The role of stochastic and modal gating of cardiac L-type Ca2+ channels on early after-depolarizations

Certain signaling events that promote L-type Ca2+ channel (LCC) phosphorylation, such as beta-adrenergic stimulation or an increased expression of Ca(2+)/calmodulin-dependent protein kinase II, promote mode 2 gating of LCCs. Experimental data suggest the hypothesis that these events increase the likelihood of early after-depolarizations (EADs). We test this hypothesis using an ionic model of the canine ventricular myocyte incorporating stochastic gating of LCCs and ryanodine-sensitive calcium release channels. The model is extended to describe myocyte responses to the beta-adrenergic agonist isoproterenol. Results demonstrate that in the presence of isoproterenol the random opening of a small number of LCCs gating in mode 2 during the plateau phase of the action potential (AP) can trigger EADs. EADs occur randomly, where the likelihood of these events increases as a function of the fraction of LCCs gating in mode 2. Fluctuations of the L-type Ca2+ current during the AP plateau lead to variability in AP duration. Consequently, prolonged APs are occasionally observed and exhibit an increased likelihood of EAD formation. These results suggest a novel stochastic mechanism, whereby phosphorylation-induced changes in LCC gating properties contribute to EAD generation.     

Mycobacterium marinum Causes a Latent Infection that Can Be Reactivated by Gamma Irradiation in Adult Zebrafish

The mechanisms leading to latency and reactivation of human tuberculosis are still unclear, mainly due to the lack of standardized animal models for latent mycobacterial infection. In this longitudinal study of the progression of a mycobacterial disease in adult zebrafish, we show that an experimental intraperitoneal infection with a low dose (∼35 bacteria) of Mycobacterium marinum, results in the development of a latent disease in most individuals. The infection is characterized by limited mortality (25%), stable bacterial loads 4 weeks following infection and constant numbers of highly organized granulomas in few target organs. The majority of bacteria are dormant during a latent mycobacterial infection in zebrafish, and can be activated by resuscitation promoting factor ex vivo. In 5–10% of tuberculosis cases in humans, the disease is reactivated usually as a consequence of immune suppression. In our model, we are able to show that reactivation can be efficiently induced in infected zebrafish by γ-irradiation that transiently depletes granulo/monocyte and lymphocyte pools, as determined by flow cytometry. This immunosuppression causes reactivation of the dormant mycobacterial population and a rapid outgrowth of bacteria, leading to 88% mortality in four weeks. In this study, the adult zebrafish presents itself as a unique non-mammalian vertebrate model for studying the development of latency, regulation of mycobacterial dormancy, as well as reactivation of latent or subclinical tuberculosis. The possibilities for screening for host and pathogen factors affecting the disease progression, and identifying novel therapeutic agents and vaccine targets make this established model especially attractive.     

Indirect Immunofluorescence Assay for the Simultaneous Detection of Antibodies against Clinically Important Old and New World Hantaviruses

In order to detect serum antibodies against clinically important Old and New World hantaviruses simultaneously, multiparametric indirect immunofluorescence assays (IFAs) based on biochip mosaics were developed. Each of the mosaic substrates consisted of cells infected with one of the virus types Hantaan (HTNV), Puumala (PUUV), Seoul (SEOV), Saaremaa (SAAV), Dobrava (DOBV), Sin Nombre (SNV) or Andes (ANDV). For assay evaluation, serum IgG and IgM antibodies were analyzed using 184 laboratory-confirmed hantavirus-positive sera collected at six diagnostic centers from patients actively or previously infected with the following hantavirus serotypes: PUUV (Finland, n = 97); SEOV (China, n = 5); DOBV (Romania, n = 7); SNV (Canada, n = 23); ANDV (Argentina and Chile, n = 52). The control panel comprised 89 sera from healthy blood donors. According to the reference tests, all 184 patient samples were seropositive for hantavirus-specific IgG (n = 177; 96%) and/or IgM (n = 131; 72%), while all control samples were tested negative. In the multiparametric IFA applied in this study, 183 (99%) of the patient sera were IgG and 131 (71%) IgM positive (accordance with the reference tests: IgG, 96%; IgM, 93%). Overall IFA sensitivity for combined IgG and IgM analysis amounted to 100% for all serotypes, except for SNV (96%). Of the 89 control sera, 2 (2%) showed IgG reactivity against the HTNV substrate, but not against any other hantavirus. Due to the high cross-reactivity of hantaviral nucleocapsid proteins, endpoint titrations were conducted, allowing serotype determination in >90% of PUUV- and ANDV-infected patients. Thus, multiparametric IFA enables highly sensitive and specific serological diagnosis of hantavirus infections and can be used to differentiate PUUV and ANDV infection from infections with Murinae-borne hantaviruses (e.g. DOBV and SEOV).     

