The influx of Ca2+ induced by the administration of glucagon and Ca2+-mobilizing agents to the perfused rat liver could involve at least two separate pathways.

The Ca2+-mobilizing actions of ADP, ATP and epidermal growth factor (EGF) and their interaction with glucagon were studied in a perfused liver system incorporating a Ca2+-selective electrode. ADP (1-100 microM), ATP (1-100 microM) and EGF (10-50 nM) all induced a net efflux, followed by a net uptake of Ca2+ in the intact liver. The co-administration of glucagon (or of cyclic AMP) with these agents resulted in a synergistic potentiation of the Ca2+ uptake response in a way which resembles the synergism observed when glucagon is administered with phenylephrine, vasopressin or angiotensin [Altin & Bygrave (1986) Biochem J. 238, 653-661]. The inability of diltiazem, verapamil and nifedipine to inhibit the Ca2+-influx response suggests that the stimulation of Ca2+ influx does not occur through voltage-sensitive Ca2+ channels. By contrast, the synergistic effects of glucagon in the stimulation of Ca2+ influx are inhibited by 10 mM-neomycin, and a lowering of the extracellular pH to 6.8. Simultaneous measurements of perfusate Ca2+ and pH changes suggest that the Ca2+ influx response is not mediated by a Ca2+/H+ exchange. The inability of neomycin and low extracellular pH to inhibit the refilling of the hormone-sensitive pool of Ca2+, after the administration of Ca2+-mobilizing agents alone, provides evidence for the existence in liver of at least two Ca2+-influx pathways, or mechanisms for regulating Ca2+ influx.     

Phosphate and calcium uptake by mitochondria and by perfused rat liver induced by the synergistic action of glucagon and vasopressin.

Co-administration of glucagon and vasopressin to rat liver perfused with buffer containing 1.3 mM-Ca2+ induces a 4-fold increase in Pi in the subsequently isolated mitochondria (from approx. 9 to approx. 40 nmol/mg of mitochondrial protein). This increase is not attributable to PPi hydrolysis, and is not observed if the perfusate Ca2+ is lowered from 1.3 mM to 50 microM. The increase in mitochondrial Pi closely parallels that of mitochondrial Ca2+; when the increase in Pi and Ca2+ accumulation is maximal, the molar ratio is close to that in Ca3(PO4)2. Measurement of changes in the perfusate Pi revealed that, whereas administration of glucagon or vasopressin alone brought about a rapid decline in perfusate Pi, the largest decrease (reflecting net retention of Pi by the liver) was observed when the hormone was co-administered in the presence of 1.3 mM-Ca2+. The synergistic action of glucagon plus vasopressin was nullified by lowering the perfusate Ca2+ to 50 microM. The data provide evidence that, whereas glucagon may be able to alter Pi fluxes directly in intact liver, any alterations induced by vasopressin are indirect and result only from its action of mobilizing Ca2+.     

Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.      

Nucleotide variation at the hypervariable esterase 6 isozyme locus of Drosophila simulans

Esterase 6 (Est-6/EST6) is polymorphic in both Drosophila melanogaster and D. simulans for two common allozyme forms, as well as for several other less common variants. Parallel latitudinal clines in the frequencies of the common EST6-F and EST6-S allozymes in these species have previously been interpreted in terms of a shared amino acid polymorphism that distinguishes the two variants and is subject to selection. Here we compare the sequences of four D. simulans Est-6 isolates and show that overall estimates of nucleotide heterozygosity in both coding and 5' flanking regions are more than threefold higher than those obtained previously for this gene in D. melanogaster. Nevertheless, the ratio of replacement to exon silent-site polymorphism in D. simulans is less than the ratio of replacement to silent divergence between D. simulans and D. melanogaster, which could be the result of increased efficiency of selection against replacement polymorphisms in D. simulans or to divergent selection between the two species. We also find that the amino acid polymorphisms separating EST6- F and EST6-S in D. simulans are not the same as those that separate these allozymes in D. melanogaster, implying that the shared clines do not reflect shared molecular targets for selection. All comparisons within and between the two species reveal a remarkable paucity of variation in a stretch of nearly 400 bp immediately 5' of the gene, indicative of strong selective constraint to retain essential aspects of Est-6 promoter function.      

Carbachol stimulates a different phospholipid metabolism than nerve growth factor and basic fibroblast growth factor in PC12 cells.

We have examined 1,2-diglycerides (DGs) generated in PC12 cells in response to the muscarinic agonist carbachol and compared them with those generated in response to the differentiation factors nerve growth factor and basic fibroblast growth factor. Whereas carbachol stimulates a greater release of inositol phosphates, all three agonists generate similar levels of DGs. In this report, we have analyzed the molecular species of PC12 DGs generated in response to these three agonists. Additionally, we have analyzed the molecular species of PC12 phospholipids. The data indicate that 1) after 1 min of either nerve growth factor or basic fibroblast growth factor stimulation, DGs arise primarily from phosphoinositide hydrolysis; 2) in contrast, after 1 min of carbachol stimulation, DG are generated equally by both phosphoinositide and phosphatidylcholine hydrolysis; and 3) after 15 min of stimulation by any of these agonists, DGs are generated largely by phosphatidylcholine hydrolysis, with a smaller component arising from the phosphoinositides. These results suggest that at least part of the mechanism by which PC12 cells distinguish between different agonists is via alterations in phospholipid sources and kinetics of DG generation.     

