Nonylphenol alters the activity of splenic NK cells and the numbers of leukocyte subpopulations in Sprague–Dawley rats: a two-generation feeding study

Nonylphenol (NP) has been identified at low levels in surface waters throughout North America. This industrial chemical is primarily used for the production of certain non-ionic surfactants, and has been reported to have weak estrogen-like activity. As estrogen has immunoregulatory properties and is crucial for normal fetal development, it was hypothesized that adult and developmental exposures to NP had the potential to adversely affect the immune system. Furthermore, developmental exposure to NP might also produce differential immunomodulation in F(1) male and female rats. Thus, a two-generation feeding study was conducted to evaluate the potential for NP to modulate certain immune parameters. Pregnant female Sprague-Dawley rats were exposed to NP (0, 25, 500, and 2000 ppm) in their feed for 65 days, beginning 7 days into gestation. The F(1) generation male and female offspring were exposed in utero at the respective treatment levels, commencing the 7th day of gestation, and continuing through to 64 days of age. Changes in splenic antibody-forming cell response, natural killer cell activity, and leukocyte numbers were used to evaluate NP immunotoxicity. The results from the present study indicate that dietary exposure to NP can increase splenic natural killer (NK) cell activity and splenocyte subpopulation numbers in the F(1) generation rats, without similar changes to the F(0) generation. The immunological changes that were observed in the F(1) generation also appeared to be gender-specific.

Nerve growth factor and cholinergic CNS neurons studied in organotypic brain slices. Implication in Alzheimer's disease?

Nerve growth factor (NGF) is a potent growth factor for cholinergic neurons. The aim of the present study was to investigate if NGF affects cholinergic neurons of the basal nucleus of Meynert (nBM) in organotypic brain slices. In single nBM slices cholinergic neurons rapidly degenerated when incubated without NGF. The number of remaining neurons was rescued by NGF application at any time point. When nBM slices were co-cultured with a cortex slice the number of cholinergic neurons was significantly increased pointing to a trophic influence of the cortex. Incubation with acetylcholine precursors did not affect the survival of cholinergic neurons. There was no significant difference when postnatal day 3 or day 10 nBM slices were cultured. In conclusion, NGF is the most potent growth factor for cholinergic neurons and is a promising candidate for treating Alzheimers disease, however, the delivery of NGF to the brain must the solved.

Lipid-mediated in vivo gene transfer replaces the loss of choline acetyltransferase activity after unilateral fimbria-fornix aspiration

In Alzheimer's disease cholinergic neurons degenerate, resulting in loss of hippocampal acetylcholine. The fimbria-fornix aspiration is a well-known animal model mimicking hippocampal cholinergic deficiency. The aim of the present study was to use in vivo lipid-mediated gene transfer to introduce an expression vector coding for the acetylcholine synthesizing enzyme choline acetyltransferase into the hippocampus to replace the loss of enzyme activity after unilateral fimbria-fornix aspiration. Our data show that the lipid FuGene is useful to transfer DNA in vitro into 3T3 fibroblasts, C6 glioma cells, and primary astroglia and to express the respective enzyme. Lipid-mediated gene transfer in vivo resulted in a marked but transient expression of green fluorescent protein below the injection site peaking 5 days after the injection. Unilateral fimbria-fornix aspiration led to a marked reduction in the activity of choline acetyltransferase in the hippocampus, which was completely replaced 5 days after lipid-mediated gene transfer of the choline acetyltransferase vector. In conclusion, our data provide evidence that lipid-mediated gene transfer using FuGene is a useful tool to replace loss of choline acetyltranseferase activity in the hippocampus after fimbria-fornix aspiration; however, the lack of good gene transfer efficiency and the transient nature of expression limit its use for clinical applications.

