The development of the atrioventricular canal (A-V canal) of embryonic chick hearts (35 to 120 h) was studied by morphological and electrophysiological techniques. The earliest identification of the ...A-V canal action potentials was at 45 to 49 h of incubation coinciding with the atrium formation and the appearance of its corresponding distinctive action potential. At that time the first atrioventricular delay was recorded and its action potentials showed a low rate of rise, particularly at the initiation of the upstroke and a long duration. The conduction velocity was the lowest in the A-V canal. As the development proceeded from 45 to 120 h, the cardiac cells of the A-V canal showed scanty membrane to membrane contacts and large intercellular spaces filled with abundant extracellular matrix components, in striking contrast to the paucity of these components in the atrium and ventricle. The morphological and electrophysiological characteristics described for the A-V canal cells, could help to explain their slow conduction properties and the atrioventricular delay.
Human leukocyte antigen (HLA) class I polymorphism was studied within a population of 70 unrelated Kolla Amerindians from the far northwest of Argentina close to the Bolivian border. The results ...indicate that the HLA-A, -B, and -C alleles typical of other Amerindian populations also predominate in the Kolla. These alleles belong to the following allele groups: HLA-A∗02, ∗68, ∗31, ∗24, HLA-B∗35, ∗15, ∗51, ∗39, ∗40, ∗48, and Cw∗01, ∗03, ∗04, ∗07, ∗08, and ∗15. For the HLA-A locus, heterogeneity was seen for HLA-A∗02 with A∗0201, ∗0211, and ∗0222; and for A∗68 with ∗68012 and ∗6817, the latter being a novel allele identified in this population. Analysis of HLA-B identified heterogeneity for all Amerindian allele groups except HLA-B∗48, including the identification of the novel B∗5113 allele. For HLA-C heterogeneity was identified within the Cw∗07, ∗04, and ∗08 groups with Cw∗0701/06, ∗0702, ∗04011, ∗0404, ∗0803, and ∗0809 identified. The most frequent “probable” haplotype found in this population was B∗3505-Cw∗04011. This study supports previous studies, which demonstrate increased diversity at HLA-B compared with HLA-A and -C. The polymorphism identified within the Kolla HLA-A, -B, and -C alleles supports the hypothesis that HLA evolution is subject to positive selection for diversity within the peptide binding site.
The effect of heparin (1–200μg/ml) on several functional properties of 4-day-old embryonic hearts was studied. Intracellular recordings either from cells of the atrium, the atrio–ventricular canal or ...the ventricle were made on the isolated and perfused hearts. In all impaled myocardial cells, heparin produced an increment in the maximal rate of rise and amplitude of the action potentials and the duration was slightly diminished. In addition, heparin provoked a reduction in the spontaneous beating frequency, while the electrical excitability and the conduction velocity of the atrium and the ventricle were increased. The measurements of atrio–ventricular latency revealed that it was diminished, i.e. the propagation of impulses through the atrio–ventricular canal was improved. Simultaneously with these changes, heparin incremented the amplitude of contraction of either the atrium or the ventricle importantly.
Isolated wheat (
Triticum aestivum var. Potam) aleurone layers have a high capacity to acidify their environment, and secrete hydrolytic enzymes (endoxylanase, glucanase, α-amylase, proteases, etc.) ...under the control of GA
3. Acidic pH and xylanases are found to be essential for cell wall relaxation in growing tissues, but aleurone is a non-growing, non-dividing tissue. In this tissue, we studied the effect of these loosening factors on aleurone cell walls.Exposure to pH 3.0 caused the release of carbohydrates and calcium ions from the pericarp, and a small amount of carbohydrates, mainly polysaccharides, from aleurone layers from which pericarp tissue had been removed. 50 percnt; of the total sugars released into the incubation medium by these isolated aleurone tissue was arabinose, but no xylose, calcium ions, or phenolic compounds were found. Acid preincubation decreased by 30 percnt; the susceptibility of aleurone cell walls to degradation by exogenously-applied endoxylanase, and also modified the architecture of cell wall as observed by autofluorescence of phenolic groups. These findings suggest that acid treatment and endoxylanase action, rather than having a loosening effect on aleurone cell wall, can have an opposite effect, increasing the resistance of aleurone cell walls to loosening.
