Effects of cations on dipalmitoyl phosphatidylcholine/cholesterol/water systems

X-ray diffraction studies have been made on the effects of cations upon the dipamitoyl phosphatidylcholine/water system, which originally consists of a lamellar phase with period of 64.5 Å and of excess water. Addition of 1 mM CaCl₂ destroys the lamellar structure and makes it swell into the excess water. the lamellar phase, however, reappears when the concentration of CaCl₂ increases: a partially disordered lamellar phase with the repeat distance of 150–200 Å comes out at the concentration of about 10 mM, the lamellar diffraction lines become sharp and the repeat distance decreases with increasing CaCl₂ concentration. A small amount of uranyl acetate destroys lamellar phase in pure water. MgCl₂ induces the lamellar phase of large repeat distance, whereas LiCl, NaCl, KCl, SrCl₂ and BaCl₂ exhibit practically no effect by themselves. Addition of cholesterol to the phosphatidylcholine bilayers tends to stabilize the lamellar phaseThe high-angle reflections indicate that molecular arrangements on phosphatidylcholine bilayers change at CaCl₂ concentrations around 0.5 M. The bilayers at high CaCl₂ concentration seem to consist of two phases of pure phosphatidylcholine and of equimolar mixture of phosphatidylcholine and cholesterol.     

Conformational change of poly-N epsilon-glutaryl-L-lysine and poly-N epsilon-succinyl-L-lysine in aqueous salt solutions

The conformational changes of poly-N^ε-glutaryl-L -lysine (PGL) and poly-N^ε-succinyl-L -lysine (PSL) in various salt solutions were studied by use of ORD and potentiometric titration measurements. The addition of alkali metal salts to the fully ionized PGL or PSL solution caused helix formation. The helical content of the polymers increases in the following sequences: at salt concentration 0–2 M, CsCl < KCl < LiCl < NaCl; and at 2–3 M, LiCl < CsCl < KCl ～ NaCl. The preferential binding of the solvent components with various alkali metal salts of PGL or PSL was measured in LiCl, NaCl, and KCl solutions by means of equilibrium dialysis and differential refractometry. It was found that with increasing salt concentration, the polymers were preferentially hydrated in NaCl and KCl soultions; however the salt was preferentially bound to the polymers in LiCl solution. Such preferential binding was suggested to be closely related to conformational change. The addition of CaCl₂ to polymer solutions led to the stabilization of the helical structure of PGL or PSL.     

MICRURGICAL STUDIES IN CELL PHYSIOLOGY : V. THE ANTAGONISM OF CATIONS IN THEIR ACTIONS ON THE PROTOPLASM OF AM?BA DUBIA.

I. The Plasmalemma. 1. On the plasmalemma of amebæ CaCl₂ antagonizes the toxic action of LiCl better than it does NaCl, and still better than it does KCl. MgCl₂ antagonizes the toxic action of NaCl better than it does LiCl and still better than it does KCl. 2. CaCl₂ antagonizes the toxic action of LiCl and of KCl better than does MgCl₂: MgCl₂ antagonizes NaCl better than does CaCl₂. II. The Internal Protoplasm. 3. The antagonizing efficiency of CaCl₂ and of MgCl₂ are highest against the toxic action of KCl on the internal protoplasm, less against that of NaCl, and least against that of LiCl. 4. CaCl₂ antagonizes the toxic action of LiCl better than does MgCl₂: MgCl₂ antagonizes the toxic action of NaCl and of KCl better than does CaCl₂. 5. LiCl antagonizes the toxic action of MgCl₂ on the internal protoplasm more effectively than do NaCl or KCl, which have an equal antagonizing effect on the MgCl₂ action. III. The Nature of Antagonism. 6. When the concentration of an antagonizing salt is increased to a toxic value, it acts synergistically with a toxic salt. 7. No case was found in which a potentially antagonistic salt abolishes the toxic action of a salt unless it is present at the site (surface or interior) of toxic action. 8. Antagonistic actions of the salts used in these experiments are of differing effectiveness on the internal protoplasm and on the surface membrane.     

THE VAPOUR PRESSURES OF AQUEOUS SOLUTIONS WITH SPECIAL REFERENCE TO THE PROBLEM OF THE STATE OF WATER IN BIOLOGICAL FLUIDS

