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J Gutknecht

Publications and source records attributed to J Gutknecht.

At least 37 records · Page 2Linked to original sources
PubMed1987

Proton conductance through phospholipid bilayers: water wires or weak acids?

The proton/hydroxide (H+/OH-) permeability of phospholipid bilayer membranes at neutral pH is at least five orders of magnitude higher than the alkali or halide ion permeability, but the mechanism(s) of H+/OH- transport are unknown. This review describes the characteristics of H+/OH- permeability and conductance through several types of planar phospholipid bilayer membranes. At pH 7, the H+/OH- conductances (GH/OH) range from 2-6 nS cm-2, corresponding to net H+/OH- permeabilities of (0.4-1.7) X 10(-5) cm sec-1. Inhibitors of GH/OH include serum albumin, phloretin, glycerol, and low pH. Enhancers of GH/OH include chlorodecane, fatty acids, gramicidin, and voltages greater than 80 mV. Water permeability and GH/OH are not correlated. The characteristics of GH/OH in fatty acid (weak acid) containing membranes are qualitatively similar to the controls in at least eight different respects. The characteristics of GH/OH in gramicidin (water wire) containing membranes are qualitatively different from the controls in at least four different respects. Thus, the simplest explanation for the data is that GH/OH in unmodified bilayers is due primarily to weakly acidic contaminants which act as proton carriers at physiological pH. However, at low pH or in the presence of inhibitors, a residual GH/OH remains which may be due to water wires, "hydrated defects," or other mechanisms.

Biological Transport↗
PubMed1987

Proton/hydroxide conductance and permeability through phospholipid bilayer membranes.

Proton/hydroxide (H+/OH-) permeability of phospholipid bilayers is several orders of magnitude higher than alkali or halide ion permeabilities at pH 7. The objective of this study was to determine the mechanism(s) of H+/OH- conductance and permeability through planar phospholipid bilayer membranes. Membranes were formed from decane solutions of bacterial phosphatidylethanolamine, diphytanoyl phosphatidylcholine, or egg phosphatidylcholine plus cholesterol. At pH 7, H+/OH- conductance (GH/OH) ranged from 2 to 6 nS.cm-2, corresponding to H+/OH- "net" permeabilities of (0.4-1.6) X 10(-5) cm.sec-1. GH/OH was inhibited by serum albumin (fatty acid-free), phloretin, and low pH. GH/OH was increased by chlorodecane, long-chain fatty acids, and voltages greater than 80 mV. Water permeability and GH/OH were not correlated. The results suggest that the H+/OH- charge carrier (i) is primarily anionic, (ii) crosses the membrane via nonpolar pathway(s), and (iii) can be removed from the membrane by "washing" with serum albumin. The simplest explanation is that the phospholipids contain weakly acidic contaminants that act as proton carriers at neutral pH. However, at low pH or in the presence of inhibitors, a "background" GH/OH remains that may be due to other mechanisms.

Electric Conductivity↗
PubMed1986

Permeability of small nonelectrolytes through lipid bilayer membranes.

Diffusion of small nonelectrolytes through planar lipid bilayer membranes (egg phosphatidylcholine-decane) was examined by correlating the permeability coefficients of 22 solutes with their partition coefficients between water and four organic solvents. High correlations were observed with hexadecane and olive oil (r = 0.95 and 0.93), but not octanol and ether (r = 0.75 and 0.74). Permeabilities of the seven smallest molecules (mol wt less than 50) (water, hydrofluoric acid, hydrochloric acid, ammonia, methylamine, formic acid and formamide) were 2- to 15-fold higher than the values predicted by the permeabilities of the larger molecules (50 less than mol wt less than 300). The "extra" permeabilities of the seven smallest molecules were not correlated with partition coefficients but were inversely correlated with molecular volumes. The larger solute permeabilities also decreased with increasing molecular volume, but the relationship was neither steep nor significant. The permeability pattern cannot be explained by the molecular volume dependence of partitioning into the bilayer or by the existence of transient aqueous pores. The molecular volume dependence of solute permeability suggests that the membrane barrier behaves more like a polymer than a liquid hydrocarbon. All the data are consistent with the "solubility-diffusion" model, which can explain both the hydrophobicity dependence and the molecular volume dependence of nonelectrolyte permeability.

Carbon Radioisotopes↗
PubMed1984

Monocarboxylic acid permeation through lipid bilayer membranes.

