Diffusion Of Glycerol Research Articles

Hydration of the stratum corneum

Synopsis Topically applied water, occlusion and topically applied glycerol were used to investigate and characterize some of the changes which occur in the hydrated stratum corneum. The effects of these treatments were monitored using non-invasive techniques under controlled conditions. The Servomed Evaporimeter was used to determine natural water flux from the skin surface before and after treatment. The performance of the Evaporimeter in this type of study had previously been improved by attaching a paper baffle to the detector. This eliminated the variance in output caused by atmospheric movement. Experiments were carried out at temperatures below the threshold of thermal sweating and emotional sweating was minimized. Skin surface topography was characterized by means of a new type of profilometer. The instrument's design allowed a diamond stylus to traverse the living skin surface without significantly altering its structure. Changes in skin surface roughness were further elucidated using scanning electron microscopy and macrophotography. In vivo penetration of glycerol was assessed by chemical analysis of stratum corneum layers of treated skin. Samples were obtained by sequential stripping of the stratum corneum using adhesive tape. Topically applied water produced only a transient benefit because of rapid evaporation. More prolonged hydration was achieved by suppressing transepidermal water loss with polyethylene film. This occlusive hyperhydration was characterized by a significant reduction in profile roughness and by a smoother macroscopic appearance. Glycerol achieved the same effects by reducing the magnitude of the natural water flux from the skin surface and by reducing the rate of evaporation of water from applied aqueous glycerol solution or cosmetic product. Both effects were seen as the result of lowered water activity in the proximity of glycerol. Smoothing effects of glycerol on the skin surface, and improved appearance, persisted for at least 24 h. This persistence was explained by evidence for diffusion of glycerol into the stratum corneum where it formed a reservoir. Hydration of the skin is known to affect its barrier function and thereby exert a profound effect on penetration of both lipophilic and hydrophilic molecules. Clinically, this effect may be achieved using liberal applications of occlusive petroleum jelly and ointments. The results presented in this paper suggest that the use of humectants could achieve useful hydration using cosmetically acceptable materials.

Inhibition of sugar uptake by ascorbic acid in Escherichia coli

The uptake of glucose by the glucose phosphotransferase system in Escherichia coli was inhibited greater than 90% by ascorbate. The uptake of the nonmetabolizable analog of glucose, methyl-α-glucoside, was also inhibited to the same extent, confirming that it was the transport process that was sensitive to ascorbate. Similarly, it was the transport function of mannose phosphotransferase for which mannose and nonmetabolizable 2-deoxyglucose were substrates that was partially inhibited by ascorbate. Other phosphotransferase systems, including those for the uptake of sorbitol, fructose and N-acetylglucosamine, but not mannitol, were also inhibited to varying degrees by ascorbate. The inhibitory effect on the phosphotransferase systems was reversible, required the active oxidation of ascorbate, was sensitive to the presence of free-radical scavengers, and was insensitive to uncouplers. Because ascorbate was not taken up by E. coli, it was concluded that the active inhibitory species was the ascorbate free radical and that it was interacting reversibly with a membrane component, possibly the different enzyme IIB components of the phosphotransferase systems. Ascorbate also inhibited other transport systems causing a slight reduction in the passive diffusion of glycerol, a 50% inhibition of the shock-sensitive uptake of maltose, and a complete inhibition of the proton-symport uptake of lactose. Radical scavengers had little or no effect on the inhibition of these systems.

The effect of alterations in the fluidity and phase state of the membrane lipids on the passive permeation and facilitated diffusion of glycerol in Escherichia coli.

The passive permeation and facilitated diffusion of glycerol into Escherichia coli K 1060, an unsaturated fatty acid auxotroph, were studied as a function of temperature and membrane lipid fatty acid composition using a stopped-flow spectrophotometric assay of glycerol permeation. The relative rates of glycerol passive and mediated entry were both significantly influenced by the fluidity of the membrane lipids, increasing as the gel to liquid-crystalline phase transition midpoint temperature of the membrane lipids decreased. The rate of passive glycerol permeation, but not the rate of glycerol facilitated diffusion, decreased as the membrane lipids were converted to the gel state. The apparent activation energies for passive and facilitated diffusion of glycerol, measured in cells whose membrane lipids were in the liquid-crystalline state, were 15-16 and 10-11 kcal mol-1, respectively, and neither value was significantly influenced by the fatty acid composition or fluidity of the membrane lipids. The mechanistic implications of these observations for the function of the glycerol facilitated diffusion system of E. coli are discussed.

The effect of propranolol on the osmotic fragility of red cells and liposomes and the influence of the drug on glycerol transport across the membrane of red cells

Propranolol has been found to have different effects on the stability of red-cell membranes and model phospholipid membranes (liposomes). Its effect on red-cell membranes is biphasic. At lower concentrations the drug protects the cells from hypotonic haemolysis, whereas at high concentrations it promotes haemolysis. In contrast to red cells, liposomses were destabilized by propranolol. The lytic effect on lipid membranes was observed within the same concentration range of the drug at which it exerts an antihaemolytic effect on red cells. Propranolol has been shown also to perturb glycerol transport in red cells. It stimulates passive diffusion of glycerol into bovine red cells and inhibits facilitated diffusion in human red cells. The experimental results suggest that although both membrane lipids and proteins are involved in drug-membrane interaction, the crucial role in propranolol-induced red-cell membrane stabilization is played by the protein component.

