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At least 1,171 records · Page 65Linked to original sources
PubMed1996

The influence of merocyanine 540 and protoporphyrin on physicochemical properties of the erythrocyte membrane.

The interaction of the red cell membrane with merocyanine 540 or protoporphyrin led to four phenomena, most probably interrelated. (i) The morphology changed from the normal discoid to an echinocytic form. This morphological change persisted when followed over a period of 24 h. (ii) Simultaneously, cell deformability was decreased, as revealed by viscosity measurements and a cell-filtration technique. (iii) Both drugs caused swelling of the erythrocytes in isotonic medium, due to a very-short-term increased permeability of the membrane, also for larger molecules such as lactose. The pathway of this temporary leak seems to be unrelated to the Na+/K+ -ATPase, the K+/Cl- and the Na+/K+/Cl- cotransport systems, the Ca2+-activated Gardos pathway, the oxidation/deformation-activated leak pathway and the so-called residual transport route. Despite the morphological changes, K+-leakage induced by mechanical stress was not increased. (iv) During osmotic swelling, the critical hemolytic volume was found to be increased in the presence of either merocyanine 540 or protoporphyrin. The increase critical volume protected erythrocytes against osmotic hemolysis.

Antiviral Agents↗
PubMed1997

An electrophysiological method for measuring the potassium permeability of the nerve perineurium.

An electrophysiological method is described for measuring the potassium permeability (PK) of the perineurium of the sciatic nerve of the frog. The method is based on the principle of grease-gap recording, in which an insulating compartment separates two surface recording electrodes. The sciatic nerves of frogs Rana temporaria and R. pipiens were isolated and mounted across a five compartment chamber, with Vaseline grease seals on the partitions between compartments. Compartments #1, #2 and #5 contained frog Ringer solution, #4 was filled with Vaseline and formed the grease gap, and #3 was the test compartment in which solutions could be changed. The nerve was stimulated via platinum electrodes in compartments #1 and #2, and DC potentials and compound action potentials (CAP) were recorded between Ag/AgCl electrodes connected through Ringer-agar bridges to compartments #3 and #5. In nerves with undamaged perineurium, changing from normal Ringer to high [K+] Ringer (100 mM, KCl replacing NaCl) for 2 min caused negligible change in DC potential or CAP, indicating that raised [K+] was not reaching the axon surface, and hence that the perineurium was exerting a diffusional restriction on K+ entry. In nerves damaged by stretching or drying, K+ pulses caused a depolarising change in DC potential (delta DC), and corresponding decline in CAP amplitude, consistent with a leaky perineurium allowing K+ entry and axonal depolarisation. Ringer made hypertonic by the addition of 2.5 M sucrose or 5 M NaCl caused increased perineurial permeability to K+. The method was calibrated by measuring the delta DC in response to raised [K+] in the range 5-100 mM [K+] in desheathed nerves; from this calibration curve relating delta DC to endoneurial [K+] it was possible to calculate the change in endoneurial [K+] occurring in intact preparations. The calculations showed that the undamaged perineurium had a PK of < 6.3 x 10(-7) cm.s-1, similar to the value calculated for in situ nerves using radioisotopic techniques, but less than the value reported for isolated perineurial cylinders. The method gives real-time information on the K+ permeability of the nerve perineurium and its modulation by experimental treatments.

Animals↗
PubMed1999

Pore charge distribution considerations in human epidermal membrane electroosmosis.

