Effect of strontium and magnesium on blood calcium]

Twenty four male Wistar rats weighing 250 +/- 10 g, in three groups of 8 rats each, were used. Group A was used as control and the content of its drinking water was 6.5 mg/l Ca; 2.4 mg/l Mg. The drinking water of groups B and C was supplemented with 20 mM (SrCl2) and 20 mM (MgCl2), respectively. Once the 20 days of mineral supplementation had passed, arterial blood was extracted by puncture in the abdominal aorta. In the serum obtained after centrifugation, Ca, Mg, Sr and the total proteins (TP) were determined. Afterwards the serum was subjected to ultrafiltration. Concentrations of Ca, Mg and TP were measured in the obtained ultrafiltrates (u), with the above described techniques. The pH was measured before and after the ultrafiltration. The TP decreased significantly both in group B (supplemented with Sr), and in group C (supplement with Mg). Increases in Ca were found in group B and in Mg in group C. The Mg/Ca ratio increased 10% after the supplementation with Mg. At the ultrafiltrate a significant increase in Cau after supplementation with Sr and with Mg was observed. The Mgu/Cau ratio decreased 14% in the group supplemented with Sr and 38% after the supplementation with Mg. In conclusion, the supplementation with Sr (20 mM) in rats increases the Cau and could have the effect of reducing protein synthesis. These facts should be borne in mind when Sr is used for therapeutical purposes.     

Thromboxane and prostacyclin generation by human umbilical veins after thrombin.

Prostacyclin (PGI2) and Thromboxane B2 (TxB2) production induced by thrombin in human umbilical veins (HUV) was studied. Successive stimulations of HUV segments were performed with and without restoration of arachidonic acid (AA). Thrombin consistently stimulated the production of both substances. The magnitude of the increment declined with progressive stimuli. The addition of exogenous AA could restore the production of TXB2 but not that of PGI2. These results suggest that sustained stimulation of AA release may lead to an imbalance in the TXA2/PGI2 ratio perhaps through an effect of unknown products of AA oxidation on PGI2 synthase.     

Modelling of the disulphide-swapped isomer of human insulin-like growth factor-1: implications for receptor binding.

Insulin-like growth factor-1 (IGF-1) is a serum protein which unexpectedly folds to yield two stable tertiary structures with different disulphide connectivities; native IGF-1 [18-61,6-48,47-52] and IGF-1 swap [18-61,6-47, 48-52]. Here we demonstrate in detail the biological properties of recombinant human native IGF-1 and IGF-1 swap secreted from Saccharomyces cerevisiae. IGF-1 swap had a approximately 30 fold loss in affinity for the IGF-1 receptor overexpressed on BHK cells compared with native IGF-1.The parallel increase in dose required to induce negative cooperativity together with the parallel loss in mitogenicity in NIH 3T3 cells implies that disruption of the IGF-1 receptor binding interaction rather than restriction of a post-binding conformational change is responsible for the reduction in biological activity of IGF-1 swap. Interestingly, the affinity of IGF-1 swap for the insulin receptor was approximately 200 fold lower than that of native IGF-1 indicating that the binding surface complementary to the insulin receptor (or the ability to attain it) is disturbed to a greater extent than that to the IGF-1 receptor. A 1.0 ns high-temperature molecular dynamics study of the local energy landscape of IGF-1 swap resulted in uncoiling of the first A-region alpha-helix and a rearrangement in the relative orientation of the A- and B-regions. The model of IGF-1 swap is structurally homologous to the NMR structure of insulin swap and CD spectra consistent with the model are presented. However, in the model of IGF-1 swap the C-region has filled the space where the first A-region alpha-helix has uncoiled and this may be hindering interaction of Val44 with the second insulin receptor binding pocket.     

Effect of defrosting on quantity of volatile amines in stored sardines and herring used for tuna fattening

Studied were the quantities of volatile amines, total volatile bases nitrogen (TVB‐N) and trimethylamine nitrogen (TMA‐N) in stored sardines (Sardina pilchardus) and herring (Clupea harengus) over a 24‐h period after defrosting. At the beginning of the experiment analyses showed TVB‐N quantities in the flesh of both species to be higher than the FAO‐recommended limit. TMA‐N concentrations exceeded the acceptance limit 6 h after defrosting in herring samples and after 12 h in sardines. During the entire experiment TMA‐N and TVB‐N concentrations in sardines were above the tolerance limit. The defrosting method usually applied in tuna farms is unsuitable for maintenance of a high quality food supply. Low quality baitfish can cause reduced weight gain as well as induce health problems and mortality in farmed tuna (Thunnus thynnus) populations.     

The influence of alkyl pyridinium sponge toxins on membrane properties, cytotoxicity, transfection and protein expression in mammalian cells

The ability of two alkyl pyridinium sponge toxin preparations (poly-APS and halitoxin) to form transient pores/lesions in cell membranes and allow transfection of plasmid cDNA have been investigated using HEK 293 cells. Poly-APS and halitoxin preparations caused a collapse in membrane potential, reductions in input resistance and increased Ca²⁺ permeability. At least partial recovery was observed after poly-APS application but recovery was more rarely seen with halitoxin. The transfection with plasmid cDNAs for an enhanced green fluorescent protein (EGFP) and human tumour necrosis factor receptor 2 (TNFR2) was assessed for both toxin preparations and compared with lipofectamine. Stable transfection was achieved with poly-APS although it was less efficient than lipofectamine. These results show that viable cells transfected with alien cDNA can be obtained using novel transient pore-forming alkyl pyridinium sponge toxins and a simple pre-incubation protocol. This provides the first proof of principle that pore-forming alkyl pyridinium compounds can be used to deliver cDNA to the intracellular environment without permanently compromising the plasma membrane.     

Isolation of Actinomycetes synthesizing proteases with thrombolytic activity

Proteases with the thrombolytic activity were studied in 212 strains of actinomycetes isolated from different soils of the Soviet Union. The cultures belonged to the genera Micromonospora, Nocardia and Streptomyces. Proteases were synthesized by 41% of the studied actinomycetes and some of their strains completely dissolved in vitro artificially obtained blood thrombi within 120-240 min. In the Streptomyces genus, more active strains were found in the groups Flavus, Fradia and Globisporus. The groups Olivaceus, Violaceus and Viridis had less active strains.