Genistein modulates splenic natural killer cell activity, antibody-forming cell response, and phenotypic marker expression in F(0) and F(1) generations of Sprague-Dawley rats

The potential effects of the phytoestrogen genistein (GEN) on the immune system were evaluated in both F(0) (dams) and F(1) generations of Sprague-Dawley rats exposed to a soy-free diet containing low (L: 25 ppm), middle (M: 250 ppm), and high (H: 1250 ppm) levels of GEN. In dams, exposure to GEN from Gestation Day 7 to Postpartum Day 51 (totally 65 days) produced a significant increase in NK cell activity (M and H), while a decrease in the percentage of helper T cells (H). In F(1) males, exposure to GEN gestationally, lactationally, and through feed from Postnatal Days 22 to 64 (total 78 days) produced an increase in the relative weights (% body) of spleen (L and H) and thymus (L). Furthermore, exposure to GEN increased the number of splenic B cells (H), T cells (L, M, and H), and T-cell subsets (L, M, and H). Although GEN decreased the percentages of splenic NK cells (L, M, and H), no effect on the activity of NK cells was observed. In F(1) females, exposure to GEN produced a decrease in terminal body weight (H), with an increase in the relative weight of spleen (L, M, and H). Exposure to GEN also increased the number of splenic B cells (L), macrophages (L and M), T cells (H), helper T cells (L and H), and cytotoxic T cells (M and H). Additionally, exposure to GEN increased the percentages of T cells (M and H), helper T cells (H), and cytotoxic T cells (M and H). Moreover, the spleen IgM antibody-forming cell response to sheep red blood cells was enhanced (H), although the percentages of B cells were decreased (M and H). No effect on the activity of NK cells was observed; however, the percentages of splenic NK cells were decreased by GEN (L and H). In conclusion, these results demonstrate that exposure to GEN can modulate the immune responses in Sprague-Dawley rats. Furthermore, the sexual dimorphic effects of GEN in F(1) male and female rats suggest that there may be interactions between GEN and the responses modulated by sex hormones.

Differential regulation of chromogranin A, chromogranin B and secretogranin II in rat brain by phencyclidine treatment

Chromogranin A, chromogranin B and secretogranin II belong to the chromogranin family which consists of large protein molecules that are found in large dense core vesicles. Chromogranins are endoproteolytically processed to smaller peptides. This study was designed to elucidate the regulation of chromgranin expression by acute and subchronic phencyclidine administration. The behavioral syndrome produced by phencyclidine represents a pharmacological model for some aspects of schizophrenia [Jentsch and Roth (1999) Neuropsychopharmacology 20, 201-225]. Tissue concentrations of chromogranins were measured with specific radioimmunoassays. Alterations in secretogranin II gene expression were investigated by in situ hybridization. A single dose of phencyclidine (10mg/kg) led to a transient decrease in secretoneurin tissue levels in the prefrontal cortex after 4h followed by an increase in secretoneurin tissue levels after 12h. Repeated phencyclidine treatment (10mg/kg/day) for five days resulted in elevated secretoneurin levels in cortical areas whereas chromogranin A and chromogranin B tissue levels were unchanged. After the same treatment, a significant increase in the number of secretoneurin containing neurons was found in cortical layers II-III, and V-VI as revealed by immunocytochemistry. The increases in secretoneurin levels were paralleled by an increased number of secretogranin II messenger RNA containing neurons as well as by an increased expression of secretogranin II by individual neurons. The present study shows that secretoneurin II tissue concentration and secretogranin II messenger RNA expression is distinctly altered after acute and subchronic phencyclidine application. From these results we suggest that phencyclidine may induce synaptic alterations in specific brain areas and may contribute to a better understanding of synaptic dysfunction which may also occur in schizophrenia.