The membrane permeability coefficients for the homologous monocarboxylic acids, formic through hexanoic, as well as benzoic and salicylic, were determined for egg phosphatidylcholine-decane planar bilayer membranes. The permeabilities of formic, acetic and propionic acid were also determined for "solvent-free" phosphatidylethanolamine bilayers. Permeability coefficients were calculated from tracer fluxes measured under otherwise symmetrical conditions, and precautions were taken to ensure that the values were not underestimated due to unstirred layer effects. The relation between the nonionic (HA) permeability (Pm) and the hexadecane/water partition coefficient (Kp) was: log Pm = 0.90 log Kp + 0.87 (correlation coefficient = 0.996). Formic acid was excluded from the analysis because its permeability was sixfold higher than predicted by the other acids. The permeabilities for "solvent-free" membranes were similar to those for decane-containing membranes. The exceptionally high permeability of formic acid and the high correlation of the other permeabilities to the hexadecane/water partition coefficient is a pattern that conforms with other nonelectrolyte permeabilities through bilayers. Similarly, the mean incremental free energy change per methylene group (delta delta G/-CH2-) was -764 cal mol-1, similar to other homologous solutes in other membrane systems. However, much less negative delta delta G values (-120 to -400 cal mol-1) were previously reported for fatty acids permeating bilayers and biological membranes. These values are due primarily to unstirred layer effects, metabolism and binding to membranes and other cell components.

Benzoates↗
PubMed1984

Proton/hydroxide conductance through lipid bilayer membranes.

A simple method of measuring proton/hydroxide conductance (GH/OH) through planar lipid bilayer membranes is described. First the total conductance (Gm) is measured electrically. Then the H+/OH- transference number (TH/OH) is estimated from the diffusion potential (Vm) produced by a transmembrane pH gradient. The pH gradient is produced by a pair of buffered solutions which have identical concentrations of all ions except H+ and OH-. Thus, Vm is due entirely to H+/OH- diffusion and GH/OH can be calculated from the relations, Vm = TH/OHEH/OH and GH/OH = TH/OHGm, where EH/OH is the equilibrium potential for H+ and OH-. In bilayers made from bacterial phosphatidylethanolamine (PE) in n-decane, GH/OH is nearly independent of pH, ranging from about 10(-9) S cm-2 at pH 1.6 to 10(-8) S cm-2 at pH 10.5. Because GH/OH is nearly independent of pH, the calculated permeability coefficients to H+ and/or OH- are extremely pH dependent, which partly explains the wide range of values reported for phospholipid vesicles and biological membranes. GH/OH appears to be independent of the membrane surface charge, because titrating either the phosphate or the amino group of PE has little effect on GH/OH. GH/OH is reduced about 10-fold when the water activity is reduced 33% by replacement with glycerol. Although the mechanism of H+/OH- conductance is not known, the relation between GH/OH and water activity suggests that several water molecules are involved in the H+/OH- transport process.

Biological Transport↗
PubMed1983

Cadmium and thallous ion permeabilities through lipid bilayer membranes.

Cadmium (Cd2+) and thallous ion (Tl+) permeabilities were measured in planar (Mueller-Rudin) lipid bilayer membranes made from diphytanoylphosphatidylcholine in decane. Permeabilities of the electroneutral Cl- complexes, measured with tracers (109Cd and 204Tl), were about 10(-8) cm X s-1 for CdCl2 and 10(-6) cm X s-1 for TlCl. Electrical conductance measurements showed that permeabilities to Cd2+ and Tl+ were approx. 10(-11) cm X s-1, similar to the Na+ permeability. The low permeabilities to both Cd2+ and CdCl2 are consistent with biological studies which suggest that Cd transport and toxicity are protein mediated and correlated with Cd2+, not CdCl2, concentration. However, the low bilayer permeability to Tl+ raises questions about recent reports that Tl+ is a lipid permeable cation in biological membranes and liposomes. An alternative explanation for the lipid permeable behavior of Tl+ is presented, based on the diffusion of TlCl and other complexes of Tl+ with inorganic and organic anions.

Cadmium↗
PubMed1982

SCN-and HSCN transport through lipid bilayer membranes. A model for SCN- inhibition of gastric acid secretion.