During leishmania infection, parasites are inoculated to the human host through the bite of a sandfly vector into the dermis, where they first interact with tissue components, cells and extracellular ...matrix molecules. Since collagen is the most abundant component of the skin matrix, we investigated whether there is a specific interaction ofLeishmania mexicanapromastigotes with this host component. Promastigotes were able to attach to collagen fibrils and move through the matrix of mouse skin sections and to penetrate easily into a type I collagen gel. Denatured type I collagen coated beads (Cytodex 3) readily bound to the parasite surface. The interaction of promastigotes with type 1 collagen was dose dependent and saturable and was competitively and specifically inhibited with increasing concentrations of gelatin. Biotin-labeled parasite surface molecules were able to associate with both denatured collagen from microcarriers and native type I collagen from bovine kidney. It is suggested that the presence of parasite cell membrane receptors to collagen may confer a specific tropism for the skin, where collagen is the most abundant component of the matrix.
A detailed study of the structure and ultrastructure of Sparganum proliferum was made possible for the first time thanks to the successful in vitro and in vivo maintenance of this rare parasite. ...Although S. proliferum exhibits many of the classical tegumental and parenchymal structures previously described for other larval cestodes, these are either arranged in a distinct fashion or, in some cases, may be completely different. Among the latter and of special interest are the single or multiple parenchymal cavities, surrounded by tegument, which in some instances appear to act as a primitive digestive tract.
Human samples of articular cartilage from the knee of a clinically classified osteoarthritic patient, assessed by arthroscopy as part of the surgical treatment was studied by light and transmission ...electron microscopy. This particular case differed from others already reported in the variability of cell phenotype within the aggregates or "clones" frequently present in the osteoarthritic cartilage. The most common morphology of "clonal" cells forming the aggregates were large and rounded with an euchromatic nucleus. The cytoplasm was characterized by the presence of alternately clear and dense sites. At the ultrastructural level it was seen that the clear sites were formed by disrupted intermediates filaments and small particles, and that the dense sites were constituted by the segregation of different organelles of the chondrocytes. In addition, there were atypical aggregates composed only by secretory cells or by degenerating chondrocytes. Furthermore, a complex structure consisting of a very large cell inside a giant lacunae delimited by electron-dense material with small vesicles is described as a novel finding. The variability in the chondrocyte phenotype of the aggregates described here could be an indication of a better prognosis; nevertheless, the follow-up of the evolution of this patient is needed in order to know the final outcome.
A study of the encapsulation of poly(U) and poly(C) within liposomes made from dipalmitoylphosphatidyl choline (DPPC), from egg yolk phosphatidyl choline (PC), and from PC with cholesterol (CHOL) was ...made. The liposomes were prepared under anoxic conditions following the reverse-phase evaporation method. Determinations showed that 36 to 70% of the available lipids form liposomes and 2 to 5% of the polyribonucleotides can be entrapped by liposomes. The encapsulation of polyribonucleotides has also been measured in the presence of urea, cyanamide and Zn++, condensing agents in prebiotic polymerization reactions. DPPC and PC:CHOL liposomes were formed in the presence of 1.0 M urea, although no PC liposomes were formed. The three types of liposomes were readily formed at 0.01 M urea, but in no case an enhancement of encapsulation efficiency of poly(U) was observed due to the presence of urea. Similar results were obtained with cyanamide. An enhanced encapsulation of poly(U) by the three types of liposomes was observed when Zn++ was in the range of 0.001 to 0.01 M. Poly(U) encapsulation was 15 to 25 times higher when liposomes were prepared from DPPC at 0.01 M Zn++. Similar results were obtained with poly(C). The advantages of DPPC-polyribonucleotide liposomes as precellular systems are discussed.
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