Diffusion of glycerol into monolayer and suspension cultures of chinese hamster ovary cells: A two-compartment analysis

Diffusion of glycerol into monolayer and suspension cultures of chinese hamster ovary cells: A two-compartment analysis

Role of glycerol permeation in the bloodstream form of Trypanosoma brucei.

Under aerobic conditions, we have determined glycerol uptake in the long slender (LS) bloodstream form of Trypanosoma (Trypanozoon) brucei brucei by studying glycerophosphate accumulation in the parasites. The coupled enzyme theory applies to the permeation-phosphorylation sequence. Glycerol passage through the plasma membrane is asymmetric, the efflux process being favored over the influx process. No free diffusion of glycerol can be detected even under conditions under which free glycerol accumulates within the cells; most probably, glycerol permeation is mediated by a specific transport system. In the absence of respiratory activities, glycerol is known to be an end-product of T. brucei glycolysis; its production from glycerophosphate should allow ATP synthesis. The observed efflux of free glycerol following intracellular accumulation of glycerophosphate confirms the hypothesis that glycerol production occurs through reversal of glycerol kinase activity. We conclude that in vivo the role of the carrier-mediated asymmetric permeation process is to prevent inhibition of the reversal of the glycerol kinase-mediated reaction by removing free glycerol.

Stopped-Flow Spectrophotometric Assay of Glycerol Permeation in Escherichia coli: Applicability and Limitations

The passive permeation and facilitated diffusion of glycerol in various strains of Escherichia coli have been studied by stopped-flow spectrophotometry. Contrary to the prediction for glycerol entry by simple diffusion, the reciprocal relaxation time (1/tau, s-1) for the passive permeation of glycerol in cells grown in the presence of glucose was not constant but decreased as the glycerol concentration increased above 100 mM. This anomaly was not due to refractive index differences or to the presence of residual levels of the glycerol facilitator protein in non-induced cells. Although reciprocal relaxation times for glycerol-induced E. coli exhibited the expected elevation relative to non-induced cells, a similar anomalous decrease 1/tar (s-1) with increasing glycerol concentration was observed. In addition, at early times after suspension in dilute buffer, the 1/tau (s-1) values obtained for induced or non-induced E. coli swelling in glycerol were considerably greater than for organisms incubated in dilute buffer for longer times. We concluded that either this spectrophotometric technique was not monitoring solely the permeation of glycerol into E. coli, or concentrations of glycerol above 100 mM significantly perturbed the structure of the E. coli cell envelope.

The influence of anesthetics on glycerol and K + translocation across the membrane of red blood cells

A wide variety of chemically unrelated anesthetics protects red blood cells against osmotic hemolysis. The protective effects of most anesthetics are mutally additive, suggesting common rather than separate mechanisms of action. Other properties shared by these anesthetics are their inhibition of facilitated diffusion of glycerol into human erythrocytes and their stimulation of passive transport of this solute in bovine red blood cells. With respect to their influence on passive K + translocation. anesthetics can be divided into two groups. Neutral and anionic anesthetics cause in isotonic NaCl solutions a large K + loss and in hypotonic NaCl solutions a K + leakage which decreases rapidly with increasing cell volume. Cationic anesthetics have the opposite effect: no K + loss occurs at the optimal protective concentration, whereas at higher concentrations a K + leakage occurs which increases with increasing cell volume. The possible significance of these differences in action is discussed.

Cryoprotection—Permeant vs nonpermeant additives

Chinese hamster ovary cells (CHO) were preserved at low temperatures with permeating and nonpermeating solutes. By making use of the temperature dependence of the diffusion of glycerol into cells it was possible to use this compared as either one or the other of these 2 classes of cryoprotectant. It was found that cell recovery could be obtained after cooling to, and storage at subzero temperatures ranging from −30 to −196 °C, but whereas both types of cryoprotectant provided some protection at the lowest temperature, only permeant compounds were useful at the higher temperatures.

Na+-dependent and Na+-independent glycerol fluxes inHymenolepis diminuta (Cestoda)

