Effect of the lipid phase transition on the kinetics of H+/OH- diffusion across phosphatidic acid bilayers

The kinetics of H+/OH- diffusion across dimyristoyl phosphatidic acid bilayer membranes was measured by following the absorbance of the pH-sensitive indicator Cresol red (o-cresolsulfonphthalein) entrapped in single lamellar vesicles after rapidly changing the external pH in a stopped-flow apparatus. The H+/OH- permeability coefficient was found to be in the 10(-5) to 10(-3) cm . s-1 range. The lipid phase transition has a strong influence on the permeation kinetics as the permeability coefficients in the liquid-crystalline phase are drastically higher. The permeability shows no maximum at the phase transition temperature as is the case for other ions, but displays a similar temperature dependence as water permeation. This is also reflected in the high activation energy of approx. 20 kcal/mol and supports the hypothesis (Nichols, J.W. and Deamer, D.W. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 2038-2042) of H+/OH- permeation via hydrogen bonded water molecules. A second slower kinetic phase is also observed, where the permeation is obviously controlled by counterion diffusion. The temperature dependence of this slow process displays the for ion diffusion characteristic maximum in the permeability at the phase-transition temperature.     

Posteroventral medial pallidotomy in levodopa-unresponsive parkinsonism

PURPOSE: The purpose of this study was to test whether structural modifications improve the intestinal absorption of DMP 728 (cyclo(D-Abu-NMeArg-Gly-Asp-Amb)), a GPIIb/IIIa receptor antagonist. METHODS: In vitro permeabilities of prodrugs and analogs of DMP 728 across excised rat intestinal segments were determined. RESULTS: n-Butyl and n-octyl esters of DMP 728 were relatively stable during in vitro permeation of rat intestine. Intestinal permeation rates of these compounds were no greater than that of DMP 728, even though the octyl ester was much more lipophilic. A pivaloyloxymethyl ester, which was hydrolyzed to DMP 728 during intestinal permeation, also did not improve permeability. In another approach, analogs with an additional methyl substituent on various amide nitrogens were evaluated. Cyclo(D-Val-NMeArg-Gly-Asp-NMeAmb), cyclo(D-Abu-diN-MeLys-Gly-Asp-Amb), and cyclo(NMeGly-NMeArg-Gly-Asp-Amb) each had about 2-fold greater permeability than DMP 728. Two other analogs with improved permeability were linear Ac-D-Abu-NMeArg-Gly-Asp-Amb and a DMP 728 derivative in which the Asp was rearranged. An analog in which the charged amino acids were replaced by neutral amino acids had permeability similar to DMP 728. CONCLUSIONS: Within this series of peptides, hydrogen bonding tendency and structural constraint influenced intestinal permeation, but not always in ways consistent with the literature, whereas charge and lipophilicity were not shown to influence intestinal permeability. The failure of these approaches to improve permeation more significantly could be due to the influence of secretory transport.     

Transdermal delivery of narcotic analgesics: comparative metabolism and permeability of human cadaver skin and hairless mouse skin

The permeation of hairless mouse skin and human cadaver skin by narcotic analgesics was investigated to determine the interspecies variation. Permeability coefficients of morphine, fentanyl, and sufentanil across full-thickness hairless mouse skin were 1 order of magnitude higher than those found for human epidermis. The permeability coefficient of morphine for stripped hairless mouse skin was 500-fold higher than that for intact skin, showing the stratum corneum to be the principal barrier to its penetration. The permeability coefficient of fentanyl for stripped hairless mouse skin was also raised, but stripping caused an inappreciable increase in the permeation rate of sufentanil. The thick dermis of excised mouse skin obviously offered a significant resistance to the permeation of these lipophilic compounds. In comparison, the permeability coefficients of fentanyl and sufentanil through stripped cadaver epidermis (n > or = 25) were 67 and 37 higher than for intact human epidermis, respectively. The skin metabolism of the narcotics was investigated. No significant metabolic degradation of morphine, fentnayl, and sufentanil was observed in either fresh human cadaver skin or hairless mouse skin homogenates in the presence of NADPH cofactor, suggesting a low monooxygenase enzyme presence in skin. Moreover, no measurable glucuronidation of morphine took place in human skin or hairless mouse skin. Both processes proceeded rapidly in liver homogenates (mouse) under identical circumstances. It thus appears that these drugs pass through in intact form.     

