title: Cation regulation by the terrestrial isopod Armadillidium vulgare (Crustacea: Isopoda: Oniscidea) during dehydration in air.
abstract: Many terrestrial arthropods display tight osmotic and ionic regulation of the hemolymph during dehydration. In this study, we sought to quantify the level of regulation of the major hemolymph cations in the terrestrial isopod Armadillidium vulgare (Isopoda, Oniscidea). Inulin space measurements showed that the hemolymph comprises 52 ± 2.2% of the hydrated water content but contributes 71 ± 9.8% of water losses during desiccation. Hemolymph concentrations of Na+, K+ and Ca²+ were measured in variably dehydrated animals using ion-selective microelectrodes and compared with predicted concentrations assuming no regulation. Na+ and Ca²+ are quite tightly regulated, showing respective concentration increases of 20.8% and 7.1% following a 50% reduction in hemolymph volume, but K+ showed no measurable regulation. The excreted cation fraction during desiccation is negligible. Sites of ion sequestration were examined by injecting ²²Na and ⁴⁵Ca into the hemolymph of hydrated animals and assaying tissue-specific activities following dehydration. Na+ is apparently sequestered non-specifically by an unknown mechanism. Ca²+ accumulates in the dorsal somatic tissues, possibly in the calcium pool of the cuticle. How A. vulgare avoids significant disruptions of E(m) and neuromuscular function in the absence of K+ regulation, and how it sequesters Na+, both pose intriguing challenges for future work.
authors.affiliation: Department of Biology, Pomona College, 75 West 6th Street, Claremont, CA 91711, USA.
authors.forename: Huishan
authors.initials: H
authors.lastname: Koh
authors.forename: Jonathan
authors.initials: J
authors.lastname: Wright
mesh_terms: D000818:Animals; D002118:Calcium / Q000097:blood*; D002132:Calcium Radioisotopes / Q000378:metabolism; D003681:Dehydration / Q000378:metabolism*; D004064:Digestive System / Q000378:metabolism; D006257:Head / Q000502:physiology; D006458:Hemolymph / Q000737:chemistry / Q000378:metabolism; D033321:Isopoda / Q000502:physiology*; D009928:Organ Specificity; D011188:Potassium / Q000097:blood*; D012964:Sodium / Q000097:blood*; D012979:Sodium Radioisotopes / Q000378:metabolism
chemical_list: D002132:Calcium Radioisotopes; D012979:Sodium Radioisotopes; D012964:Sodium; D011188:Potassium; D002118:Calcium