The aim of this study was to assess the extent to which a model with pores having only net negative charges would adequately describe transdermal electroosmosis in human epidermal membrane (HEM) at neutral pH. Such information would enhance the predictive value of the modified Nernst-Planck model for transdermal iontophoresis, in addition to providing insights regarding the likelihood of significant pore charge distribution in HEM. Baseline results (the control) obtained from 0.1 to 0.4 V anodal and cathodal electroosmosis experiments with synthetic polycarbonate membranes (Nuclepore membranes), using radiolabeled urea and mannitol as the model permeants, demonstrated that such a membrane system can be modeled by the electrokinetic (electroosmosis) theory with the assumption of the pores possessing only negative charges. The studies with HEM were carried out at low voltage (</=0.5 V) where alterations in the barrier properties of HEM were minimal and at higher voltages (>/approximately = 1.0 V) where significant field-induced pore formation in HEM occurred. In both the low and high voltage studies, radiolabeled urea, mannitol, and water were employed as permeants in cathodal and anodal iontophoresis experiments. The results of the low voltage iontophoresis experiments suggest significant pore charge distribution in HEM (a significant deviation between the predictions from the single pore charge type assumption and the experimental data). Under the higher applied voltage conditions (>/approximately = 1.0 V), results from anodal and cathodal electroosmosis studies were consistent with the model in which the HEM has only pores that are net negatively charged.

Algorithms↗
PubMed1998

Highly water-permeable type I alveolar epithelial cells confer high water permeability between the airspace and vasculature in rat lung.

Water permeability measured between the airspace and vasculature in intact sheep and mouse lungs is high. More than 95% of the internal surface area of the lung is lined by alveolar epithelial type I cells. The purpose of this study was to test whether osmotic water permeability (Pf) in type I alveolar epithelial cells is high enough to account for the high Pf of the intact lung. Pf measured between the airspace and vasculature in the perfused fluid-filled rat lung by the pleural surface fluorescence method was high (0.019 +/- 0.004 cm/s at 12 degrees C) and weakly temperature-dependent (activation energy 3.7 kcal/mol). To resolve the contributions of type I and type II alveolar epithelial cells to lung water permeability, Pf was measured by stopped-flow light scattering in suspensions of purified type I or type II cells obtained by immunoaffinity procedures. In response to a sudden change in external solution osmolality from 300 to 600 mOsm, the volume of type I cells decreased rapidly with a half-time (t1/2) of 60-80 ms at 10 degrees C, giving a plasma membrane Pf of 0.06-0.08 cm/s. Pf in type I cells was independent of osmotic gradient size and was weakly temperature-dependent (activation energy 3.4 kcal/mol). In contrast, t1/2 for type II cells in suspension was much slower, approximately 1 s; Pf for type II cells was 0.013 cm/s. Vesicles derived from type I cells also had a very high Pf of 0.06-0.08 cm/s at 10 degrees C that was inhibited 95% by HgCl2. The Pf in type I cells is the highest measured for any mammalian cell membrane and would account for the high water permeability of the lung.

Animals↗
PubMed1996

Expression and functional analysis of water channels in a stably AQP2-transfected human collecting duct cell line.

In this study, we describe the establishment of a stably transfected epithelial cell line with the cDNA for the rat aquaporin 2 (AQP2). To this end, we used a human cell line (HCD) derived from the cortical collecting duct and having characteristics of principal cells (Prié, D., Friedlander, G., Coureau, C., Vandewalle, A., Cassigena, R., and Ronco, P. M. (1995) Kidney Int. 47, 1310-1318). The HCD cells were first screened for the constitutive expression of AQPs. By Western blot analysis, we found a low expression of immunoreactive AQP2 and AQP4 proteins. In contrast, transfected cells (clone CD8) probed with AQP2 antiserum expressed an intense 29-kDa protein on immunoblot in addition to a broad band between 35-45 kDa corresponding to the glycosylated form of the protein, indicating that full maturity of the protein is attained in transfected cells. Immunofluorescence demonstrated that AQP2 was located in intracellular vesicles. After vasopressin stimulation, the staining redistributed from an intracellular site to the apical pole of the cells, an effect similar to that described on collecting duct principal cells in vivo (Sabolic, I., Katsura, T., Verbavatz, J. M., and Brown, D. (1995) J. Membr. Biol. 143, 165-175) and in perfused tubules (Nielsen, S., Chou, C. L., Marples, D., Christensen, E. I., Kishore, B. K., and Knepper, M. A. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 1013-1017). The redistribution of AQP2 in CD8 cells was accompanied by an approximately 6-fold increase in osmotic water permeability coefficient (Pf), which was inhibited by 0.3 m HgCl2. These data indicate that functional vasopressin-sensitive water channels are expressed in transfected cells. The stably transfected cells represent a suitable model to unravel by direct experimental approach the intracellular signals involved in the translocation of AQP2 to the apical plasma membrane in the presence of vasopressin.

