Kinetics of Waterborne Strontium Uptake in the Common Carp, Cyprinus Carpio, at Different Calcium Levels

The uptake kinetics of strontium in the common carp (Cyprinus carpio) were characterized in vivo, exposing preacclimated fish to a wide range of Sr21 (0.27 mM–10.0 mM) and Ca21 (10 mM–10 mM) concentrations in water; 85Sr, 45Ca, and 47Ca 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 Sr21 concentration in the exposure water, Sr21 uptake did not increase linearly but displayed Michaelis–Menten saturation kinetics, and with the increase of Ca21 concentration, Sr21 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 Sr21 uptake and 71% in Ca21 uptake, indicating a competitive type of interaction during the transport of these metal ions across the biological interfaces. The maximum uptake rate of Sr21 (JmaxSr) was estimated to be 243.0 mmol/kg/h and that of Ca21 (JmaxCa) 119.4 mmol/kg/h. The apparent Km for Sr21 uptake increased greatly with the increase of Ca21 concentration in water (186, 789, and 5,515 mM for 35, 348, and 3,480 mM Ca21, respectively). Estimation of the true Km for Sr21 uptake (KmSr) and its inhibitor constant for Ca21 (KiCa) yielded the values of 96.3 and 28.5 mM, respectively. These values are very close to those obtained for Ca21 uptake (KmCa 5 24.9 and KiSr 5 100.9 mM). This model provides a mechanistic description of the effect of calcium on strontium uptake from water and, vice versa, in carp. Keywords—Strontium Calcium Waterborne Uptake kinetics Carp