Kinetics of waterborne strontium uptake in the common carp, Cyprinus carpio, at different calcium levels

Abstract

Abstract-The uptake kinetics of strontium in the common carp (Cyprinus carpio) were characterized in vivo, exposing preacclimated fish to a wide range of Sr 2ϩ (0.27 M-10.0 mM) and Ca 2ϩ (10 M-10 mM) concentrations in water; 85 Sr, 45 Ca, and 47 Ca were used as tracers in determining the uptake, and the possibility of adsorption of the tracers to the exterior of the fish were verified. The uptake rates were determined in the whole body, gills, and blood of the fish after an exposure period of 3 h and were analyzed as a function of the free-ion activity of strontium and calcium in water. With the increase of Sr 2ϩ concentration in the exposure water, Sr 2ϩ uptake did not increase linearly but displayed Michaelis-Menten saturation kinetics, and with the increase of Ca 2ϩ concentration, Sr 2ϩ uptake decreased significantly in the whole body, gills, and blood. The competitive inhibition model fitted to the pooled data for whole-body uptake explains about 94% of the variation in Sr 2ϩ uptake and 71% in Ca 2ϩ uptake, indicating a competitive type of interaction during the transport of these metal ions across the biological interfaces. The maximum uptake rate of Sr 2ϩ (J maxSr ) was estimated to be 243.0 mol/kg/h and that of Ca 2ϩ (J maxCa ) 119.4 mol/kg/h. The apparent K m for Sr 2ϩ uptake increased greatly with the increase of Ca 2ϩ concentration in water (186, 789,and 5,515 M for 35, 348,and 3,480 M Ca 2ϩ , respectively). Estimation of the true K m for Sr 2ϩ uptake (K mSr ) and its inhibitor constant for Ca 2ϩ (K iCa ) yielded the values of 96.3 and 28.5 M, respectively. These values are very close to those obtained for Ca 2ϩ uptake (K mCa ϭ 24.9 and K iSr ϭ 100.9 M). This model provides a mechanistic description of the effect of calcium on strontium uptake from water and, vice versa, in carp.

Accumulation of metals relevant for agricultural contamination in gills of European chub (Squalius cephalus)

“…For example, in the gills of chub from the Sutla River, Sr and Ca were positively associated (R 2 = 0.356, p < 0.0001). This finding was opposite to previous reports that Sr and Ca inhibit each other's uptake completely competitively on the level of the whole organism, as well as in the gills of common carp (Cyprinus carpio) (Chowdhury et al 2000; Chowdhury and Blust 2001), due to uptake of both elements through Ca transport systems located in the chloride cells of gills (Flik et al 1995). In the natural aquatic systems, metals are present in different chemical forms, and, often, metal complexation with water-soluble ligands decreases metal uptake by aquatic organisms.…”

Kinetics of strontium uptake in the scleractinian coral Stylophora pistillata

“…Such linear uptake has already been observed for vertebrates (Chowdhury et al 2000), although for a shorter exposure time (7 h). This result is therefore one of the first showing linear uptake over several days for calcifying organisms such as corals.…”

Stable strontium accumulation by earthworms: A paradigm for radiostrontium interactions with its cationic analogue, calcium

“…The CF values integrated in our study across eight sites and four earthworm species encompassed the range reported by Krivolutsky et al [24] but spanned from 0.10 to 1.42, with the highest values being recorded in soils with low strontium concentrations, and vice versa. This suggests the possibility that for soils with high strontium levels, earthworm uptake of the cation approaches saturation in a fashion analogous to that convincingly demonstrated for strontium uptake by a freshwater fish species [43]. In the absence of detailed information regarding strontium (and calcium) extractable fractions in the field soils (see Rigol et al [42] for methods), and mindful that the physiology and molecular biology of calcium transport in earthworms is poorly known, the present worm data must not be overinterpreted.…”

“…First, soil strontium is undoubtedly a major factor, in much the same way that the edaphic concentrations of nonessential metals (e.g., Cd and Pb) explain a large proportion of the variation in earthworm burdens [14,45]. Second, the loss of proportionality between (Sr:Ca) worm and (Sr:Ca) soil at high (Sr:Ca) soil levels conceivably reflects cation competition for, or saturation of, inwardly directed transport pathways [43]; the enhanced and preferential excretion of strontium when the cation ratio exceeds a threshold [32]; or a mutable capacity to endogenously discriminate against strontium and to favor calcium [33]. However, we found no evidence supporting a breakdown in the ability of earthworms to exclude strontium at elevated exposures [33]; rather, in the free-living populations with long strontium-exposure histories, strontium accumulation (as defined by CF and Sr:Ca ratios) in worm tissue was reduced at higher soil strontium concentrations and (Sr:Ca) soil levels.…”