Ca-dependence of diastolic properties of cardiac sarcomeres: involvement of titin

The stiffness of the sarcomeres was studied during the diastolic interval of 18 stimulated (0.5 Hz) cardiac trabeculae of rat (pH 7.4; temperature = 25°C). Sarcomere length (SL) and force (F) were measured using, respectively, laser diffraction techniques (resolution: 4 nm) and a silicon strain gauge (resolution: 0.63 μN). Sinusoidal perturbations (frequency = 500 Hz) were imposed to the length of the preparation. The stiffness was evaluated from the corresponding F and SL sinusoids by analysis of both signals together either in the time domain or in the frequency domain. A short burst (duration = 30 ms) of sinusoidal perturbations was repeated at 5 predetermined times during diastole providing 5 measurements of stiffness during the time interval separating two twitches. These measurements revealed that stiffness increases by 30% during diastole, while a simultaneous expansion of the sarcomeres (amplitude = 10-60 nm) was detected. Measurements of the fluorescence of fura-2 under the same conditions revealed a continuous exponential decline of [Ca²⁺]_i from 210 to 90 nM (constant of time 300 ms) during diastole. In order to test the possibility that the increase of sarcomere stiffness and the decline of [Ca²⁺]_i were coupled during diastole of intact trabeculae, we studied the effect of different free Ca²⁺-concentrations ([Ca²⁺]) between 1 and 430 nM on sarcomere stiffness in rat cardiac trabeculae skinned by saponin (n = 17). Stiffness was studied using 500 Hz sinusoidal perturbations of muscle length (ML). We found that, below 70 nM, the stiffness was independent of [Ca²⁺]; between 70 and 200 nM, the stiffness declined with increase of [Ca²⁺]; above 200 nM, the stiffness increased steeply with [Ca²⁺]. The data fitted accurately to the sum of two sigmoids (Hill functions): (1) at [Ca²⁺] < 200 nM the stiffness decreased with [Ca²⁺] (EC₅₀ = 160 ± 13 nM; n = −2.6±0.7) and (2) at [Ca²⁺] > 200 nM, stiffness increased with [Ca²⁺] (EC₅₀ = 3.4±0.3 μM; n = 2.1±0.2) due to attachment of cross-bridges. From these results, it was possible to reproduce accurately the time course of diastolic stiffness observed in intact trabeculae and to predict the effect on stiffness of a spontaneous elevation of the diastolic [Ca²⁺]. Identical stiffness measurements were performed in 4 skinned preparations exposed to a cloned fragment of titin (Ti I-II) which has been shown to exhibit a strong interaction with F-actin in vitro. It was anticipated that Ti I-II would compete with endogenous titin for the same binding site on actin in the I-band. Below 200 nM, Ti I-II (2 μM) eliminated the Ca²⁺-dependence of stiffness. These results are consistent with the hypothesis that the Ca²⁺-sensitivity of the sarcomeres at [Ca²⁺] < 200 nM, i.e. where the myocytes in intact muscle operate during diastole, involves an association between titin molecules and the thin filament.     

Inter and intra-species-related differences in the regulation of the cardiac autonomic system

The heart rate response to isoproterenol (HR-Iso), density and affinity (k_d) of β-adrenergic (β-AR) and muscarinic (M₂) receptors were compared among three rodents with different generation-life histories of confinement and of high altitude exposure. The European guinea pig (Cavia porcellus) (EGp), a laboratory animal that arrived in Europe after the Spanish Conquest of South America and the Peruvian guinea pig (C. porcellus) (PGp), a semi-wild animal that came from the altiplano to sea level at least 25 generations ago, were used for intra-species comparison. Wistar rats (WR) were used for inter-species comparison as representative of a typical sea level laboratory animal. The HR-Iso was lower in EGp than in the PGp. The PGp showed the highest β-AR density (P<0.0005) and the highest β-AR k_d values (P<0.0005) when compared to both EGp and WR groups (β-AR B_max (fmol mg⁻¹ prot), WR, 19±4; Egp, 34±10; PGp, 74±15. β-AR k_d (pM), WR, 24±10; Egp, 17±7; PGp, 39±14). In contrast, PGp showed lower M₂ receptor density values than the EGp (P<0.0005). The WR had the highest M₂ receptor densities (M₂ B_max (fmol mg⁻¹ prot), WR, 188±15; Egp, 147±9; PGp, 118±6 and M₂ k_d (pM), WR, 65±12; Egp, 67±6; PGp, 92±2). The inter and intra-species differences found may be related to their respective history of confinement rather than to their history of exposure to high altitude.     