Molecular basis of ion permeability in a voltage‐gated sodium channel

Voltage‐gated sodium channels are essential for electrical signalling across cell membranes. They exhibit strong selectivities for sodium ions over other cations, enabling the finely tuned cascade of events associated with action potentials. This paper describes the ion permeability characteristics and the crystal structure of a prokaryotic sodium channel, showing for the first time the detailed locations of sodium ions in the selectivity filter of a sodium channel. Electrostatic calculations based on the structure are consistent with the relative cation permeability ratios (Na⁺ ≈ Li⁺ ≫ K⁺, Ca²⁺, Mg²⁺) measured for these channels. In an E178D selectivity filter mutant constructed to have altered ion selectivities, the sodium ion binding site nearest the extracellular side is missing. Unlike potassium ions in potassium channels, the sodium ions in these channels appear to be hydrated and are associated with side chains of the selectivity filter residues, rather than polypeptide backbones.     

Validation of a rapid micellar electrokinetic capillary chromatographic method for the simultaneous determination of isoniazid and pyridoxine hydrochloride in pharmaceutical formulation

An efficient and reliable micellar electrokinetic capillary chromatography (MEKC) method has been developed for the simultaneous determination of isoniazid (ISO) and pyridoxine hydrochloride (PYR) in pharmaceutical formulations. A chemometric two level full factorial design approach was used to search for the optimum conditions of separation. Three parameters were selected for this study: the buffer pH, the buffer concentration and sodium dodecyl sulphate (SDS) concentrations. Resolution, peak symmetry and analysis time were established as response. The two analytes were separated within 6 min with the optimized conditions: 50 mM borate buffer, 25 mM SDS pH 7.8, 35 degrees C, at 50 mbar 4s injection and 30 kV by using a fused silica capillary (72 cm effective length, 50 microm i.d.). The detection wavelength was set to 205 nm. Meloxicam was used as internal standard. The method was validated with respect to stability, linearity range, limit of quantitation and detection, precision, accuracy, specificity and robustness. The detection limits of the method were 1.0 microg mL(-1) for ISO and 0.40 microg mL(-1) for PYR and the method was linear at least in the range of 3.0-100 microg mL(-1) for ISO and 1.0-100 microg mL(-1) for PYR with excellent correlation coefficients (0.9995 for ISO and 0.9998 for PYR). Relative standard deviations (R.S.D.s) of the described method ranged between 0.54 and 2.27% for intra-day precision and between 0.65 and 2.69% for inter-day precision. The developed method was applied to the tablet form of ISO and PYR-containing the pharmaceutical preparations and the data were compared with obtained from the standard addition method. No statistically significant difference was found.     

Synthesis of the chelator lipid nitrilotriacetic acid ditetradecylamine (NTA-DTDA) and its use with the IAsys biosensor to study receptor-ligand interactions on model membranes

This work describes the synthesis and use of the chelator lipid, nitrilotriacetic acid ditetradecylamine (NTA-DTDA). This lipid is readily dispersed in aqueous media, both alone and when mixed with carrier lipids like dimyristoylphosphatidylcholine (DMPC). Fluorescence microscopic examination of membranes deposited from NTA-DTDA-containing liposomes shows that NTA-DTDA mixes uniformly with the carrier lipid, and does not phase separate. NTA-DTDA-membranes deposited onto the sensing surface of IAsys biosensor cuvettes show good stability, permitting use of the biosensor to study protein interactions. Hexahistidine-tagged proteins including recombinant forms of the extracellular regions of murine B7.1 (B7.1-6H) and of the human erythropoietin receptor (EPOR-6H) bind to NTA-DTDA-membranes; the stability of binding is dependent on both protein concentration, and density of NTA-DTDA. Kinetic measurements show that high stability of anchored proteins (t(1/2) approximately 10-20 h, apparent K(d) approximately 1 nM) can be achieved using membranes containing 25 mol% NTA-DTDA, but low levels of bound protein (<200 arc seconds). The system is used to study the interaction of human EPO with the EPOR anchored onto NTA-DTDA-membranes. In addition to the biological applications reported recently, the results show that NTA-DTDA can be a useful reagent in the study of receptor-ligand interactions.     

The presence of promatrix metalloproteinase-3 and its relation with different categories of coal workers' pneumoconiosis

Extracellular matrix formation (ECM) and remodeling are critical events related to the pathogenesis of pulmonary fibrosis. Matrix metalloproteinases play an essential role in degrading and remodeling the ECM. In this study, we tried to show the presence and correlation of promatrix metalloproteinase-3 (proMMP-3) (the inactive form of metalloproteinase-3) levels in coal workers' pneumoconiosis (CWP) with different categories. The study population consisted of 44 coal miners with CWP (pos CWP). Coal miners without CWP (neg CWP, n = 24) and non-underground personnel (controls, n = 17) were taken as controls. All coal miners were stable and had no systemic infection or disease. Standard posterio-anterior chest radiographs and pulmonary function tests were performed to exclude any diseases other than CWP. Serum proMMP-3 was analysed using the sandwich enzyme-linked immunosorbent assay according to the manufacturer's instructions (The Binding Site, Birmingham, UK). Mean proMMP-3 values of the all three groups were compared and a significant statistical difference obtained (p < 0.001). In addition, a statistically significant difference was found between categories of the disease and proMMP-3 values (p < 0.05). The effects of age, exposure duration and cigarette smoking on proMMP-3 values in coal miners with CWP were investigated. There were no correlations between age, smoking and proMMP-3 values. However, a positive correlation was found between exposure duration and proMMP-3 values (r = 0.447, p = 0.008). In conclusion, proMMP-3 (prostromelysin 1) may play an essential role in degrading and remodeling the ECM in workers with pneumoconiosis. ProMMP-3 may also reflect the stage of pneumoconiosis disease.