Rubidium Uptake Is Increased in Shore Crabs, Carcinus maenas, Acclimated to Dilute Seawater

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In dilute seawater, Carcinus maenas hyperosmoregulates by actively absorbing Na, K, and Cl. Here we characterize K uptake using a novel technique. Rb was used as a tracer for K transport, and hemolymph Rb levels were measured using cation chromatography. Hemolymph Rb was detectable at 0.1 mmol L−1, which enabled determination of initial rate of Rb uptake. Crabs maintained for 3 wk in dilute artificial seawater (35% ASW crabs) maintained Na and K above the level of the external media and had elevated Na‐K‐ATPase activity in the posterior gills. In assay conditions matched to 100% ASW, Rb uptake was the same in 35% ASW crabs ($0.45\pm 0.04$ μmol g−1 h−1) and in crabs acclimated to normal seawater (100% ASW crabs, $0.49\pm 0.05$ μmol g−1 h−1). In assay conditions matched to 35% ASW, Rb uptake was greater in 35% ASW crabs ($0.28\pm 0.03$ μmol g−1 h−1) compared with 100% ASW crabs ($0.10\pm 0.04$ μmol g−1 h−1). Low external [Rb] or reduced salinity were found to contribute independently to the difference between 100% ASW and 35% ASW crabs. Thus, whole‐body Rb uptake in crabs can be measured by cation chromatography, and Rb uptake is greater in 35% ASW crabs than in 100% ASW crabs.


Physiological and Biochemical Zoology





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