A 1H-NMR study of the permeation of glycolic acid through phospholipid membranes

The transmembrane permeability coefficient of the alpha-hydroxyacid, glycolic acid, has been measured for egg phosphatidylcholine large unilamellar vesicles. The determination of the vesicle concentration independent first-order rate constant for membrane transport and the permeability coefficient were made using an NMR technique employing shift agents. Both the temperature dependence and the dependence on cholesterol content were investigated. The activation energy and the Arrhenius pre-exponential factor were found to be dependent on the cholesterol content. A marked increase in both parameters was observed up to 20 mol% cholesterol, with a further, small increase up to 50%. The pH dependence of permeability was also investigated. An increase in permeability is observed with a decrease in pH, providing a possible explanation for the effectiveness of glycolic acid in skin treatment.     

Angiotensin II stimulation of the stress-activated protein kinases in renal mesangial cells is mediated by the angiotensin AT1 receptor subtype

Poly(acrylic acid) gels containing 5-fluorouracil (5-FU) and tetrahydrogeraniol (THG) were prepared and the effects of THG on 5-FU permeation across the excised rat skin were studied by in vitro methods. Experiments on in vitro permeation of 5-FU across the skin with vertical diffusion cells showed that addition of THG to the gels markedly enhanced the 5-FU permeability. Increasing the THG concentration in the gels to 8% proportionally increased the permeability of 5-FU. More than 12 h was required to reach a steady-state level of 5-FU after administration of 5-FU-THG gel topically. The permeability parameters such as flux, permeability coefficient and enhancement ratio were determined. The results indicated a maximum flux of 252.91+/-9.61 microgram/cm2 per h, and the enhancement ratio of 31.22+/-1.18 when the THG concentration was 8%. Synergistic effects of propylene glycol (PG) with THG were also investigated and a maximum flux of 256.81+/-9.15 microgram/cm2 per h, was obtained when the PG concentration was 5% and THG was 8%. The corresponding enhancement ratio was 31.71+/-1.13. These results suggest not only that THG would be very useful for increasing the skin permeability of 5-FU, but also that THG being a natural product might be useful for developing transdermal therapeutic systems for the delivery of practically unabsorbable drugs.     

Optimal flow rates for integrated cardioplegia

We have examined whether the anionic amino acids, glutamate and aspartate, permeate through the same volume-regulated conductance permeant to Cl- ions. Cell swelling was initiated in response to establishing a whole-cell configuration in the presence of a hyposmotic gradient. Volume-regulated anion currents carried by Cl-, glutamate, or aspartate developed with similar time courses and showed similar voltage-dependent inactivation. Permeability ratios (Paa/PCl) calculated from measured reversal potentials were dependent on the mole fraction ratio (MFR) of the permeant anions ([aa]/([aa] + [Cl-])). MFR was varied from 0.00 to 0.97. As the fraction of amino acid increased, Paa/PCl decreased. Current amplitude was similarly dependent on MFR. These results show that the permeation of anionic amino acids and that of Cl- ions are not independent of each other, indicating that the ion channel underlying the volume-regulated conductance can be occupied by more than one ion at a time. Application of Eyring rate theory indicated that the major barrier to Cl- ion permeation is at the intracellular side of the membrane, and that the major barrier to amino acid permeation is at the extracellular side of the membrane. The interactions between these permeant ions may have a physiological modulatory role in volume regulation through a volume-regulated anion conductance.     

Transbuccal delivery of acyclovir: I. In vitro determination of routes of buccal transport