Diffusion of thiocyanate (SCN-) and thiocyanic acid (HSCN) (pK=-1.8) through lipid bilayer membranes was studied as a function of pH. Membranes were made of egg phosphatidylcholine or phosphatidylcholine plus cholesterol (1:1 mol ratio) dissolved in decane or tetradecane. Tracer fluxes and electrical conductances were used to estimate the permeabilities to HSCN and SCN-. Over the pH range 1.0 to 3.3 only HSCN crosses the membrane at a significant rate. The relation between the total SCN flux (JA), concentrations and permeabilities is: 1/JA = 1/pul([A-]+[HA])+1/pm HA[HA], where [a-] and [HA] are the concentrations of SCN- and HSCN, pul is permeability coefficient of the unstirred layer, and PmHA is the membrane permeability to HSCN. By fitting this equation to the data we find that PmHA = 2.6 cm.s-1 and Pul = 9.0.10-4 cm .s-1. Conductance measurements indicate that PmA- is 5.10-9 cm.s-1. Addition of cholesterol to phosphatidylcholine (1:1 mol ratio) reduces PmHA by a factor of 0.4 but has no effect on PmA-. SCN- is potent inhibitor of acid secretion in gastric mucosa, but the mechanism of SCN- action is unknown. Our results suggest that SCN- acts by combining with H+ in the mucosal unstirred layer (secretory pits) and diffusing back into the cells as HSCN, thus dissipating the proton gradient across the secretory membrane. A similar mechanism of cation is proposed for some other inhibitors of gastric acid secretion, e.g. nitrite (NO2-), cyanate (CNO-) and NH4+.

Animals↗
PubMed1982

Weak acid permeability through lipid bilayer membranes. Role of chemical reactions in the unstirred layer.

The premeabilities of planar lipid bilayer (egg phosphatidylcholine-decane) membranes to butyric and formic acids were measured by tracer and pH electrode techniques. The purposes of the study were (a) to establish criteria for the applicability of each method and (b) to resolve a discrepancy between previously published permeabilities determined using the different techniques. Tracer fluxes of butyric acid were measured at several concentrations and pH's. Under symmetrical conditions the one-way flux of butyric acid(J) is described by 1/J = 1/Pul ([HA] + [A-]) + 1/Pm([HA]), where Pul and Pm are the unstirred layer and membrane permeability coefficients. Pm determined in this manner is 950 x 10(4) cm s-1. Published values for the butyric acid permeability for egg phosphatidylcholine-decane bilayers are 11.5 x 10(-4) (Wolosin and Ginsburg, 1975) and 640 x 10(-4) cm s-1 (Orbach and Finkelstein, 1980). Wolosin and Ginsburg measured net fluxes from a solution of pH = Pka into an unbuffered solution containing a pH electrode. Orbach and Finkelstein measured tracers fluxes under symmetrical conditions at pH 7.4. We reproduced the results of Wolosin and Ginsburg and showed that their apparently low Pm was caused by unstirred layer effects in their poorly buffered solutions. The permeability to formic acid (pKa = 3.75) measured by both tracer and pH electrode techniques was approximately 10(-2) cm s-1. However, if pm greater than Pul, the pH electrode technique cannot be used for measuring the permeabilities of weak acids with pKa's greater than approximately 4.

Alkanes↗
PubMed1981

Histamine, theophylline and tryptamine transport through lipid bilayer membranes.

Diffusion of histamine, theophylline and tryptamine through planar lipid bilayer membranes was studied as a function of pH. Membranes were made of egg phosphatidylcholine plus cholesterol (1 : 1 mol ratio) in tetradecane. Tracer fluxes and electrical conductances were used to estimate the permeabilities to nonionic and ionic species. Only the nonionic forms crossed the membrane at a significant rate. The membrane permeabilities to the nonionic species were: histamine, 3.5 x 10(-5) cm x s-1; theophylline, 2.9 x 10(-4) cm x s-1; and tryptamine, 1.8 x 10(-1) cm x s-1. Chemical reactions in the unstirred layers are important in the transport of tryptamine and theophylline, but not histamine. For example, as pH decreased from 10.0 to 7.5 the ratio of nonionic (B) to ionic (BH+) tryptamine decreased by 300-fold, but the total tryptamine permeability decreased only 3-fold. The relative insensitivity of the total tryptamine permeability to the ratio, [B]/[BH+], is due to the rapid interconversion of B and BH+ in the instirred layers. Our model describing diffusion and reaction in the unstirred layers can explain some 'anomalous' relationships between pH and weak acid/base transport through lipid bilayer and biological membranes.

Biological Transport↗
PubMed1981

Hydroxyl ion permeability of lipid bilayer membranes.

The OH- permeability of lipid bilayer (egg phosphatidylcholine-cholesterol) membranes was estimated from ionic transference numbers and membrane conductances at high pH. Membranes are slightly cation (Na+) selective over the pH range of 6--10. However, at pH greater than 11, Na+ and Cl- conductances decrease and OH- conductance increases so that the membrane becomes highly selective to OH-. From the OH- conductance we estimate the OH- permeability coefficient to be 1.8 . 10(-9) cm . s-1. The OH- selectivity of lipid bilayers may contribute to the observed H+/OH- selectivity of some biological membrane at high pH.