Refining the risk assessment of metal-contaminated soils

Determining the bioavailability of toxic metals (Pb, As, and Cd) in a diverse range of soils, allows scientifically derived data to dictate site-specific remedies to reduce the risk for sensitive human populations. Based on a series of dosing trials in a juvenile swine model, site-specific estimates of relative bioavailability of Pb in soil ranged from 3% to 86% compared to soluble lead acetate. Another experiment using a pregnant swine model revealed: 1) Pb accumulation in fetal tissues was 50% or more of maternal and; 2) pregnant females accumulated 2-to-4 times more lead in tissues than unbred females. Relative bioavailability results for arsenic- and cadmium-contaminated soils further support the view that soil metals are not always as well absorbed as soluble forms, therefore use of default toxicity factors for assessing human health risk may overestimate the hazard.

Nerve growth factor and glial cell line-derived neurotrophic factor restore the cholinergic neuronal phenotype in organotypic brain slices of the basal nucleus of Meynert

Loss of cholinergic neurons is found in the medial septum and nucleus basalis of Meynert in Alzheimer's disease. Recent observations suggest that cholinergic neurons down-regulate their phenotype and that growth factors may rescue cholinergic neurons. The aim of this study was to investigate whether cholinergic neurons of the basal nucleus of Meynert can be cultured in rat organotypic slices, and if nerve growth factor and glial cell line-derived neurotrophic factor can rescue the cholinergic phenotype. In the organotypic slices, glial cells, GABAergic and cholinergic neurons were visualized using immunohistochemistry. The number of cholinergic neurons was found to be very low in slices cultured without exogenous nerve growth factor. Analysis of nerve growth factor tissue levels by enzyme-linked immunosorbent assay revealed very low endogenous tissue levels. When slices were incubated with 100ng/ml nerve growth factor during the initial phase of culturing, a stable expression of choline acetyltransferase was found for up to several weeks. After eight weeks in culture with nerve growth factor or two to three weeks after nerve growth factor withdrawal, numbers of detected cholinergic neurons decreased. Neurons incubated with nerve growth factor displayed a significantly enlarged cell soma compared to neurons without growth factors. In cultures incubated for up to nine weeks, it was also found that glial cell line-derived neurotrophic factor was capable of restoring the cholinergic phenotype. The low-affinity p75 and high-affinity trkA receptors, as well as the glial cell line-derived neurotrophic factor receptor GFRalpha-1, could be visualized in slices using immunohistochemistry. In conclusion, it is shown that, in the axotomized organotypic slice model, the number of cholinergic neurons is decreased, but can be partly restored by nerve growth factor and glial cell line-derived neurotrophic factor.

Effects of the monoamine oxidase A inhibitor moclobemide on hippocampal plasticity in GR-impaired transgenic mice

A reduction in glucocorticoid receptor (GR) function leads to hippocampus-dependent allocentric spatial learning deficits, altered novelty exploration and disrupted hippocampal long-term potentiation (LTP) in transgenic mice expressing a GR antisense construct. After continuous long-term treatment of these mice with moclobemide (a reversible inhibitor of monoamine oxidase A), spatial navigation performance but not accuracy improved during initial acquisition. These changes were associated with a shift of the threshold for the induction of hippocampal LTP at low stimulation frequencies. Moreover, novel object exploration increased in both control and transgenic animals following long-term treatment with moclobemide. These findings open the possibility that antidepressants might improve hippocampal function under conditions of impaired stress hormone regulation, and that these drugs might in part act through this mechanism to attenuate cognitive deficiency in disorders such as depression.

Glial cell line-derived neurotrophic factor (GDNF) is a proliferation factor for rat C6 glioma cells: evidence from antisense experiments

