25% sea water (SW). The animal was 63-65 mosmol/kg hyperosmotic to the medium in 100% and 75% SW, 214 mosm/kg hyperosmotic in 50% SW and 239 mosm/kg hyperosmotic in 25% SW. The five pairs of pleopods are biramous but are not similar. The two anterior pairs do not stain with silver, have low and unchanging ESA, are smaller and more rigid than the three posterior pairs and are used for swimming. The posterior three pairs are thinner and more flexible; their endopodites stain with silver and have fivefold higher ESA than their exopodites or the front two pleopods. Only the exopodites of the posterior three pleopods showed large (twofold) increases in ESA in animals acclimated in dilute media. The time course of acclimation from 100% to 50% SW was measured: osmotic equilibrium occurred after 1 day; posterior endopodite ESA was elevated after 1 day and was fully activated after 3 days. Ablation of the endopodites of the posterior three pleoppods eliminated the animals' ability to hyperosmoregulate in 50% SW; ablation of the exopodites of the same appendages of of both rami of the first two pairs of pleopods had no significant effect on osmoregulation. Thus, the endopodites of the posterior three pleopods of I. woesnesenskii are the sites of inward ion transport in dilute media.
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