Amino Acid Sequence↗
PubMed2006

Transient osmotic absorption of fluid in microvessels exposed to low concentrations of dimethyl sulfoxide.

Dimethyl Sulfoxide (DMSO) is a common solvent for pharmacological agents. It is a small, lipophilic molecule thought to be relatively highly permeable through the cell membrane. While measuring the effect of low concentrations of DMSO (0.05-0.5% v/v) on capillary hydraulic conductivity as a vehicle control for pharmacological agents, the authors noticed what appeared to be an unusual transient absorption of fluid across the vessel wall. This absorption occurred during occlusion of the vessel, but dissipated quickly (1.7-8.6 s). The transient reabsorption reappeared upon each successive occlusion. To determine the nature of this transient absorption, the authors have measured the effect of increasing the pressure of the perfusing solution, of the concentration and time of perfusion of DMSO, and of superfusing the DMSO. They found that the absorption rate, but not the filtration rate, was concentration dependent, and was significantly correlated with the osmotic pressure of the DMSO. Moreover, the time taken for completion of the transient, i.e., time to reversal of flow, was inversely proportional to the hydraulic conductivity of the vessel. Furthermore, the transient absorption could be reduced and eventually abolished by increasing the hydrostatic pressure. These results strongly suggested that perfusion with low concentrations of DMSO could set up a significant osmotic pressure gradient across the vessel wall. This proposed mechanism for the absorption was confirmed by the measurement of a significant osmotic reflection coefficient of the vessel wall to DMSO (0.11 +/- 0.01). Relatively low concentrations (0.05-0.5%) of DMSO were therefore able to stimulate a significant osmotic transient across the blood vessel walls.

Absorption↗
PubMed1970

Ionic peremability of thin lipid membranes. Effects of n-alkyl alcohols, polyvalent cations, and a secondary amine.

Ultrathin (black) lipid membranes were made from sheep red cell lipids dissolved in n-decane. The presence of aliphatic alcohols in the aqueous solutions bathing these membranes produced reversible changes in the ionic permeability, but not the osomotic permeability. Heptanol (8 mM), for example, caused the membrane resistance (R(m)) to decrease from >10(8) to about 10(5) ohm-cm(2) and caused a marked increase in the permeability to cations, especially potassium. In terms of ionic transference numbers, deduced from measurements of the membrane potential at zero current, T(cat)/T(Cl) increased from about 6 to 21 and T(K)/T(Na) increased from about 3 to 21. The addition of long-chain (C(8)ndash;C(10)) alcohols to the lipid solutions from which membranes were made produced similar effects on the ionic permeability. A plot of log R(m) vs. log alcohol concentration was linear over the range of maximum change in R(m), and the slope was -3 to -5 for C(2) through C(7) alcohols, suggesting that a complex of several alcohol molecules is responsible for the increase in ionic permeability. Membrane permselectivity changed from cationic to anionic when thorium or ferric iron (10(-4)M) was present in the aqueous phase or when a secondary amine (Amberlite LA-2) was added to the lipid solutions from which membranes were made. When membranes containing the secondary amine were exposed to heptanol, R(m) became very low (10(3)-10(4) ohm-cm(2)) and the membranes became perfectly anion-selective, developing chloride diffusion potentials up to 150 mv.

Alcohols↗
PubMed1964

STABILIZATION OF STREPTOCOCCUS FAECALIS PROTOPLASTS BY SPERMINE.