PURPOSE: To determine the major routes of buccal transport of acyclovir and to examine the effects of pH and permeation enhancer on drug permeation. METHODS: Permeation of acyclovir across porcine buccal mucosa was studied by using side-by-side through diffusion cells at 37 degrees C. The permeability of acyclovir was determined at pH range of 3.3 to 8.8. Permeability of different ionic species was calculated by fitting the permeation of data to a mathematical model. Acyclovir was quantified using HPLC. RESULTS: Higher steady state fluxes were observed at pH 3.3 and 8.8. The partition coefficient (1-octanol/buffer) and the solubility of acyclovir showed the same pH dependent profile as that of drug permeation. In the presence of sodium glycocholate (NaGC) (2-100 mM), the permeability of acyclovir across buccal mucosa was increased 2 to 9 times. This enhancement was independent of pH and reached a plateau above the critical micelle concentration of NaGC. The permeabilities of anionic, cationic, and zwitterionic species were 3.83 X 10-5, 4.33 X 10-5, and 6.24 x 10-6 cm/sec, respectively. CONCLUSIONS: The in vitro permeability of acyclovir across porcine buccal mucosa and the octanol-water partitioning of the drug were pH dependent. A model of the paracellular permeation of the anionic, cationic, and zwitterionic forms of acyclovir is consistent with these data. The paracellular route was the primary route of buccal transport of acyclovir, and the enhancement of transbuccal transport of acyclovir by sodium glycocholate (NaGC) appeared to operate via this paracellular route.     

Levels of H+ and other monovalent cations in dormant and germinating spores of Bacillus megaterium

Previous investigators using the extent of uptake of the weak base methylamine to measure internal pH have shown that the pH in the core region of dormant spores of Bacillus megaterium is 6.3 to 6.5. Elevation of the internal pH of spores by 1.6 U had no significant effect on their degree of dormancy or their heat or ultraviolet light resistance. Surprisingly, the rate of methylamine uptake into dormant spores was slow (time for half-maximal uptake, 2.5 h at 24 degrees C). Most of the methylamine taken up by dormant spores was rapidly (time for half-maximal uptake, less than 3 min) released during spore germination as the internal pH of spores rose to approximately 7.5. This rise in internal spore pH took place before dipicolinic acid release, was not abolished by inhibition of energy metabolism, and during germination at pH 8.0 was accompanied by a decrease in the pH of the germination medium. Also accompanying the rise in internal spore pH during germination was the release of greater than 80% of the spores K+ and Na+. The K+ was subsequently reabsorbed in an energy-dependent process. These data indicate (i) that between pH 6.2 and 7.8 internal spore pH has little effect on dormant spore properties, (ii) that there is a strong permeability barrier in dormant spores to movement of charged molecules and small uncharged molecules, and (iii) that extremely early in spore germination this permeability barrier is breached, allowing rapid release of internal monovalent cations (H+, Na+, and K+).     

Transfer RNA mimicry in a new group of positive-strand RNA plant viruses, the furoviruses: differential aminoacylation between the RNA components of one genome

The effects of the organic calcium channel blocker verapamil and the beta-receptor blocker propranolol on dipole (phi(d)) and surface (phi(s)) potentials of bilayer lipid membranes were studied. The boundary potentials (phi(b)= phi(d) + phi(s)) of black lipid membranes, monitored by conductance measurements in the presence of nonactin and by capacitive current measurements were compared with phi(s) calculated from the electrophoretic mobility of lipid vesicles. It was shown that the increase of boundary potential, induced by the adsorption of the positively charged propranolol, was caused solely by an increase in surface potential. Although phi(s) also increases due to the adsorption of verapamil, phi(b) diminishes. A sharp decrease of the dipole potential was shown to be responsible for this effect. From Langmuir adsorption isotherm the dissociation constant Kd of verapamil was estimated. The uncharged form of verapamil (Kd=(0.061+/-0.01) mM at pH 10.5) has a tenfold higher affinity to a neutral bilayer membrane than the positively charged form. The alteration of membrane dipole potential due to verapamil adsorption may have important implications for both membrane translocation and partitioning of small or hydrophobic ions and charged groups of membrane proteins.     

