Nicotinic Autoreceptors Mediating Enhancement of Acetylcholine Release Become Operative in Conditions of "Impaired" Cholinergic Presynaptic Function

Abstract: The existence in the mammalian CNS of release-inhibiting muscarinic autoreceptors is well established. In contrast, few reports have focused on nicotinic autoreceptors mediating enhancement of acetylcholine (ACh) release. Moreover, it is unclear under what conditions the function of one type of autoreceptor prevails over that of the other. Rat cerebrocortex slices, prelabeled with [³H]choline, were stimulated electrically at 3 or 0.1 Hz. The release of [³H]ACh evoked at both frequencies was inhibited by oxotremorine, a muscarinic receptor agonist, and stimulated by atropine, a muscarinic antagonist. Nicotine, ineffective at 3 Hz, enhanced [³H]ACh release at 0.1 Hz; mecamylamine, a nicotinic antagonist, had no effect at 3 Hz but inhibited [³H]ACh release at 0.1 Hz. The cholinesterase inhibitor neostigmine decreased [³H]ACh release at 3 Hz but not at 0.1 Hz; in the presence of atropine, neostigmine potentiated [³H]ACh release, an effect blocked by mecamylamine. In synaptosomes depolarized with 15 mM KCI, ACh inhibited [³H]ACh release; this inhibition was reversed to an enhancement when the external [Ca²⁺] was lowered. The same occurred when, at 1.2 mM Ca²⁺, external [K⁺] was decreased. Oxotremorine still inhibited [³H]ACh release at 0.1 mM Ca²⁺. When muscarinic receptors were inactivated with atropine, the K⁺ (15 mM)-evoked release of [³H]ACh (at 0.1 mM Ca²⁺) was potently enhanced by ACh acting at nicotinic receptors (EC₅₀? 0.6 µM). In conclusion, synaptic ACh concentration does not seem to determine whether muscarinic or nicotinic autoreceptors are activated. Although muscarinic autoreceptors prevail under normal conditions, nicotinic autoreceptors appear to become responsive to endogenous ACh and to exogenous nicotinic agents under conditions mimicking impairment of ACh release. Our data may explain in part the reported efficacy of cholinesterase inhibitors (and nicotinic agonists) in Alzheimer's disease.     

Smoking Is Associated with More Abdominal Fat in Morbidly Obese Patients

IntroductionWhile the association between cigarette smoking and abdominal fat has been well studied in normal and overweight patients, data regarding the influence of tobacco use in patients with morbid obesity remain scarce. The aim of this study is to evaluate body fat distribution in morbidly obese smokers.MethodsWe employed a cross-sectional study and grouped severely obese patients (body mass index [BMI] >40 kg/m² or >35 kg/m² with comorbidities) according to their smoking habits (smokers or non-smokers). We next compared the anthropometrical measurements and body composition data (measured by electric bioimpedance) of both groups. We analyzed the effect of smoking on body composition variables using univariate and multiple linear regression (MLR); differences are presented as regression coefficients (b) and their respective 95% confidence intervals.ResultsWe included 536 morbidly obese individuals, 453 (84.5%) non-smokers and 83 (15.5%) smokers. Male smokers had a higher BMI (b=3.28 kg/m², p=0.036), larger waist circumference (b=6.07 cm, p=0.041) and higher percentage of body fat (b=2.33%, p=0.050) than non-smokers. These differences remained significant even after controlling for confounding factors. For females, the only significant finding in MLR was a greater muscle mass among smokers (b=1.34kg, p=0.028). No associations were found between tobacco load measured in pack-years and anthropometric measures or body composition.DiscussionPositive associations between smoking and BMI, and waist circumference and percentage of body fat, were found among male morbidly obese patients, but not among females. To the best of our knowledge, this study is the first investigation of these aspects in morbidly obese subjects. We speculate that our findings may indicate that the coexistence of morbid obesity and smoking helps to explain the more serious medical conditions, particularly cardiovascular diseases and neoplasms, seen in these patients.     

Draft Genome Sequence of the Hydrocarbon-Degrading and Emulsan-Producing Strain Acinetobacter venetianus RAG-1T

We report the draft genome sequence of Acinetobacter venetianus strain RAG-1(T), which is able to degrade hydrocarbons and to synthesize a powerful biosurfactant (emulsan) that can be employed for oil removal and as an adjuvant for vaccine delivery. The genome sequence of A. venetianus RAG-1(T) might be useful for bioremediation and/or clinical purposes.     

