Conductance heterogeneities induced by multistability in the dynamics of coupled cardiac gap junctions.

In this paper, we study the propagation of the cardiac action potential in a one-dimensional fiber, where cells are electrically coupled through gap junctions (GJs). We consider gap junctional gate dynamics that depend on the intercellular potential. We find that different GJs in the tissue can end up in two different states: a low conducting state and a high conducting state. We first present evidence of the dynamical multistability that occurs by setting specific parameters of the GJ dynamics. Subsequently, we explain how the multistability is a direct consequence of the GJ stability problem by reducing the dynamical system's dimensions. The conductance dispersion usually occurs on a large time scale, i.e., thousands of heartbeats. The full cardiac model simulations are computationally demanding, and we derive a simplified model that allows for a reduction in the computational cost of four orders of magnitude. This simplified model reproduces nearly quantitatively the results provided by the original full model. We explain the discrepancies between the two models due to the simplified model's lack of spatial correlations. This simplified model provides a valuable tool to explore cardiac dynamics over very long time scales. That is highly relevant in studying diseases that develop on a large time scale compared to the basic heartbeat. As in the brain, plasticity and tissue remodeling are crucial parameters in determining the action potential wave propagation's stability.

Zonal expression of dickkopf-3 and components of the Wnt signalling pathways in the human adrenal cortex.

The mechanisms underlying the differentiation of the adrenal cortex into zones are unclear. Microarray studies on RNA from microdissected zona reticularis (ZR) and zona fasciculata/zona glomerulosa (ZF/ZG) derived from adult human adrenal glands showed that a gene of the dickkopf family (DKK), DKK3, is differentially expressed in the zones. The Dickkopf proteins are morphogens involved in Wnt signalling. Northern blotting showed higher DKK3 transcript levels in ZF/ZG than ZR samples. In situ hybridization on adult human adrenal gland sections showed that DKK3 expression was much higher in the ZG than in the ZF or ZR. DKK3 expression was also higher in the medulla. We screened for expression of other members of the DKK family and the related Wingless-type mouse mammary tumor virus integration site gene family (WNT), frizzled (FZD), and dishevelled (DVL) gene families. Among dickkopf family members, only DKK3 was expressed at a detectable level in both human and mouse adrenocortical RNA samples. Consistent with previously published data on the effects of Wnt4 gene disruption in the mouse, we found only WNT4 expression within the WNT family in both human and mouse RNA. Northern blotting showed that WNT4 was expressed at a higher level in ZF/ZG cells than in ZR. The higher level of DKK3 and WNT4 expression in ZF/ZG cells was confirmed by real-time PCR. In the frizzled and dishevelled families we found FZD1, FZD2 and DVL3 transcripts in human adrenocortical RNA, and FZD2 and DVL3 in mouse adrenocortical RNA. These data show that a variety of genes of the Wnt signalling pathways are expressed in the adrenal cortex. The zonal distribution of DKK3 expression suggests that it could be involved in zonal differentiation or growth.

Direct mass spectrometric analysis of in situ thermally hydrolyzed and methylated lipids from whole bacterial cells.

Fatty acid methyl esters (FAMEs) were generated in situ, during pyrolysis, from whole-cell bacterial samples and analyzed by mass spectrometry (MS). The FAME profiles obtained by an in situ thermal hydrolysis methylation (THM) step were compared with gas chromatography (GC) and MS analyses of the chemically extracted and methylated fatty acids. This correlation was based on the ability of each technique to differentiate a representative group of 15 bacteria at the species level as predicted by principal component analysis. All three analyses, GC/FAME, pyrolysis-MS/FAME, and in situ THM-MS/FAME differentiated the studied bacterial sample set into three discrete clusters. The bacteria comprising each cluster were the same for all three analyses, showing that taxonomic information of the lipid profiles was preserved in the Py-MS/FAME and in situ THM-MS/FAME analyses of whole cells. Contributions from saturated, unsaturated, cyclopropyl, and branched bacterial fatty acids to the differentiation of microorganisms were identified for all three analyses. The in situ THM-MS/FAME approach is simple, requires small samples (approximately 2 x 10(6) cells/profile), and is rapid, with a total analysis time under 5 min/sample.

In situ methylation of nucleic acids using pyrolysis/mass spectrometry.

Curie-point pyrolysis/triple quadrupole mass spectrometry (Py/MS/MS) has been used with tetramethylammonium hydroxide (TMAH) to conduct in situ methylation of nucleic acid bases. Nitrogen bases in free nucleotides, oligonucleotides, calf thymus DNA and whole bacterial cells reacted in situ during pyrolysis with TMAH to form the methylated bases. Derivatization increased the volatility of the nitrogen bases and the mass of the diagnostic base peaks, thereby removing them from the positions of lower-mass background peaks. The degree of methylation as a function of TMAH concentration for the oligonucleotide, calf thymus DNA, and the whole bacteria samples was determined and found to correlate with the nature of DNA. The methylated bases were identified by their positive-ion electron ionization fragmentation patterns and confirmed with tandem mass spectrometry. The detection of the methylated bases by Py/MS/MS facilitates the goal of identifying the nucleic acids in a complex mixture (i.e. whole bacterial cells) without extraction and prior derivatization.

Concurrent HPV-16 infection of the nipple and perianal area in an HIV-1+ patient. Military Medical Consortium for the Advancement of Retroviral Research (MMCARR)

BACKGROUND: In patients with HIV-1 disease there has been an increasing association with human papilloma virus (HPV) infections in multiple locations as well as an increase in associated tumors. In addition, there has been increased recovery of HPV in individuals with decreasing T4 cell counts. CASE REPORT: Recently we have seen an HIV-1+ patient with a cutaneous lesion on the nipple, as well as multiple perianal lesions in which HPV-16 was demonstrated by in-situ hybridization. Although these lesions contained the same subtype of HPV virus, they had very different clinical and histopathologic morphologies, and this represents the first reported association of HPV-16 in a nipple lesion. DISCUSSION: Our patient illustrates that in HIV-1 disease, HPV infections may present in more diffuse and atypical locations. In addition, the diffuse staining with the in-situ probe for HIV-16 within the lesions, tends to support the findings of others, that viral recovery increases with the immune suppression induced by HIV-1.