The involvement of sodium transport in the volume regulation of the amphipod crustacean, Gammarus duebeni.

Abstract

ABSTRACT The effect on sodium influx of reduction in the fluid volume of the amphipod Gammarus duebeni has been investigated. Removal of water and sodium by exposure to isotonic sucrose or mannitol results in no significant change in blood concentration but is followed subsequently by a marked increase in sodium influx. The increased influx is due, at least in part, to increased active uptake of sodium. Physical removal of blood by pipette stimulates a greater degree of increased uptake in some individuals by comparison with the controls. For technical reasons the increases as measured are smaller than in §2 above and in some individuals there is no response. When the blood concentration is caused to rise at the same time as body volume is reduced there is subsequent decrease in sodium influx. It is concluded that a mechanism is present which initiates an increase in sodium uptake on reduction of blood volume. This mechanism may be of value in replacing fluid loss resulting from haemorrhage, if water uptake accompanies sodium uptake. The evolutionary significance of such a mechanism is discussed in relation to development of active transport mechanisms in present-day freshwater and brackish-water forms.