An in vitro demonstration of peroxisome proliferation and increase in peroxisomal β-oxidation system mRNAs in cultured rat hepatocytes treated with ciprofibrate

Using the normal adult rat hepatocytes, plated on rat tail collagen-coated dishes and fed a chemically defined medium, we demonstrate here that ciprofibrate at 0.1 mM concentration, increases significantly the mRNA levels of fatty acyl-CoA oxidase, enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase bifunctional protein, and thiolase (the three enzymes of the β-oxidation system), and causes peroxisome proliferation. Increase in mRNA levels of these genes was evident within 1 h and was maximal 24 h after the addition of ciprofibrate. In hepatocytes cultured in the absence of ciprofibrate, the basal levels of these enzymes were low and further declined with time. Concomitant treatment of hepatocytes with cycloheximide did not inhibit or superinduce the mRNA levels, indicating that this induction may represent a primary (direct) effect of this compound on the expression of these genes and does not apparently involve short-lived repressor protein(s).     

Exploring interaction of beta-amyloid segment (25-35) with membrane models through paramagnetic probes.

The accumulation of beta-amyloid peptides into senile plaques is one of the hallmarks of Alzheimer's disease (AD). There is mounting evidence that the lipid matrix of neuronal cell membranes plays an important role in the beta-sheet oligomerization process of beta-amyloid. Abeta(25-35), the sequence of which is GSNKGAIIGLM, is a highly toxic segment of amyloid beta (Abeta)-peptides, which forms fibrillary aggregates. In the present work, two spin-labelled Abeta(25-35) analogues containing the nitroxide group of the amino acid TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) as a paramagnetic probe at the N- or the C-terminus of the peptide sequence, respectively, were synthesized in order to investigate the peptide-membrane interaction. The orientation and associated changes of the peptide conformation in the presence of different artificial membrane models (micelles, liposomes) were evaluated by electron paramagnetic resonance and circular dichroism techniques. The results of this study allowed us to propose a model in which the C-terminal portion of the peptide is highly associated to the membrane, while the N-terminal part extends into the aqueous phase with occasional contacts with the lipid head-group region. Interestingly, the interaction of the C-terminal portion of the peptide is particularly enhanced in the presence of sodium dodecyl sulfate (SDS) molecules.     

Plasma membrane of Beta vulgaris storage root shows high water channel activity regulated by cytoplasmic pH and a dual range of calcium concentrations

Plasma membrane vesicles isolated by two-phase partitioning from the storage root of Beta vulgaris show atypically high water permeability that is equivalent only to those reported for active aquaporins in tonoplast or animal red cells (Pf=542 microm s(-1)). The values were determined from the shrinking kinetics measured by stopped-flow light scattering. This high Pf was only partially inhibited by mercury (HgCl2) but showed low activation energy (Ea) consistent with water permeation through water channels. To study short-term regulation of water transport that could be the result of channel gating, the effects of pH, divalent cations, and protection against dephosphorylation were tested. The high Pf observed at pH 8.3 was dramatically reduced by medium acidification. Moreover, intra-vesicular acidification (corresponding to the cytoplasmic face of the membrane) shut down the aquaporins. De-phosphorylation was discounted as a regulatory mechanism in this preparation. On the other hand, among divalent cations, only calcium showed a clear effect on aquaporin activity, with two distinct ranges of sensitivity to free Ca2+ concentration (pCa 8 and pCa 4). Since the normal cytoplasmic free Ca2+ sits between these ranges it allows for the possibility of changes in Ca2+ to finely up- or down-regulate water channel activity. The calcium effect is predominantly on the cytoplasmic face, and inhibition corresponds to an increase in the activation energy for water transport. In conclusion, these findings establish both cytoplasmic pH and Ca2+ as important regulatory factors involved in aquaporin gating.     

Estimating the infectivity of CCR5-tropic simian immunodeficiency virus SIV(mac251) in the gut

CD4+ T-cell depletion during acute human immunodeficiency virus infection occurs predominantly in the gastrointestinal mucosa. Using experimental data on SIV(mac251) viral load in blood and CD4+ T cells in the jejunum, we modeled the kinetics of CD4+ T-cell infection and death and estimated the viral infectivity. The infectivity of SIV(mac251) is higher than previously estimated for SHIV89.6P infection, but this higher infectivity is offset by a lower average peak viral load in SIV(mac251). Thus, the dynamics of target cell infection and death are remarkably similar between a CXCR4- and a CCR5-tropic infection in vivo.     

Production of a thermophilic maltooligosyl-trehalose synthase in <Emphasis Type="Italic">Lactococcus lactis</Emphasis>

The thermoacidophilic archaeon Sulfolobus solfataricus MT4 encodes a maltooligosyltrehalose synthase (MTS), that catalyzes an intramolecular transglycosylation process converting the glycosidic linkages at the reducing end of dextrins from alpha-1,4 into alpha-1,1. In this research the gene encoding MTS was cloned and expressed in Lactococcus lactis NZ9000 using the so-called NICE system. Growth conditions of the recombinant strain were optimized in flask experiments in relation to enzyme production. Batch experiments in 2 L-fermenters were performed on the best identified semidefined medium and 256 U L(-1) of recombinant MTS were produced. Purified recombinant MTS shows its optimal activity at 70 degrees C and pH 5.5, prefers maltoheptaose and maltohexaose as substrates, and demonstrates minimal side hydrolytic activity.