Growth factors play an important role in proliferation and differentiation of malignant brain gliomas in humans. Glial cell line-derived neurotrophic factor (GDNF) has been shown recently to be highly expressed in human glioblastomas and in rat glial cell lines B49 and C6. The aim of the present study was to knockdown GDNF, its receptor GFR-alpha1, and the related family member persephin by using antisense oligonucleotides and to observe the effects on cell proliferation. To enhance cellular uptake into C6 glioma cells, 15-mer phosphorothioate oligonucleotides were complexed with the cationic lipid Lipofectamine. The complex was applied for 3 x 12 hours to C6 glioma cells, and cells were allowed to recover for 24 hours after each transfection and then analyzed. This protocol markedly reduced GDNF and GFR-alpha1 protein levels in C6 glioma cells compared with control oligonucleotides. Knockdown of C6 cells with GDNF and GFR-alpha1 but not with persephin antisense oligonucleotides significantly decreased the number of C6 glioma cells and also inhibited the incorporation of bromodeoxyuridine as a sign of reduced DNA synthesis. In conclusion, it is shown that GDNF but not persephin is a potent proliferation factor for rat glioma cells. Knockdown of GDNF using antisense oligonucleotides complexed with lipids as carriers may be useful in gene therapeutic approaches in vitro and possibly also in vivo.

Strike a balance with decentralized housekeeping

Housekeeping staff join patient-care teams to improve patient care, but the transition can cause problems of its own. Read how one hospital minimized the negative effects and improved staff productivity and patient satisfaction.

Chronic repetitive transcranial magnetic stimulation enhances c-fos in the parietal cortex and hippocampus

Repetitive transcranial magnetic stimulation (rTMS) is a novel non-invasive method with anti-depressant properties. However, the mechanism of activation on the cellular level is unknown. Twelve hours after the last chronic rTMS treatment (14 days, once per day, 20 Hz, 10 s, 75% machine output, the transcription factor c-fos was markedly increased in neurons in layers I-IV and VI of the parietal cortex and in few scattered neurons in the hippocampus of Sprague-Dawley rats. The cortical activation was not blocked by the NMDA antagonist MK-801. The increase of c-fos was not paralleled by an increased glial response and activation of cortical growth factors. Thus, it is concluded that chronic rTMS differentially activates parietal cortical layers and this might be involved in mediating anti-depressant activity in other brain areas.

On-line techniques for perfluorochemical vapor sampling and measurement

The authors developed a compact gas sampling and perfluorochemical (PFC) measuring system for use in total and partial liquid ventilation systems, based on a precision two-thermistor thermal detector (TD). They describe the sensitivity and linearity of their on-line method for PFC analysis of expired gases and show how it may be used in partial liquid ventilation studies for determining PFC saturation and loss. Gas is sampled for a short time from a breathing circuit through a heated tube at a selectable point in the breathing cycle. Inspiration is sensed by a pressure transducer. The sample of gas is pulled into the heated (48 degrees C) thermistor chamber by suction and held there while the cooling effect of the vapor changes the thermistor temperature. Dry air in another chamber affects a second thermistor, and the difference of these responses is amplified. The raw signal is corrected for the effects of varying O2 levels by a fuel cell. This signal is sampled and held and displayed on a front panel display. Calibration is performed in percentage saturation at 37 degrees C using the PFC in use at that temperature, or another standard such as O2. In-vitro testing showed a linear response in the thermal detector device (R2 = 0.99) over the range of vapor pressures tested (0-14) mmHg) and was reproducible to within 3%. When electronically corrected for changes in O2 concentration, there was less than a 2% change in PFC saturation. The TD responses to CO2 (R2 = 0.99) and water vapor (R2 = 1.0) were linear and approximately equal and opposite over the normal operating ranges of expired gases. In-vivo results in rabbits showed a significant (R2 = 0.73; p < 0.01) correlation between the auto-sampler and manual collection modes for determination of PFC in expired gas.

