Analysis of cytoskeleton structural changes in the granular cells of the frog bladder during the stimulation of water transport

Structural changes of the cytoskeleton of the frog urinary bladder granular cells were examined during low and high water permeability of the epithelium. A tight connection of the microfilaments and microtubules with vacuolar membranes and a great increase in the number of microtubules during a stimulated water flow was shown using different electron microscopic methods. Two populations of microtubules were discovered, respectively, with different diameter and different rate of stability. It is suggested that the thicker microtubules while interacting with actin microfilaments through associated electron dense globules may fulfil the transport function in the cell.     

Electron microscopic research on the mitochondria-rich bladder cells of the frog

The ultrastructural peculiarities of mitochondria-rich cells of the frog urinary bladder are analysed using three electron microscopic methods: ultrathin sections, scanning electron microscopy, freeze fracture. The mitochondria and tubular and vesicular structures are most abundant in the apical region of cytoplasm. The P-face (PF) of the apical plasma membrane is characterized by the presence of rod-shaped intramembrane particles (IMP), whereas the E-face (EF) possesses complementary pits. Depending on the distribution density of the rod-shaped IMP, three types of cells are described. The apical plasma membrane has an invert distribution of the globular IMP: a great quantity of IMP on the EF and a few particles on the PF. This structure of the apical plasma membrane is supposed to correlate with its very low water permeability. Using filipin as a marker of cholesterol localization, it has been shown that the mitochondria-rich cell apical membrane contains more cholesterol than that of the granular cells. The nature of the rod-shaped IMP and their role in the transmembrane ion transport have been discussed.     

The characteristics of the ultrastructural organization of the apical plasma membrane of epithelial cells secreting hydrogen ions

The analysis of ultrastructural characteristics of mitochondria-rich cells of the frog urinary bladder with the aid of three electron microscopic methods (ultrathin sections, scanning electron microscopy, freeze-fracture) has been done. The inverted distribution of globular intramembrane particles (IMP) in apical membranes reflecting their low water permeability has been shown. The typical feature of plasma membranes of mitochondria-rich cells is the presence of rod-shaped IMP on the P-face of the apical membrane and complementary pits on the EF. There is a correlation between the quantity of rod-shaped IMP and the rate of ionic transport. The analysis of cholesterol contents in plasma membranes of epithelial cells of the frog urinary bladder has shown that the apical membranes of mitochondria-rich cells contain more cholesterol than those of granular cells; the great pat of cholesterol is localized in the cytoplasmic leaflet.     

Ultrastructure of the specialized intercellular contacts in an L-cell culture treated with low concentrations of lanthanum]

The electron microscope study of L-cells treated with 1 mM lanthanum has shown an increased amount of gap-like junctions and a decreased number of tight junctions compared to the norm. No damage in the plasma membrane structure and other cell organoids was observed. This may suggest that following the above treatment, the amplified intercellular exchange is associated with the increase in the quantity of intercellular highly permeable junctions. In this case lanthanum may serve as a membrane structure modificator. This effect must be taken into account when the electron microscopists use the lanthanum label for studying specialized intercellular junctions.     

Aquaporins of plasma membranes of epithelial cells

The early 90s have brought us a discovery of a new class of membrane proteins--aquaporins with a function of transmembrane water channels. Being genetically closed proteins aquaporins are members of a large family of channel-forming proteins called MIPs (major intrinsic proteins). All aquaporins, except AQP4, are mercury-sensitive. Many aquaporins have been cloned and identified. Polyclonal antibodies grown against some of them promoted numerous studies of aquaporin localization and distribution in animal and plant tissues. Up to the present, 10 and 2 aquaporins have been described in mammalian and amphibian epithelial tissues, respectively. One of described aquaporins, AQP2, whose localization is confined to kidney collecting duct principal cells, has been found to be a hormone-depending water channel. The insertion of apical vesicles bearing AQP2 was shown to be regulated by vasopressin, meanwhile all other aquaporins are inserted into the plasma membrane constitutively. There is a vast evidence showing that the integrity of microtubules is necessary for both pathways of aquaporin insertion. AQP2 is important for normal kidney functioning and AQP2 mutations cause water-balance disorders. On the contrary, the AQP1 mutations are not accompanied by any evident clinical pathology. This review is focused on a discussion of the data so far available on aquaporin distribution in different animal tissues.     