ACETYLCHOLINESTERASE OF RAT SYMPATHETIC GANGLION: MOLECULAR FORMS, LOCALIZATION AND EFFECTS OF DENERVATION

Abstract— In sucrose gradient centrifugation, acetylcholinesterase (AChE, EC 3.1.1.7.) from the rat superior cervical ganglion (SCG) has been found to contain four molecular forms, characterized by their sedimentation coefficients (4 S, 6.5 S, 10 S and 16 S). Homogenization of the ganglia in various media showed that the 4 S enzyme was readily solubilized in water whereas solubilization of the 6.5 S and 10 S forms was quantitative only in media containing Triton X-100. In order to solubilize the 16 S form, high concentrations of salt (NaCl 1 M) and detergent had to be present. AChE analysed by non-denaturing polyacrylamide gel electrophoresis separated into five bands. Although both distribution patterns were stable, i.e. each form or band preserved its characteristic sedimentation or electrophoretic migration when reanalysed, there was no 1:1 correlation between the forms isolated by sedimentation and the bands obtained by electrophoresis: one band might contain more than one form of enzyme, and conversely one form gave rise to several bands. It was therefore impossible to derive molecular weights from electrophoretic migration in non-denaturing gels. However, it could be shown that the results obtained by both methods of analysis were consistent. Acetylcholinesterase from other nervous structures was analysed: in pre- and postganglionic nerves, the main forms were 10 S and 6.5 S, with a small proportion of 4 S; the 16 S form was not detected. In other sympathetic ganglia, the distribution of forms was identical to that of the superior cervical ganglion. In rachidian ganglia, no 16 S form could be found. Following the section of the preganglionic nerve, the acetylcholinesterase activity of the superior cervical ganglion decreased by 50% in 3 days, and then rose again to about 80% of its original value after 2 weeks. These effects mainly reflected variations in the major 4 S and 10 S forms. The 16 S form, in contrast to its disappearance from denervated muscles, increased transiently during the first 2 weeks after denervation, reaching about twice its original activity. A concomitant cytochemical study of normal and denervated ganglia showed that after preganglionic denervation, AChE localized in the sympathetic neurones decreased markedly and remained low even during the recovery phase. During this period a cholinesterasic activity appeared in the perineuronal glia. Controls established that the enzyme synthetized in the glia is AChE.     

Galactomannoproteins of Aspergillus fumigatus

Galactofuranose-containing molecules have been repeatedly shown to be important antigens among human fungal pathogens, including Aspergillus fumigatus. Immunogenic galactofuran determinants have been poorly characterized chemically, however. We reported here the characterization of two glycoproteins of A. fumigatus with an N-glycan containing galactofuranose. These proteins are a phospholipase C and a phytase. Chemical characterization of the N-glycan indicates that it is a mixture of Hex(5-13)HexNAc(2) oligosaccharides, the major molecular species corresponding to Hex(6-8)HexNAc(2). The N-glycan contained one galactofuranose unit that was in a terminal nonreducing position attached to the 2 position of Man. This single terminal nonreducing galactofuranose is essential for the immunoreactivity of the N-glycans assessed either with a monoclonal antibody that recognizes a tetra-beta-1,5-galactofuran chain of galactomannan or with Aspergillus-infected patient sera.     

Expression and purification of untagged full-length HCV NS5B RNA-dependent RNA polymerase

The NS5B encoded by the hepatitis C virus genome is a RNA-dependent RNA polymerase essential to viral replication. The entire NS5B protein contains a catalytic domain followed by a regulatory motif and a membrane-anchor domain at its C-terminus. Reported here is the molecular cloning and expression of the full-length NS5B polymerase (NS5B-FL) in bacterial cells as a non-fusion protein. The non-tagged NS5B-FL was purified to homogeneity using sequential chromatographic columns and its identity was confirmed using anti-NS5B peptide antibodies and amino acid sequencing. Purified NS5B-FL demonstrated RNA-dependent RNA polymerase activity and was able to replicate a HCV RNA genome fragment through both copy-back and de novo mechanisms. Its biochemical properties were further characterized in comparison with a truncated form of NS5B polymerase with a deletion of 51 residues from its C-terminus.     

In vitro activation of murine DRG neurons by CGRP-mediated mucosal mast cell degranulation

Upregulation of CGRP-immunoreactive (IR) primary afferent nerve fibers accompanied by mastocytosis is characteristic for the Schistosoma mansoni-infected murine ileum. These mucosal mast cells (MMC) and CGRP-IR fibers, which originate from dorsal root (DRG) and nodose ganglia, are found in close apposition. We examined interactions between primary cultured MMC and CGRP-IR DRG neurons in vitro by confocal recording of intracellular Ca(2+) concentration ([Ca(2+)](i)). The degranulatory EC(50) for the mast cell secretagogue compound 48/80 (C48/80; 10 microg/ml) and the neuropeptides CGRP (2.10(-8) M) and substance P (SP; 3.10(-8) M) were determined by measurement of extracellular release of the granule chymase, mouse mast cell protease-1. Application of C48/80 (10 microg/ml) and CGRP and SP (both 10(-7) M) to Fluo-4-loaded MMC induced a transient rise in [Ca(2+)](i) after a lag time, indicative of mast cell degranulation and/or secretion. The CGRP response could be completely blocked by pertussis toxin (2 microg/ml), indicating involvement of G(i) proteins. Application of MMC juice, obtained by C48/80 degranulation of MMC, to Fluo-4-loaded DRG neurons induced in all neurons a rise in [Ca(2+)](i), indicative of activation. Degranulation of MMC by C48/80 in culture dishes containing Fluo-4-loaded DRG neurons also caused activation of the DRG neurons. In conclusion, these results demonstrate a bidirectional cross-talk between cultured MMC and CGRP-IR DRG neurons in vitro. This indicates that such a communication may be the functional relevance for the close apposition between MMC and CGRP-IR nerve fibers in vivo.     