Increased Visceral Adipose Tissue as a Potential Risk Factor in Patients with Embolic Stroke of Undetermined Source (ESUS)

Purpose

The etiology of an ischemic stroke remains undetermined in 20–35% of cases and many patients do not have any of the conventional risk factors. Increased visceral adipose tissue (VAT) is a suggested new risk factor for both carotid artery atherosclerosis (CAA) and atrial fibrillation (AF), but its role in the remaining stroke population is unknown. We assessed the amount of VAT in patients with embolic stroke of undetermined source (ESUS) after excluding major-risk cardioembolic sources, occlusive atherosclerosis, and lacunar stroke.

Methods

Altogether 58 patients (mean age 57.7±10.2 years, 44 men) with ischemic stroke of unknown etiology but without CAA, known AF or small vessel disease underwent computed tomography angiography and assessment of VAT. For comparison VAT values from three different reference populations were used. Conventional risk factors (smoking, hypertension, diabetes, increased total and LDL-cholesterol, decreased HDL-cholesterol) were also registered.

Results

Mean VAT area was significantly higher in stroke patients (205±103 cm² for men and 168±99 cm² for women) compared to all reference populations (P<0.01). 50% of male and 57% of female patients had an increased VAT area. In male patients, VAT was significantly higher despite similar body mass index (BMI). Increased VAT was more common than any of the conventional risk factors.

Conclusion

Increased VAT was found in over half of our patients with ESUS suggesting it may have a role in the pathogenesis of thromboembolism in this selected group of patients.     

FLUCTUATING ASYMMETRY IN CENTRAL AND MARGINAL POPULATIONS OF LYCHNIS VISCARIA IN RELATION TO GENETIC AND ENVIRONMENTAL FACTORS

Developmental instability in the form of increased fluctuating asymmetry can be caused by either genetic or environmental stress. Because extinctions can be attributed broadly to these factors, fluctuating asymmetry may provide a sensitive tool for detecting such stresses. We studied the level of fluctuating asymmetry of flowers of a perennial outcrossing plant species, Lychnis viscaria, both in natural and common-garden populations. The degree of flower asymmetry was higher in small, isolated, and marginal populations of the species range. These marginal populations also were the most homozygous. In the core area of the species' range, flowers were more symmetrical The level of asymmetry was correlated with both population size and heterozygosity. However, a partial correlation analysis revealed that when the impact of population size was controlled for, there was a negative relationship between fluctuating asymmetry and heterozygosity, whereas when controlling for heterozygosity, no relationship between population size and fluctuating asymmetry was found. This indicates that genetic consequences of small population size probably underlie the relationship between the level of asymmetry and population size. Results from a transplantation experiment showed that individuals subjected to a higher environmental stress had an increased level of asymmetry compared to control plants. In the common-garden conditions the level of fluctuating asymmetry did not differ between the central and marginal populations. This suggests that presumably both genetic and environmental factors affected to the higher level of asymmetry among marginal populations compared to central ones. In all we conclude that even though fluctuating asymmetry seems to be a sensitive tool for detecting stresses, results from studies focusing on only one factor should be interpreted with caution.     

Genomic structure of the human ezrin gene

The ERM proteins, ezrin, radixin, and moesin, act as linkers between the plasma membrane and actin cytoskeleton. They are involved in a variety of cellular functions, such as cell adhesion, migration, and the organization of cell surface structures, and are highly homologous, both in protein sequence and in functional activity, with merlin/schwannomin, a neurofibromatosis-2-associated tumor-suppressor protein. We report here the genomic structure and intron junction sequences of the human ezrin gene. Ezrin consists of 13 exons and spans approximately 24 kb genomic DNA. The coding parts of the exons range in size from 12 bp to 275 bp and the introns from 182 bp to 7 kb. The genomic structures of ezrin and moesin are highly conserved, suggesting their recent divergence. Radiation hybrid mapping has refined the location of ezrin to the interval between D6S442 and D6S281. Received: 1 June 1998 / Accepted: 25 August 1998     

An approach to mapping haplotype-specific recombination sites in human MHC class III