Immunocytochemical localization of vasopressin at its absorption by cells of rat small intestine

Morpho-physiological characteristics of the transport of cyclic nonapeptide arginine vasopressin (AVP) across the rat intestinal epithelium was studied in experiments in vitro. A partial absorption of physiologically active AVP was followed when filling the isolated intestinal lumen by hormone solution. By methods of immunoelectron and immunofluorescence confocal microscopy, using polyclonal anti-AVP antibodies, cytoplasmic localization of AVP label was shown in enterocytes. The AVP label was also observed in the intercellular space in the basal area of epithelium. No label was revealed in the intercellular junctions, and no predominant label accumulation was found in any cytoplasmic structures of the epithelial cells. The obtained results are considered as evidence for the transcellular pathway of partial AVP absorption in rat small intestine.     

Structural and functional analysis of glucose adsorption at high maltose concentrations in the rat small intestine in vivo

To elucidate the mechanism of glucose absorption at high substrate concentrations, we studied structural and ultrastructural peculiarities of enterocytes arranged at different levels along the intestinal villus. The preparations were obtained from an isolated segment of the rat small intestine after its perfusion with maltose solutions with both low (25 mM) and high (100 mM) concentrations, respectively. Under conditions of chronic experiment at high substrate concentration, an enlargement of intercellular clefts, indicating glucose absorption, occurred in deeper areas of the villus. Besides, also in chronic experiment, we studied kinetics of maltose hydrolysis and derived glucose absorption in the isolated segment of the rat small intestine after its perfusion with maltose at superhigh (up to 200 mM) initial concentrations. Based on these data, a conclusion is made that active transport is the main mechanism of absorption of glucose derived from maltose hydrolysis, operating both at low disaccharide concentrations, and in the range of its superhigh (up to 200 mM) concentrations.     

Variants in the interleukin-1 alpha and beta genes,and the risk for periodontal disease in dogs

Elevated levels of interleukin-1 (IL-1) have been shown to amplify the inflammatory response against periodontopathogenic bacteria. In humans, polymorphisms in the IL1A and IL1B genes are the most well-studied genetic polymorphisms associated with periodontal disease (PD). In contrast to human, there is a lack of knowledge on the genetic basis of canine PD. A case–control study was conducted in which a molecular analysis of dog IL1A and IL1B genes was performed. Of the eight genetic variants identified, seven in IL1A gene and one in IL1B gene, IL1A/1_g.388A >C and IL1A/1_g.521T >A showed statistically significant differences between groups (adjusted OR (95% CI): 0.15 (0.03–0.76), P= 0.022; 5.76 (1.03–32.1), P= 0.046, respectively). It suggests that in the studied population the IL1A/1_g.388C allele is associated with a decreased PD risk, whereas the IL1A/1_g.521A allele can confer an increased risk. Additionally, the IL1A/2_g.515G >T variation resulted in a change of amino acid, i.e. glycine to valine. In silico analysis suggests that this change can alter protein structure and function, predicting it to be deleterious or damaging. This work suggests that IL1 genetic variants may be important in PD susceptibility in canines.     

Structural-functional organization of Golgi apparatus

This review is dedicated to the structure and function of Golgi apparatus (GA). It summarizes contemporary data published in numerous experimental papers and in several reviews. Possible ways of intra-Golgi transport of proteins, existent models of structural and functional organization of Golgi organelle, as well as the issues of its biogenesis, posttranslational modification and sorting of proteins and lipids, and mechanisms of their traffic-king are discussed. Special attention is paid to the role of coatomer proteins (COPI, COPII and clathrin), fusion proteins (SNAREs), and small GTPases (ARF, SARI) in the secretory pathway. In addition, the phenomena of ultrastructural alterations of GA due to various functional conditions and physiological stimuli are specifically accented. We included in this review our original data on a probable involvement of GA in water transport, and on the organization of atypical GA in microsporidia--intracellular parasitic protists.