Genome-wide linkage scan reveals multiple susceptibility loci influencing lipid and lipoprotein levels in the Quebec Family Study

A genome-wide linkage study was performed to identify chromosomal regions harboring genes influencing lipid and lipoprotein levels. Linkage analyses were conducted for four quantitative lipoprotein/lipid traits, i.e., total cholesterol, triglyceride, HDL-cholesterol (HDL-C), and LDL-C concentrations, in 930 subjects enrolled in the Québec Family Study. A maximum of 534 pairs of siblings from 292 nuclear families were available. Linkage was tested using both allele-sharing and variance-component linkage methods. The strongest evidence of linkage was found on chromosome 12q14.1 at marker D12S334 for HDL-C, with a logarithm of the odds (LOD) score of 4.06. Chromosomal regions harboring quantitative trait loci (QTLs) for LDL-C included 1q43 (LOD = 2.50), 11q23.2 (LOD = 3.22), 15q26.1 (LOD = 3.11), and 19q13.32 (LOD = 3.59). In the case of triglycerides, three markers located on 2p14, 11p13, and 11q24.1 provided suggestive evidence of linkage (LOD > 1.75). Tests for total cholesterol levels yielded significant evidence of linkage at 15q26.1 and 18q22.3 with the allele-sharing linkage method, but the results were nonsignificant with the variance-component method. In conclusion, this genome scan provides evidence for several QTLs influencing lipid and lipoprotein levels. Promising candidate genes were located in the vicinity of the genomic regions showing evidence of linkage.     

Copper-adapted Suillus luteus, a symbiotic solution for pines colonizing Cu mine spoils

Natural populations thriving in heavy-metal-contaminated ecosystems are often subjected to selective pressures for increased resistance to toxic metals. In the present study we describe a population of the ectomycorrhizal fungus Suillus luteus that colonized a toxic Cu mine spoil in Norway. We hypothesized that this population had developed adaptive Cu tolerance and was able to protect pine trees against Cu toxicity. We also tested for the existence of cotolerance to Cu and Zn in S. luteus. Isolates from Cu-polluted, Zn-polluted, and nonpolluted sites were grown in vitro on Cu- or Zn-supplemented medium. The Cu mine isolates exhibited high Cu tolerance, whereas the Zn-tolerant isolates were shown to be Cu sensitive, and vice versa. This indicates the evolution of metal-specific tolerance mechanisms is strongly triggered by the pollution in the local environment. Cotolerance does not occur in the S. luteus isolates studied. In a dose-response experiment, the Cu sensitivity of nonmycorrhizal Pinus sylvestris seedlings was compared to the sensitivity of mycorrhizal seedlings colonized either by a Cu-sensitive or Cu-tolerant S. luteus isolate. In nonmycorrhizal plants and plants colonized by the Cu-sensitive isolate, root growth and nutrient uptake were strongly inhibited under Cu stress conditions. In contrast, plants colonized by the Cu-tolerant isolate were hardly affected. The Cu-adapted S. luteus isolate provided excellent insurance against Cu toxicity in pine seedlings exposed to elevated Cu levels. Such a metal-adapted Suillus-Pinus combination might be suitable for large-scale land reclamation at phytotoxic metalliferous and industrial sites.     

Usefulness of HPV testing in the follow-up of untreated cervical low grade lesions

The aim of the present work was to evaluate the usefulness of high-risk human papillomavirus (HR-HPV) testing for the follow-up of women with untreated low grade cervical squamous cell lesions (LSIL). For that, 412 women with a cytological diagnosis of LSIL at entry were monitored by cytology, HR-HPV testing with the Hybrid Capture II assay (HC-II) and colposcopy. Our primary endpoint was clinical progression defined by the presence of a high grade cervical intraepithelial neoplasia (CIN2 and CIN3) at the biopsy. At baseline, histological control revealed 10 CIN2 and 11 CIN3 only in the cohort of women HR-HPV+. In the follow-up, 4 CIN2 and 8 CIN3 were detected, always in the women initially HR-HPV+. Thus, the recurrence of a HR-HPV+ infection clearly selects a population at high-risk for CIN2-3. The semi-quantitative appreciation of the viral load with HC-II could not be used as a good prognostic factor for the follow-up of women with LSIL. HR-HPV testing reduces the number of cytology and colposcopy examinations in the follow-up of women aged >35 years when HPV testing is initially negative. Thus HR-HPV testing should be reserved for the follow-up of this population of women initially HR-HPV+ and proposed 6 to 12 months after the cytological diagnosis of LSIL.