Disrupted allocentric but preserved egocentric spatial learning in transgenic mice with impaired glucocorticoid receptor function

Spatial and non-spatial learning of mice with an incorporated antisense RNA complementary to a fragment of cDNA coding for the glucocorticoid receptor (GR) were evaluated in allocentric and egocentric radial maze and water maze tasks, and in spontaneous object recognition and sensorimotor learning paradigms. Mice with impaired GR function did not acquire two maze paradigms based on allocentric spatial navigation, radial maze non-matching to position and water maze spatial discrimination learning. Comparison of performance in spaced and massed trials indicated that this may be due to a general inability to store information into allocentric reference memory or in retrieval processes. However, both groups of animals learned the rules of an egocentric radial maze task at similar rates and there was no difference in their ability to recognise objects once animals had equal opportunity to explore the sample objects. Sensorimotor performance was impaired in transgenic animals, but it is suggested that this is due to non-specific factors rather than to disrupted sensorimotor learning per se. These results are consistent with a disruption of hippocampal function. Histological examination of the hippocampus revealed no obvious structural abnormalities in transgenic animals. Therefore, the data suggest that functional underactivity of GRs at the level of the hippocampus induces a deficit in allocentric navigation while sparing egocentric navigation and object recognition.

Relative contribution of calories from dietary fat, carbohydrate, and fiber in the promotion of DMBA-induced mammary tumors in Sprague-Dawley rats

It is well known that caloric restriction inhibits, whereas excess calories promote, mammary tumorigenesis in rats. However, the relative contribution to carcinogenesis by calories derived from fat or from carbohydrate are not well established. To determine the relative effects of calories from fat or from carbohydrate, as well as any interaction of dietary fiber on the promotion of 7,12-dimethylbenz[a]anthracene-induced mammary tumors, we fed isocalorically nine diets containing different ratios of fat, carbohydrate, and fiber to female Sprague-Dawley rats treated with 7,12-dimethylbenz[a]anthracene (30/group). Under conditions of isocaloric consumption, at or near ad libitum feeding, calories from dietary fat had approximately twofold greater promoting effect on final body weight and tumor incidence than calories derived from dietary carbohydrate. Dietary fiber had an inhibitory effect on tumor development, but the effect was evident only in the high-fat groups. Logistic regression analysis of tumor incidence gave beta-coefficient estimates for the relative effects of fat, carbohydrate, and fiber of 0.866, 0.189, and -4.281, respectively. Time-to-tumor analysis by the Weibull model indicated beta-estimates of 3.016, 3.324, and 5.825 for dietary fat, carbohydrate, and fiber, respectively, indicating that fat shortens and fiber increases the length of time to tumor. The statistical model derived from these results also indicates a significant synergistic interaction of dietary fat and carbohydrate on final body weight and tumor incidence.

Western blot analysis of the immune response to Candida albicans antigens in 391 long-term intensive care patients

The aim of this study was to determine, using Western blot, the prevalence of anti-Candida albicans antibodies in long-term intensive care patients and to characterize specific immune responses that may only occur in patients with invasive candidosis. A total of 1751 serum samples from 391 patients of a German multicentre study, which was designed to determine the incidence of systemic candidosis, was examined. Significantly enhanced antibody production against specific antigens was observed in several subgroups of patients, i.e. those with underlying disease of the pancreas (29 kDa, P = 0.006), cholecystolithiasis (47 kDa, P = 0.029), gastrointestinal tract disease (47 kDa, P = 0.03), steroid therapy (58 kDa, P = 0.02), thrush (58 kDa, P = 0.032), urogenital infection (58 kDa, P = 0.034), Candida antigen titre > or = 1:4 (58 kDa, P = 0.002) and positive fungal culture (36 kDa, P = 0.033) and those who had died (36 kDa, P = 0.011). In contrast to earlier publications, an immune response against the 29 and 47 kDa antigens was relatively common among long-term intensive care patients (37% and 70% antibody positive respectively). A single antigen that provided satisfactory sensitivity and specificity for the discrimination between fungal infection and no fungal infection or between superficial and invasive fungal infection was not identified in this study.