Management of adrenal cysts

Electrophoretic mobility data of SR vesicles reconstituted with uncharged and two mixtures of charged and uncharged lipids (Brethes, D., Dulon, D., Johannin, G., Arrio, B., Gulik-Krzywicki, T., Chevallier, J. 1986. Study of the electrokinetic properties of reconstituted sarcoplasmic reticulum vesicles. Arch. Biochem. Biophys. 246:355-356) were analyzed in terms of four models of the membrane-water interface: (I) a smooth, negatively charged surface; (II) a negatively charged surface of lipid bilayer covered with an electrically neutral surface frictional layer; (III) an electrically neutral lipid bilayer covered with a neutral frictional layer containing a sheet of negative charge at some distance above the surface of the bilayer; (IV) an electrically neutral lipid bilayer covered with a homogeneously charged frictional layer. The electrophoretic mobility was predicted from the numerical integration of Poisson-Boltzmann and Navier-Stokes equations. Experimental results were consistent only with predictions based on Model-III with charged sheet about 4 nm above the bilayer and frictional layer about 10 nm thick. Assuming that the charge of the SR membrane is solely due to that on Ca++-ATPase pumps, the dominant SR protein, the mobility data of SR and reconstituted SR vesicles are consistent with 12 electron charges/ATPase. This value compares well to the net charge of the cytoplasmic portion of ATPase estimated from the amino acid sequence (-11e). The position of the charged sheet suggests that the charge on the ATPase is concentrated in the middle of the cytoplasmic portion. The frictional layer of SR can be also assigned to the cytoplasmic portion of Ca++-ATPase. The layer has been characterized with hydrodynamic shielding length of 1. 1 nm. Its thickness is comparable to the height of the cytoplasmic portion of Ca++-ATPase.     

Synthesis and effect of two new penetration enhancers on the transdermal delivery of 5-fluorouracil through excised rat skin

The tetrahydrogeraniol (THG) derivative, ethyl-(3,7-dimethyl octyl thio) acetate (EDOTA) was prepared by reacting tetrahydrogeranyl bromide (obtained by reaction of 40% hydrobromic acid and concentrated sulfuric acid) with ethyl 2-mercaptoacetate, while 3,7-dimethyl octyl propionate (DOP) was synthesized by a common esterification reaction by reacting THG with propionic acid in the presence of cyclohexane and concentrated sulfuric acid. The penetration-enhancing effect of the new enhancers were compared with THG and Azone in vitro using excised rat skin in modified Franz-type diffusion cells. 5-Fluorouracil (5-FU), a hydrophilic drug with poor skin permeability was used as a model permeant. Skin samples were pretreated with pure liquid enhancers for 12 h. 5-FU flux through the control and enhancer-treated skin increased linearly with its concentration in the receptor compartment. EDOTA and DOP interacted with the skin rapidly (< 2h), and the duration of action is at least 24 h. Significant differences were found in the flux values of 5-FU; EDOTA and DOP enhanced the permeability of the drug about 6-fold and 11-fold respectively. Increased partition coefficient and diffusion coefficient values were obtained by these enhancers. The results suggested that the amount of EDOTA and DOP in the skin, especially in the stratum corneum, may be related to their penetration-enhancing effect.     

Electron capture gas chromatography of nanogram amounts of tertiary amines as trichloroethyl carbamates

The overall permeability of epithelial tissues to solutes is generally determined by analyzing net or unidirectional transepithelial fluxes in response to transepithelial differences of concentration and/or electrical potential using relations that describe diffusional movements across a single membrane. If the solute is uncharged and diffusional movements are transcellular, the overall transepithelial permeability coefficient is determined by the permeabilities of the two limiting cell membranes combinded in series. However, if the solute is charged and the pathway for transepithelial movement involves diffusional flows across at least two membranes arranged in series (i.e. transcellular transport), the value of the overall transepithelial permeability coefficient determined using relations that describe ionic diffusion across a single membrane is not an accurate measure of the permeabilities of the two limiting membranes combined in series. Further, if ionic diffusion is transcellular, permeability coefficients determined from studies of transepithelial fluxes are not only quantitatively incorrect but can also result in grossly erroneous interpretations of changes in transepithelial permeabilities and faulty inferences regarding the route of transepithelial ionic diffusion.     

酸性环境下黏土渗透特性的试验分析

文中以矿山蓄污土石坝黏土为原料,对其进行了在酸性环境下渗透特性的试验分析。试验表明,黏土在酸性环境下渗透系数会随着时间的推移而增加,在20%硫酸溶液条件下浸泡一周,黏土的渗透系数增加了约两倍,并且渗透系数的增加与酸性的强弱成正相关。试验还发现,黏土在酸性环境下会随着时间的推移而有失重的现象,说明酸性溶液对黏土有溶蚀作用,且浓度愈大作用愈强,致使黏土的孔隙增加,这也是渗透系数增加的原因。黏土渗透特性试验结果对进一步研究和精确预测矿山蓄污土石坝的剩余寿命具有重要意义。     