Harold, F. M. (National Jewish Hospital, Denver, Colo.). Stabilization of Streptococcus faecalis protoplasts by spermine. J. Bacteriol. 88:1416-1420. 1964.-Lysis of protoplasts of Streptococcus faecalis subjected to osmotic shock was prevented by the presence of 10(-3)m spermine and other divalent cations. Protein and nucleic acids were largely retained, but compounds of low molecular weight were discharged into the medium and the capacity for glycolysis was lost. Under these conditions, spermine was bound to the protoplasts. It could not be removed by washing with water or nonelectrolytes, but was displaced by salts, polyanions, and polycations. Removal of the spermine restored the osmotic fragility of the protoplasts, which could once again be protected from lysis by impermeant solutes. Protoplasts were also stabilized, in the absence of osmotic shock, by prolonged incubation with cations in 0.5 m sucrose. By either procedure, the protoplasts became resistant not only to osmotic lysis but also to sonic oscillation. It is concluded that the stabilization of protoplasts resulted from ionic binding of the cation to acidic sites on the external surface of the plasma membrane. This conferred upon the membrane additional mechanical strength, perhaps by the cross-linking of subunits, but did not alter its permeability to extracellular solutes.

Bacteriolysis↗
PubMed1976

Replicative bacteriophage DNA synthesis in plasmolyzed T4-infected cells: evidence for two independent pathways to DNA.

Bacteriophage T4-infected Escherichia coli rendered permeable to nucleotides by sucrose plasmolysis exhibited two apparently separate pathways or channels to T4 DNA with respect to the utilization of exogenously supplied substrates. By one pathway, individual labeled ribonucleotides, thymidine (tdR), and 5-hydroxymethyl-dCMP could be incorporated into phage DNA. Incorporation of each of these labeled compounds was not dependent upon the addition of the other deoxyribonucleotide precursors, suggesting that a functioning de novo pathway to deoxyribonucleotides was being monitored. The second pathway or reaction required all four deoxyribonucleoside triphosphates or the deoxyribonucleoside monophosphates together with ATP. However, in this reaction, dTTP was not replaced by TdR. The two pathways were also distinguished on the basis of their apparent Mg2+ requirements and responses to N-ethylmaleimide, micrococcal nuclease, and to hydroxyurea, which is a specific inhibitor of ribonucleoside diphosphate reductase. Separate products were synthesized by the two channels, as shown by density-gradient experiments and velocity sedimentation analysis. Each of the pathways required the products of the T4 DNA synthesis genes. Furthermore, DNA synthesis by each pathway appeared to be coupled to the functioning of several of the phage-induced enzymes involved in deoxyribonucleotide biosynthesis. Both systems represent replicative phage DNA synthesis as determined by CsCl density-gradient analysis. Autoradiographic and other studies provided evidence that both pathways occur in the same cell. Further studies were carried out on the direct role of dCMP hydroxymethylase in T4 DNA replication. Temperature-shift experiments in plasmolyzed cells using a temperature-sensitive mutant furnished strong evidence that this gene product is necessary in DNA replication and is not functioning by allowing preinitiation of DNA before plasmolysis.

Adenosine Triphosphate↗
PubMed1975

Release of cyclic AMP by toad urinary bladder.

Cyclic AMP accumulates in the Ringer solution bathing the toad urinary bladder in vitro. At least 4 times more cyclic AMP is released into the solution bathing the serosal surface than into the solution bathing the mucosal surface. Most of the cyclic AMP originates in the epithelial cells rather than the stroma. Vasopressin increased the content of cyclic AMP in the epithelial cells and increases the amount of cyclic AMP in the Ringer solution. Since there is not an increase in medium cyclic AMP when cell cyclic AMP levels are increased by theophylline, it is suggested that theophylline may reduce the permeability of the cell membrane to cyclic AMP. Finally, it is demonstrated that 10 mM NaF increase the amount of cyclic AMP in the epithelial cells and in the solution bathing the bladder, but block the effect of vasopressin on water permeability, presumably at a step subsequent to the formation of cyclic AMP.

Animals↗