Dietary restriction modulated carcinogen-DNA adduct formation and the carcinogen-induced DNA strand breaks

Dietary restriction (DR) alters the activities of hepatic drug metabolizing enzymes and modulates the formation of carcinogen-DNA adducts in carcinogen treated animals. Our previous results showed that a 40% restriction of diet (60% of ad libitum (AL) food consumption) reduced the hepatic metabolic activation of aflatoxin B1 (AFB1) but increased the activation of benzo[a]-pyrene (BaP) in both rats and mice. In this study, the focus was directed toward the levels of carcinogen-DNA adducts formation and the carcinogen-induced DNA strand breaks in mouse kidney and liver DNA. DR significantly inhibited both AFB1-DNA adduct formation and AFB1-induced DNA strand breaks in kidney DNA of mice that received a single dose of [3H]AFB1 (5 mg/kg). The levels of AFB1-DNA adduct formation in mouse kidney DNA correlated well with increased AFB1-induced DNA strand breaks. The correlation between the levels of AFB1-DNA-adducts formed and DNA strand breaks in kidney DNA of DR-mice was less linear than between its AL-counterpart suggesting that other factors, such as different rates of DNA repair, may be involved. In addition, DR enhanced hepatic BaP- and 6-nitrochrysene (6-NC)-DNA adduct formation in the mice treated with BaP and 6-NC, respectively. The formation of the specific BaP-adduct, 10-(N2-deoxyguanosinyl)-7,8,9-trihydroxy-7,8,9,10-tetrahydro-BaP (N2-dG-BaP), in mouse liver was proportional to the dose, and was compatible to the BaP-induced DNA strand breaks affected by DR. The enhancement of the total 6-NC-DNA adduct formation in DR-mouse was also in correlation with the increased 6-NC-induced DNA strand breaks. The activity of mouse liver microsomal nitro-reductase increased by 2-fold in response to DR indicating that the nitroreduction may contribute to the increase of the metabolic activation of 6-NC. Our present results indicate that the effect of DR on the carcinogen activation is dependent upon the DR-modulated carcinogen metabolizing enzyme activities.

Dietary nucleotides: effects on cell proliferation following partial hepatectomy in rats fed NIH-31, AIN-76A, or folate/methyl-deficient diets

The requirement of a number of tissues for dietary nucleotides could explain some of the differences observed in animals fed natural ingredient diets vs. those fed purified diets lacking a source of dietary nucleotides. Lack of dietary nucleotides is exacerbated in animals fed folate- or methyl-deficient semipurified diets, in which both salvage and folate-dependent de novo synthetic pathways are diminished. We examined hepatocyte proliferation following partial hepatectomy in weanling male Fischer-344 rats fed natural ingredient NIH-31 diet, nucleotide-free purified AIN-76A diet or a basal diet similar to AIN-76A but deficient in the methyl donors folate, choline and methionine. Additional groups were fed AIN-76A or folate/methyl-deficient diets supplemented with 0.25% yeast RNA. Compared with NIH-31, AIN-76A increased dUMP/dTTP ratios, reduced the mitotic index (MI) and increased the ratio of proliferating cell index (PCI) to mitotic cells, an indication that hepatocytes were delayed in S-phase. Addition of yeast RNA to AIN-76A reversed (by approximately 50%) the effects of AIN-76A on dUMP/dTTP and cell proliferation. A folate/methyl-deficient diet also produced an increased dUMP/dTTP ratio and markedly reduced the MI, increasing the PCI/MI, which suggested even further delay of cells in S-phase. Addition of yeast RNA to the folate/methyl-deficient diet was effective in significantly reversing the effects of folate/methyl deficiency.

Neonatal endotracheal tubes: variation in airway resistance with different perfluorochemical liquids

To evaluate the effect of the physical properties of density and viscosity on airway resistance, three perfluorochemical fluids (PFCs) were used: FC-75, Liquivent, and APF-140. Using two different endotracheal tubes (ETT) (3.0mm ID and 4.0mm internal diameter (ID)), the three fluids were studied at steady state flow conditions over a range that approximated peak flow required for liquid ventilation of neonatal lambs (0.005-0.02 l/sec). The slope of airway resistance (Raw)-flow curves and absolute values of Raw for the 3 PFC liquids were higher for the 3.0 ETT compared to the 4.0 ETT. The 3.0 ETT demonstrated resistance changes that were dependent on flow, density and viscosity. The 4.0 ETT showed a resistance-flow relationship that was relatively less dependent on flow, density and viscosity.

