Determination of long-life radiocesiums Cs-134 and Cs-137 in food by gamma-ray spectrometry: summary of collaborative study.

A collaborative study was conducted to validate a gamma-ray spectrometric method for determining cesium-134 and cesium-137 in foods. The Cs-134 and Cs-137 contents are measured with a low-resolution, shielded TI-activated Nal scintillation detector connected to a multichannel gamma-ray spectrometer. Thirteen laboratories participated in the study. Participants received 8 samples of heather honey, milk, and mixed dried herbs, including 4 blind duplicates. The accuracy of mean measurements of both isotopes was in the range of 98 to 103%, compared with reference measurements made in one laboratory using a high-resolution GeLi detector. Repeatability relative standard deviation (RSDr) values varied from 4.3 to 11.7% for 2 Cs-134 levels ranging from 121 to 337 Bq/kg and from 2.0 to 7.3% for 4 Cs-137 levels ranging from 210 to 1130 Bq/kg. Reproducibility relative standard deviation (RSDR) values ranged from 10.7 to 14.9% for Cs-134 and from 4.1 to 7.4% for Cs-137. No outliers were identified, and the method worked well in the absence of "fresh" fission products. However, the method was less appropriate for radiocesium determinations for activity concentration < 100 Bq/kg at a counting time of 900 s or when Cs-137/Cs-134 activity ratio was larger than 10. The gamma-ray method for determining Cs-134 and Cs-137 in foods has been adopted first action by AOAC INTERNATIONAL.

Increased transport of inorganic phosphate in renal brush borders of spontaneously hypertensive rats.

Phosphate metabolism was studied in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) by measuring serum phosphate concentrations and 24-h urinary phosphate excretions in rats placed in metabolic cages from 6 to 23 wk of age. Serum phosphate concentrations in SHR were significantly lower than those in WKY at 6, 12, and 20 wk of age. In addition, 24-h urinary phosphate excretion was lower in SHR relative to WKY from 6 through 23 wk of age. The hypophosphaturia in SHR was accompanied with an increase in the maximal transport rate of Na+-dependent phosphate transport in renal brush border membrane vesicles (BBMV) isolated from kidney cortex at 6, 12, and 20 wk of age. The apparent affinity for phosphate did not differ significantly between WKY and SHR at all ages studied. A direct relationship between maximal Na+-dependent phosphate transport rates in BBMV and serum phosphate concentrations was observed in both strains. In SHR, phosphate homeostasis is disturbed from 6 wk of age on.

ATP-dependent Ca2+ transport and Na+/Ca2+ exchange system in renal basolateral plasmamembranes of spontaneously hypertensive rats.

A common abnormality of cellular Ca2+ handling in most tissues of spontaneously hypertensive rats (SHR) has been suggested. Therefore we investigated the ATP-dependent Ca2+ transport and Na+/Ca2+ exchange system in basolateral membrane vesicles (BLMV) of renal cortices from SHR and normotensive Wistar-Kyoto rats (WKY) at 12 and 20 weeks of age. In WKY the maximal transport rate of the ATP-dependent Ca2+ transport was 5.7 nmol/min/mg prot with an affinity for Ca2+ of 0.14 microM. These values were not significantly different in SHR at both ages studied. High concentrations of Na+ inhibited ATP-dependent Ca2+ uptake by 40% in BLMV of SHR and WKY. Low concentrations of Na+ stimulated ATP-dependent Ca2+ transport 20% in both rats. These findings suggest equal Na+/Ca2+ exchange activity in WKY and SHR. The present study failed to show a significant change in ATP-dependent Ca2+ transport and Na+/Ca2+ exchange activity in renal BLMV in SHR, suggesting that the Ca2+ homeostasis of the cortical cells is normal in SHR as far as the plasmamembrane is concerned.

Kinetic properties of the ATP-dependent Ca2+ pump and the Na+/Ca2+ exchange system in basolateral membranes from rat kidney cortex.

Basolateral plasma membranes from rat kidney cortex have been purified 40-fold by a combination of differential centrifugation, centrifugation in a discontinuous sucrose gradient followed by centrifugation in 8% percoll. The ratio of leaky membrane vesicles (L) versus right-side-out (RO) and inside-out (IO) resealed vesicles appeared to be L:RO:IO = 4:3:1. High-affinity Ca2+-ATPase, ATP-dependent Ca2+ transport and Na+/Ca2+ exchange have been studied with special emphasis on the relative transport capacities of the two Ca2+ transport systems. The kinetic parameters of Ca2+-ATPase activity in digitonin-treated membranes are: Km = 0.11 microM Ca2+ and Vmax = 81 +/- 4 nmol Pi/min X mg protein at 37 degrees C. ATP-dependent Ca2+ transport amounts to 4.3 +/- 0.2 and 7.4 +/- 0.3 nmol Ca2+/min X mg protein at 25 and 37 degrees C, respectively, with an affinity for Ca2+ of 0.13 and 0.07 microM at 25 and 37 degrees C. After correction for the percentage of IO-resealed vesicles involved in ATP-dependent Ca2+ transport, a stoichiometry of 0.7 mol Ca2+ transported per mol ATP is found for the Ca2+-ATPase. In the presence of 75 mM Na+ in the incubation medium ATP-dependent Ca2+ uptake is inhibited 22%. When Na+ is present at 5 mM an extra Ca2+ accumulation is observed which amounts to 15% of the ATP-dependent Ca2+ transport rate. This extra Ca2+ accumulation induced by low Na+ is fully inhibited by preincubation of the vesicles with 1 mM ouabain, which indicates that (Na+-K+)-ATPase generates a Na+ gradient favorable for Ca2+ accumulation via the Na+/Ca2+ exchanger. In the absence of ATP, a Na+ gradient-dependent Ca2+ uptake is measured which rate amounts to 5% of the ATP-dependent Ca2+ transport capacity. The Na+ gradient-dependent Ca2+ uptake is abolished by the ionophore monensin but not influenced by the presence of valinomycin. The affinity of the Na+/Ca2+ exchange system for Ca2+ is between 0.1 and 0.2 microM Ca2+, in the presence as well as in the absence of ATP. This affinity is surprisingly close to the affinity measured for the ATP-dependent Ca2+ pump. Based on these observations it is concluded that in isolated basolateral membranes from rat kidney cortex the Ca2+-ATPase system exceeds the capacity of the Na+/Ca2+ exchanger four- to fivefold and it is therefore unlikely that the latter system plays a primary role in the Ca2+ homeostasis of rat kidney cortex cells.