Is the Coelomic Plasma of Phascolosoma arcuatum (Sipuncula) Hyperosmotic and Hypoionic in Chloride to the External Environment?

概要

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Since Phascolosoma arcuatum lives in the mud of the mangrove swamp, which is subjected to extremely variable salinities, the present studies were undertaken to examine if this sipunculid could, to a certain extent, regulate ions and/or volume. When acclimated to 30% or 100% seawater (SW), P. arcuatum maintained its coelomic plasma (CP) slightly, but significantly, hyperosmotic to the external medium. Maintenance of a slightly hyperosmotic coelomic fluid would favor a constant, yet small, osmotic water influx which would compensate for urine production and any other process by which water is lost. The Cl-concentration in the CP of this sipunculid was always lower than that of the external medium. The difference in the Cl- concentration between the CP and the external medium in specimens acclimated to 100% SW was greater than that in specimens acclimated to 30% SW. Specimens acclimated to 100% SW also contained significantly greater concentrations of inorganic phosphate, organic phosphates and water-soluble proteins in the CP than those acclimated to 30% SW. The hypoionic Cl- condition in the CP of this worm might be essential for the accommodation of negatively charged organic osmolytes in the CP without violating electroneutrality. Hence, it was concluded that P. arcuatum could regulate to a certain extent its ionic compositions in the CP and maintain the CP hyperosmotic to the external medium.
社団法人日本動物学会の論文
1994-12-15