Chlorides↗
PubMed1981

Hydrofluoric and nitric acid transport through lipid bilayer membranes.

Hydrofluoric and nitric acid transport through lipid bilayer membranes were studied by a combination of electrical conductance and pH electrode techniques. Transport occurs primarily by nonionic diffusion of molecular HF and HNO3. Membrane permeabilities to HF and HNO3 ranged from 10(-4) to 10(-3) cm . s-1, five to seven orders of magnitude higher than the permeabilities to NO-3, F- and H+. Our results are consistent with the hypothesis that F- transport through biological membranes occurs mainly by nonionic diffusion of HF. Our results also suggest that of the two principal components of 'acid rain', HNO3 may be more toxic than H2SO4.

Cholesterol↗
PubMed1981

Transport of protons and hydrochloric acid through lipid bilayer membranes.

Transport of protons and hydrochloric acid through lipid bilayer membranes was studied by a combination of electrical conductance and pH electrode techniques. In the presence of large pH gradients, proton transport occurs primarily by diffusion of molecular HCl. The permeability of egg phosphatidylcholine/decane bilayers to HCl is about 3 cm . s-1, seven to nine order of magnitude higher than the permeability to H+, OH- or Cl-. The HCl permeability of phosphatidylserine or egg phosphatidylcholine/cholesterol (1 : 1) bilayers is about 50% lower than the permeability of egg phosphatidylcholine bilayers. Diffusion of molecular HCl may be an important process in tissues exposed to high HCl concentrations, e.g., gastric mucosa. However, at neutral pH the diffusion of molecular HCl is too slow to contribute significantly to net movements of H+ or Cl-.

Biological Transport↗
PubMed1980

Solubility of carbon dioxide in lipid bilayer membranes and organic solvents.

Partition coefficients of carbon dioxide into lipid bilayers (liposomes) and organic solvents were measured as a function of temperature. The molar partition coefficient of CO2 into liposomes of egg lecithin at 25 degrees C was 0.95 (ml CO2/ml lipid)/(ml CO2/ml saline). The addition of an equimolar amount of cholesterol to the egg lecithin decreased the partition coefficient by about 25%. The partition coefficients for CO2 into liposomes at 25 degrees C were lower than the partition coefficients into octanol (1.3), hexadecane (1.5) and olive oil (1.7). The results are discussed in terms of the solubility-diffusion model of non-electrolyte transport through lipid bilayer membranes.

Carbon Dioxide↗
PubMed1979

Coupled transport of protons and anions through lipid bilayer membranes containing a long-chain secondary amine.

Transport of protons and halide ions through planar lipid bilayers made from egg lecithin and a long-chain secondary amine (n-lauryl [trialkylmethyl] amine) in n-decane was studied. Net proton fluxes were measured with a pH electrode, and halide fluxes were measured with 82Br- and 36Cl-. In membranes containing the secondary amine, a large net proton flux was produced either by a Br- gradient with symmetrical pH or by a pH gradient with symmetrical Br-, but not by a pH gradient in Br--free solutions. This H+ flux was electrically silent (nonconductive), and the H+ permeability coefficient was greater than 10(-3) cm sec-1 in 0.1 M NaBr. In Br--free solutions, H+ selectivity was observed electrically by measuring conductances and zero-current potentials generated by H+ activity gradients. The permeability coefficient for this ionic (conductive) H+ flux was about 10(-5) cm sec-1, several orders of magnitude smaller than the H+ permeability of the electroneutral pathway. Large electroneutral Br- exchange fluxes occurred under symmetrical conditions, and the permeability coefficient for Br- exchange was about 10(-3) cm sec-1 at pH 5. The one-way Br- flux was inhibited by substituting SO4= for Br- on the "trans" side of the membrane. These results support a "titratable carrier" model in which the secondary amine exists in three forms (C, CH+ and CHBr). Protons can cross the membrane either as CHBr (nonconductive) or as CH+ (conductive), whereas Br- crosses the membrane primarily as CHBr (nonconductive). In addition to these three types of transport, there is also a pH-dependent conductive flux of Br- which has a permeability coefficient of about 10(-7) cm sec-1 at pH 5. Experiments with lipid monolayers suggest that the pH dependence of this conductive flux is caused by a change in surface potential of about +100 mV between pH 9.5 and 5.0.

Amines↗