[Perforation of gastroduodenal ulcer: a risk analysis]

In 90 patients who, between 1.1.1986 and 31.12.1991, underwent surgery for a perforated gastric/duodenal ulcer, the importance of age, sex, ulcer history, ulcer site, free/covered perforation, extent of peritonitis, duration of history and the pre-operative risk assessment (ASA classification) was analysed with respect to the risk of dying of the perforated ulcer. The univariate analysis showed the following to be prognostically relevant factors: time interval between onset of acute symptoms and surgery (less than or equal to 24 hours: mortality rate 12%, greater than 24 hours: mortality rate 21%; p = 0.006); physical status of the patient as reflected in the ASA category prior to surgery (mortality: ASA II 0%, ASA III 8%, ASA IV 32%; p = 0.009), and the presence of a spontaneous pneumoperitoneum (free perforation 21% mortality, covered perforation 5% mortality; p = 0.049). Investigation of the overall influence of the univariate relevant factors in the logistic model showed a relative risk of 4.9 for duration of history, and of 5.4 for the ASA classification. The mortality risk for a patient who is operated on more than 24 hours after onset of the acute symptoms is 4.9 times that of a patient operated on within 24 hours. In the ASA classification, the mortality risk increases by 5.4 from one category to the next higher one.

[Hematobilia--a rare complication after traumatic liver rupture]

Hematobilia is a rare complication after traumatic liver injury and has a high mortality. Clinical signs are hyperbilirubinemia and increase of bile acids in serum by rarely increased liver enzymes. Pathophysiologically there is a connection between bile duct system and liver veins. To determine the diagnosis giving rise to the clinical signs, after abdominal ultrasonography and computed tomography the ERCP seems to be the most suitable method. The treatment of hematobilia is not necessarily operative; a successful conservative therapy is also possible.

Aluminum-altered membrane dynamics in human red blood cell white ghosts

Fluorescence polarization of the hydrophobic membrane probe 1,6-diphenyl hexatriene was used to investigate alterations in membrane dynamics caused by micromolar concentrations of aluminum. Metal titration onto resealed white ghost membranes showed a progressive increase in steady-state fluorescence anisotropy of the probe in the presence of aluminum which was twice the value obtained upon titration of calcium. As calculated from steady-state fluorescence data in the presence and absence of 20 microM aluminum, a temperature dependent lipid order parameter indicated increased lipid packing. Motional dynamics of the probe molecule on the nanosecond time scale showed severe constraints in the presence of 20 microM aluminum as indicated by decreased rotational rate, decreased cone angle, and increased values of time resolved limiting anisotropy. Physiological consequences of altered membrane dynamics are also discussed.

Aluminum-induced conformational changes in calmodulin alter the dynamics of interaction with melittin

Studies were undertaken to examine the impact of aluminum-induced structural changes in bovine brain calmodulin on the protein's interface region with melittin, a model for calmodulin's target enzymes. Both steady-state and time-dependent fluorescence characteristics of the single tryptophanyl residue of melittin were employed to derive information on aluminum-related changes in the fluorophore's microenvironment. In the presence of stoichiometric amounts of aluminum ions, calmodulin's target region with melittin appears to be more polar than that with aluminum absent. As a result, upon association of melittin with aluminum-calmodulin, the enhancement of helical arrays is less pronounced. The fluorophore's average microenvironment also is modified such that its apparent lifetime is shortened when aluminum is present. In the presence of aluminum ions, the solvation structure of calmodulin is possibly changed, which may be unfavorable for a proper fit between calmodulin and target proteins.