Characterization of convective solvent flow during iontophoresis

During iontophoresis under neutral pH conditions, there is a net convective flow of volume (electroosmosis) from anode to cathode leading to the enhanced transport of dissolved polar (but uncharged) solutes in the same direction. The objective of this study was to address the following unresolved questions with respect to electroosmotic transport: [1] Whether the efficiency of electroosmotic transport is solute size-dependent and, if so, how severe is this dependence? [2] Is electroosmosis linearly related to current density in the same way that the iontophoretic flux of charged species appears to be? [3] Are positively charged permeants able to influence their own electrotransport across the skin (by modifying the net charge on the membrane and altering, as a result, the permselectivity) and, if so, why and to what extent? Electroosmosis was assessed from the iontophoreically driven fluxes of mannitol, sucrose and lactose across hairless mouse skin in vitro. It was found that:- (a) The electroosmotic transport rate of mannitol is similar to that of the disaccharides, sucrose and lactose, when examined under identical conditions. The dependence of electroosmotic flux upon molecular size requires study of solutes having a wider range of MW than those considered here. (b) Electroosmotic flow from anode-to-cathode increases with applied current density; similarly, convective flow in the opposite direction diminishes with increasing current density. Apparently, there is correlation between the net movement of solvent and the total flux of ions across the skin. (c) The permselectivity of skin can be 'neutralized' by driving, iontophoretically, a cationic, lipophilic peptide (specifically the leutinizing hormone releasing hormone (LHRH) analog, Nafarelin) into the membrane.(ABSTRACT TRUNCATED AT 250 WORDS)     

Difference in the enhancing effects of ultrasound on the skin permeation of polar and non-polar drugs

The effect of ultrasound (150 kHz, 111 mW/cm2) on the permeability of isosorbide dinitrate (ISDN) and antipyrine (ANP) through excised hairless rat skin was evaluated using an Arrhenius plot. The permeability coefficients of ISDN across skin (at various temperatures) in the presence and absence of ultrasound were virtually isolinear on the Arrhenius plot. It has been suggested that the temporal increase in the ISDN flux, which was observed when ultrasound was applied in our previous study, was only a result of the thermal effect of ultrasound, i.e., an increase in the temperature of the donor solution. On the other hand, ultrasound influenced the Arrhenius plot of ANP, suggesting that the enhancement effect for ANP permeation could be not explained only by the thermal effect of ultrasound. In addition, the effective diffusion (D) and partition coefficients (K) of ISDN and ANP were estimated using their skin permeation profiles across the ultrasonic pretreated skin. The coefficients of ISDN with ultrasonic pretreatment were comparable to those without pretreatment. On the other hand, the D value of ANP with ultrasonic pretreatment was increased about 4 times by ultrasonic pretreatment, in spite of an insignificant change in the K value. These results suggest that the ultrasound used in the present study increased the effective diffusivity across the aqueous region in the stratum corneum to enhance the skin permeation of the polar compound, ANP.     

Permeabilities of alkyl p-aminobenzoates through living skin equivalent and cadaver skin

The in vitro permeabilities of alkyl p-aminobenzoates through living skin equivalent (LSE) and cadaver skin were compared. Methyl, ethyl, and butyl p-aminobenzoates were used as model compounds. The permeabilities of these compounds through LSE and cadaver skin from an aqueous drug suspension were determined with a flow-through diffusion cell. The permeability coefficients of these esters in LSE were an order of magnitude higher than in cadaver skin. This was primarily because of low resistances offered by the outermost layer (i.e., stratum corneum) of LSE. In the case of cadaver skin, the permeability coefficient increased as the carbon chain length increased, whereas no appreciable change in the permeability coefficients of these esters in LSE was observed. These results clearly suggest that the LSE membrane offered very little resistance as opposed to cadaver skin. Therefore, the LSE membrane may not quantitatively represent a good human skin model for evaluating skin permeation of a drug from topical or transdermal formulations.     