1. Labeled glycerol influx (J G i ) in the cestode,Hymenolepis diminuta, occurs by diffusion and two mediated systems which were distinguished by their sensitivity to Na+ and inhibitors. The Na+-activated system had a maximal glycerol influx (J G i max) of 91.5 μmoles/g ethanol extracted dry wt/hr and an apparent transport constant (K t ) of 0.24 mM; fluxes of glycerol and Na+ did not appear to be coupled. The second transport system, which operated in the absence of external Na+, had aJ G i max of 83.8 μmoles/g ethanol extracted dry wt/hr and aK t of 0.69 mM (Figs. 1 and 2). 2. DL-β-glycerophosphate, glyceraldehyde, monoacetin, and phloretin inhibited both transport systems, while 1, 2-propanediol inhibited only the Na+-dependent system (Fig. 3). 3. The inhibition ofJ G i by DL-β-glycerophosphate was relieved by ammonium molybdate, adenosine triphosphate, adenosine monophosphate and glucose-6-phosphate (Fig. 4, Table 1). These compounds had little or no effect onJ G i indicating that inhibition was produced by glycerol liberated from the hydrolysis of the phosphorylated compound by surface phosphohydrolases of the worm. 4. Li+, K+, Tris and choline did not replace Na+ as an activator ofJ G i (Fig. 7). Glycerol diffusion rates in media where Li+ or K+ were used to replace Na+ were identical; however, replacement of Na+ with Tris lowered the diffusion rate (Table 2). Diffusion-corrected rates forJ G i were the same in Li+-, K+-, and Tris-substituted media, but were significantly lower in choline-substituted media; choline appeared to act as a competitive inhibitor of mediatedJ G i (Fig. 8, Table 2). 5. Phloretin competitively inhibitedJ G i while phlorizin had no effect. The effects of pH on the inhibition by phloretin indicated that the ketonic form, and not the enolic form, of phloretin was responsible for inhibition (Fig. 5).

Importance of facilitated diffusion for effective utilization of glycerol by Escherichia coli.

Wild-type Escherichia coli possesses an inducible permeation system which catalyzes facilitated diffusion of glycerol into the cell. A spectrophotometric method can be used to assess the presence of this mechanism. The structural gene for the facilitator (glpF) and the structural gene for glycerol kinase (glpK) apparently belong to a single operon. The glpF(+) allele permits effective glycerol utilization by the cells, and, at millimolar concentrations of glycerol, cells carrying the glpF(+) allele grow much faster than glpF genotypes. Although the glycerol-scavenging power of the cell depends both on the facilitated entry of the substrate and its subsequent trapping by an adenosine triphosphate-dependent phosphorylation, the two gene products, the facilitator and kinase, function independently. Wild-type Shigella flexneri appears to be glpK(+) but glpF. This organism grows slowly in media at low concentrations of glycerol. When the glpF(+) and glpK(+) alleles of E. coli are inserted into the S. flexneri genome by transduction, the hybrid strain grows rapidly in low glycerol medium. Vice versa, when the glpF and glpK(+) alleles of S. flexneri are incorporated into E. coli, the hybrid strain grows slowly in low glycerol medium.

Promoter-like mutant with increased expression of the glycerol kinase operon of Escherichia coli.

A glycerol-specific phenotypic revertant isolated from a mutant of Escherichia coli missing enzyme I of the phosphoenolpyruvate phosphotransferase system was studied. This revertant is capable of producing higher levels of glycerol kinase and the protein mediating the facilitated diffusion of glycerol (facilitator) than wild-type cells. The kinase of the revertant is indistinguishable from the wild-type enzyme with respect to its sensitivity to feedback inhibition by fructose-1,6-diphosphate, its pH optimum, and its turnover number. The synthesis of glycerol kinase in strains bearing the suppressor locus is resistant to catabolite repression. The suppressor mutation mapped at the known glpK locus. Thus, it is suggested that the mutation occurred in the promoter of the operon specifying the kinase and the facilitator.

Rate of intracellular diffusion as measured in barnacle muscle.

The rate of intracellular diffusion of water, urea, and glycerol was measured in the giant barnacle Balanus nubilus. The calculated diffusion coefficients were not different from those values reported for dilute solutions.

Diffusion in concentrated polymer solutions. I. A. An interferometric micromethod for diffusion measurements. B. Diffusion of sucrose in solutions of polyvinylpyrrolidone

AbstractA simple micromethod for the measurement of diffusion coefficients has been developed. The diffusion cell is a wedge of two partially reflecting microscope slides and the liquids to be examined are placed in the wedge. Typical results for the diffusion of glycerol against water and 10% sucrose against water are shown. The method is applied to the measurement of the diffusion of sucrose in various concentrations of polyvinylpyrrolidone using samples of three different molecular weights. The local relative viscosity, as given by the ratio of the diffusion constant in water to that in the polymer solution, is nearly unity for low concentrations of polymer but above a critical concentration rises to a value that is independent of molecular weight of the sample. The lower the molecular weight, the higher is the critical concentration and the more abruptly is the rise in local viscosity with polymer concentration. These results are explainable in terms of a random coil model if it is assumed that the critical concentration is reached when the molecules overlap to a small extent. The rise in local viscosity is attributed to an entanglement of the chain segments resulting finally in a loss of identity of the individual polymer molecules. Applications of these results to a theory of wet spinning of fibers are indicated.

Diffusion of organic molecules through wood

AbstractThe diffusion of alcohols, glycerol, phenol, formic, acetic and butyric acids through four species of Indian timbers in the water‐saturated condition has been studied and the results reported. In contrast to several inorganic ions, Fick's law is obeyed by the organic molecules in the concentrations studied. As is to be expected, the diffusion in the axial direction is several times that in the other directions. The speed of diffusion decreases rapidly with the molecular weight of the substance and the density of the wood. While in the case of the alcohols the logarithm of the diffusion constant varies as the molecular weight with the acids the diffusion constant is proportional to the molecular weight.