Studies of the major histocompatibility complex (MHC) in mouse indicate that the recombination sites are not randomly distributed and their occurrence is haplotype-dependent. No data concerning haplotype-specific recombination sites in human are available due to the low number of informative families. To investigate haplotype-specific recombination sites in human MHC, we here describe an approach based on identification of recombinant haplotypes derived from one conserved haplotype at the population level. The recombination sites were mapped by comparing polymorphic markers between the recombinant and assumed original haplotypes. We tested this approach on the extended haplotype HLA A3; B47; Bf ^* F; C4A ^* 1; C4B ^* Q0; DR7, which is most suitable for this analysis. First, it carries a number of rare markers, and second, the haplotype, albeit rare in the general population, is frequent in patients with 21-hydroxylase (21OH) defect. We observed recombinants derived from this haplotype in patients with 21OH defect. All these haplotypes had the centromeric part (from Bf to DR) identical to the original haplotype, but they differed in HLA A and B. We therefore assumed that they underwent recombinations in the segment that separates the Bf and HLA B genes. Polymorphic markers indicated that all break points mapped to two segments near the TNF locus. This approach makes possible the mapping of preferential recombination sites in different haplotypes.     

Acute Phase IL-10 Plasma Concentration Associates with the High Risk Sources of Cardiogenic Stroke

Background

Etiological assessment of stroke is essential for accurate treatment decisions and for secondary prevention of recurrence. There is evidence that interleukin-10 (IL-10) associates with ischemic stroke. The aim of this prospective study was to assess the levels of IL-10 in ischemic stroke with unknown or suspected cardiogenic etiology, and evaluate the correlation between IL-10 plasma concentration and the number of diagnosed high risk sources for cardioembolism.

Methods

A total of 141 patients (97 males; mean age 61±11 years) with acute ischemic stroke with unknown etiology or suspected cardiogenic etiology other than known atrial fibrillation (AF) underwent imaging investigations to assess high risk sources for cardioembolic stroke established by the European Association of Echocardiography (EAE). IL-10 was measured on admission to the hospital and on a three month follow-up visit.

Results

Acute phase IL-10 concentration was higher in patients with EAE high risk sources, and correlated with their number (p<0.01). In patients with no risk sources (n = 104), the mean IL-10 concentration was 2.7±3.1 ng/L (range 0.3–16.3 ng/L), with one risk source (n = 26) 3.7±5.5 ng/L (0.3–23.6 ng/L), with two risk sources (n = 10) 7.0±10.0 ng/L (1.29–34.8 ng/L) and with three risk sources (n = 1) 37.2 ng/L. IL-10 level was not significantly associated with cerebral infarct volume, presence of previous or recent myocardial infarction, carotid/vertebral artery atherosclerosis, paroxysmal AF registered on 24-hour ECG Holter monitoring or given intravenous thrombolytic treatment.

Conclusion

IL-10 plasma concentration correlates independently with the number of EAE cardioembolic risk sources in patients with acute stroke. IL-10 may have potential to improve differential diagnostics of stroke with unknown etiology.     

Characterization of CA XIII, a novel member of the carbonic anhydrase isozyme family

The carbonic anhydrase (CA) gene family has been reported to consist of at least 11 enzymatically active members and a few inactive homologous proteins. Recent analyses of human and mouse databases provided evidence that human and mouse genomes contain genes for still another novel CA isozyme hereby named CA XIII. In the present study, we modeled the structure of human CA XIII. This model revealed a globular molecule with high structural similarity to cytosolic isozymes, CA I, II, and III. Recombinant mouse CA XIII showed catalytic activity similar to those of mitochondrial CA V and cytosolic CA I, with k(cat)/K(m) of 4.3 x 10(7) m(-1) s(-1), and k(cat) of 8.3 x 10(4) s(-1). It is very susceptible to inhibition by sulfonamide and anionic inhibitors, with inhibition constants of 17 nm for acetazolamide, a clinically used sulfonamide, and of 0.25 microm, for cyanate, respectively. Using panels of cDNAs we evaluated human and mouse CA13 gene expression in a number of different tissues. In human tissues, positive signals were identified in the thymus, small intestine, spleen, prostate, ovary, colon, and testis. In mouse, positive tissues included the spleen, lung, kidney, heart, brain, skeletal muscle, and testis. We also investigated the cellular and subcellular localization of CA XIII in human and mouse tissues using an antibody raised against a polypeptide of 14 amino acids common for both human and mouse orthologues. Immunohistochemical staining showed a unique and widespread distribution pattern for CA XIII compared with the other cytosolic CA isozymes. In conclusion, the predicted amino acid sequence, structural model, distribution, and activity data suggest that CA XIII represents a novel enzyme, which may play important physiological roles in several organs.