Effect of temperature on the uptake of waterborne strontium in the common carp, Cyprinus carpio (L.)

The effect of temperature on the uptake kinetics of strontium (Sr) in the c ommon carp (Cyprinus carpio) was studied in vivo, exposing pre-acclimated f ish to a wide range of Sr concentrations in water (Sr-total = 0.2-10 000 mu M; Ca-total = 348 muM) at 10, 20, 25 and 30 degreesC. Sr 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 Sr and Ca in water. The uptake of Sr2+ by the whole body, gills and blood i ncreased with temperature and showed saturation kinetics with the increase of Sr2+ activity. Analyzing the observed uptake rates with a Michaelis - Me nten type model showed that the kinetic parameters (J(max), K-m and K-i) fo r both Sr2+ and its analogue Ca2+ are temperature dependent. Thermodynamic analysis of the temperature effects indicates that the Arrhenius activation energies (E-a) required for Sr2+ uptake (91.9 kJ mol(-1)) and Ca2+ uptake (105.9 kJ mol(-1)) in the whole body of carp were constant over the tempera ture range 10-25 degreesC and showed a break in the Arrhenius plots above t his temperature. The Arrhenius plot for the Sr2+ uptake in blood was simila r to that for the whole body uptake with an E-a of 98.1 kJ mol(-1). However , the E-a for Sr2+ uptake in gills was much smaller and constant (58.1 kJ m ol(-1)) over the temperature range of 10-30 degreesC. For a temperature cha nge from 10 to 25 degreesC, the Q(10) for Sr2+-uptake in whole fish, gills and blood were 3.71, 2.29 and 4.05, respectively. Compared with Ca2+ uptake , Sr2+ uptake appears to require a lower activation energy for transport ac ross the solution body interface in carp. The similar pattern of Arrhenius plots and magnitude of activation energies for Sr2+ uptake both in blood an d whole fish suggest that the uptake into the blood across the basolateral membrane is the rate-limiting energy barrier and hence dictates the overall uptake rate of Sr2+ in whole fish. (C) 2001 Elsevier Science BN. All right s reserved.