颗粒迁移和离子吸附对粗粒土渗透性的影响试验研究

为了研究颗粒迁移和氨氮离子吸附对粗粒土渗透性的影响,利用渗透仪对3种不同细粒含量的花岗岩全风化粗粒土进行渗透试验.研究3种土样分别在蒸馏水和硫酸铵溶液环境中的渗透系数变化规律.结果表明,在蒸馏水渗透环境中,随着土样中细颗粒含量的增加,颗粒迁移对土样渗透性的影响将有所减弱;在氨氮溶液环境中,氨氮吸附对细颗粒含量更高土样的渗透性影响更为明显;随着渗透时间延长,不同溶液环境中土样的渗透系数趋于一致,表明细颗粒迁移对土样渗透性的影响较氨氮离子吸附更强,但离子吸附对渗透系数降低具有一定的延迟效应.在此基础上,讨论土样在渗透过程中渗透性的演变机理,表明颗粒迁移造成土样下游孔隙堵塞,以及氨氮离子吸附造成颗粒表面水化膜厚度的变化,均是引起土样渗透性变化的主要原因.      

Effects of introduced aspartic and glutamic acid residues on the P'1 substrate specificity, pH dependence and stability of carboxypeptidase Y

Carboxypeptidase Y is a serine carboxypeptidase isolated from Saccharomyces cerevisiae with a preference for C-terminal hydrophobic amino acid residues. In order to alter the inherent substrate specificity of CPD-Y into one for basic amino acid residues in P'1, we have introduced Asp and/or Glu residues at a number of selected positions within the S'1 binding site. The effects of these substitutions on the substrate specificity, pH dependence and protein stability have been evaluated. The results presented here demonstrate that it is possible to obtain significant changes in the substrate preference by introducing charged amino acids into the framework provided by an enzyme with a quite different specificity. The introduced acidic amino acid residues provide a marked pH dependence of the (kcat/Km)FA-A-R-OH/(kcat/Km)FA-A-L-OH ratio. The change in stability upon introduction of Asp/Glu residues can be correlated to the difference in the mean buried surface area between the substituted and the substituting amino acid. Thus, the effects of acidic amino acid residues on the protein stability depend upon whether the introduced amino acid protrudes from the solvent accessible surface as defined by the surrounding residues in the wild type enzyme or is submerged below.     

Pharmacological modulation of endothelial function by insulin in the rat aorta

The aim of this study was to investigate the transdermal iontophoresis of a newly designed capsaicin derivative, sodium nonivamide propionate (SNP). The iontophoretic permeation of SNP from various pH buffers increased following the decrease of pH values. This trend was consistent with that of sodium nonivamide acetate (SNA) which is another synthetic analogue of capsaicin. However, the iontophoretic permeability of SNP was much lower than that of SNA. SNP was also delivered iontophoretically from hydrogel formulations. It is suggested that ionizable polymers should be avoided for iontophoretic delivery to maintain good penetration capacity of drugs. Both nonionic cellulose polymers of methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC) showed higher iontophoretic flux for SNP than the others did. Furthermore, the flux of SNP leveled off with an increase in the amount of polymers in hydrogel, indicating that the viscosity of vehicles plays an important role in the permeation of SNP. Comparing the various iontophoretic application modes, the discontinuous on/off cyclic mode showed higher penetration capacity than did the continuous mode although they possessed the same electrical energy. Moreover, the desorption time of SNP from skin was approximately 20 min which was longer than that of SNA.     

质子交换膜电解制氢氢气渗透研究进展

由于膜的吸水特性,高压质子交换膜(PEM)制氢（尤其是差压式,氢侧高压/氧侧常压）存在氢气渗透问题,影响电解堆的运行安全与效率。基于菲克定律描述的渗透通量与渗透率、分压差的关系,综述了温度/压力、膜水合程度、氢气分压差对氢气渗透的影响规律。在常规运行压力范围（3.5 MPa）内,扩散系数与溶解度主要受温度影响,温度升高则渗透率增大;氢气渗透率随膜水合程度的增加而增大;氢气分压差对渗透的影响表现出线性（渗透池环境）与非线性（电解制氢环境）两种关系,非线性可能源于膜透水性提升与水通道结构改变引起的对流渗透。考虑到电解制氢实际工况存在电流,综述了电流密度对氢渗透的影响,氢气渗透率随运行电流密度的升高而增大,氢过饱和是可能的影响机理,高电流密度下氢过饱和度升高,导致氢气通过膜的渗透增加。