Data for the depression of vapour pressure are presented for the following aqueous solutions: NaCl (0.03 to 0.1 molar), KCl (0.03 to 0.1 molar), urea (0.05 to 0.5 molar), sucrose (0.05 to 0.10 molar), lactic and succinic acids, creatine, CaCl₂ (0.05 molar), and mixtures of these substances with one another and with certain other solutions (gelatin, gum acacia, sea water, LiCl, etc.). The relation of the depression of vapour pressure of a mixed solution to that of solutions of the individual constituents was investigated in order to ascertain to what extent such studies may be used for the determination of the degree of hydration, or of the state of water, in solutions. Organic substances (urea, sucrose, etc.) showed anomalous results which were markedly affected and unpredictable in mixed solutions. They are, therefore, unsuited for the study of water binding. In the case of solutions of inorganic substances—LiCl and CaCl₂—the principle of the additive nature of colligative properties is also only approximately true—except perhaps in very dilute solutions. The limitations of the colligative method for determining the degree of hydration have been defined in accord with the above findings. Studies of the vapour pressures of mixtures of gelatin or gum acacia with NaCl or KCl demonstrated that hydration in gelatin is relatively small at pH = 7 and undetectable in gum acacia solutions. The view, therefore, that hydrophilic colloids are strongly hydrated has not been substantiated. The passage from the sol to the gel state also was not accompanied in gelatin or in blood by any appreciable change in the degree of hydration of the hydrophilic colloids present in these substances.     

Electrophysiological responses of galeal contact chemoreceptors of Apis mellifera to selected sugars and electrolytes

Using conventional electrophysiological methods, the galeal sensilla chaetica of the honey bee, Apis mellifera, responded linearly to the log of solute concentrations of sucrose, glucose, fructose, NaCl, KCl, and LiCl but not to CaCl₂ or MgCl₂, which failed to give consistent responses. These sensillae had much higher firing rates for sugar than salt solutions; their relative responses to lower concentrations being NaCl < KCl < LiCl ? fructose < glucose ? sucrose. At higher concentrations NaCl < LiCl < KCl ? glucose < fructose ? sucrose. Four different spike types were seen. The first type had the highest amplitude and resulted from sugar stimulation. The second type had a lower height and occurred in the first 30 sec of salt stimulation. A third type with the lowest height appeared with those of the second type after prolonged stimulation with KCl. A fourth type with a high amplitude resulted from mechanical stimulation. The sensilla adapted to sugar solutions linearly to the logarithm of time and non-linearly to the log of salt concentrations. Glucose-fructose mixed-sugar solution effected synergism of response while sucrose solutions caused inhibition when mixed with glucose and/or fructose. Responses of the sensilla to mechanical stimulation showed phasic-tonic characteristics. None of the sensilla tested responded to water.     

STUDIES ON PERMEABILITY OF MEMBRANES : VII. CONDUCTIVITY OF ELECTROLYTES WITHIN THE MEMBRANE.

Two methods of measuring the electrical conductivity of the dried collodion membrane in contact with an electrolyte solution are described and the results of such measurements with different electrolytes in different ranges of concentration recorded. Some of the difficulties encountered in making these measurements are outlined. Of special interest was the fact that each membrane with each electrolyte showed a maximum level of resistance at a certain point in the dilution scale, a level which was not surpassed by further dilution. It is believed that this level was fixed by the collodion itself rather than by the contiguous electrolyte solution. Its existence limited the results available for reasonable interpretation. In relatively concentrated solutions the conductivity was shown to be approximately proportional to the concentration. With different electrolytes in the same concentration it was shown that the conductivities varied much more than in simple solutions without a membrane and that they fell in the order HCl > KCl > NaCl > LiCl. A method was described whereby the electrolyte content of a membrane in contact with different chloride solutions could be determined. It was shown that a membrane saturated with either 0.5 N HCl or 0.5 N KCl had practically the same total electrolyte content whereas the same membrane in contact with 0.5 N LiCl contained only half the quantity. These results were used in interpreting the conductivity data, the evidence presented strongly suggesting that two factors are operative in causing the widely divergent conductivities recorded with different electrolytes. The first factor depended on the quantity of electrolyte which can enter the membrane pores, a quantity dependent on the size of the pores and the volume of the larger of the two hydrated ions of the electrolyte. This factor was the chief one in determining the difference in conductivity between KCl and LiCl. The second factor was concerned with differences in the mobility of the various cations within the membrane brought about by friction between the moving ions and the pore walls. With KCl and HCl the quantity of electrolytes entering the membrane was in each case the same, being determined by the size of the larger Cl^- ion. The widely different conductivity values were explained as due to the changes in the mobility of the two cations within the membrane pores.     

Equilibrium studies of lecithin-cholesterol interactions I. Stoichiometry of lecithin-cholesterol complexes in bulk systems

The maximum molar ratio of lecithin:cholesterol in aqueous dispersions has been reported to be 2:1, 1:1, or 1:2. The source of the desparate results has been examined in this study by analyzing (a) the phase relations in anhydrous mixtures (from which most dispersions are prepared) and (b) various methods of preparing aqueous dispersions, with the purpose of avoiding the formation of metastable states that may be responsible for the variability of the lecithin-cholesterol stoichiometry. Temperature-composition phase diagrams for anhydrous mixtures of cholesterol (CHOL) with dimyristoyl (DML) and with dipalmitoyl (DPL) lecithin were obtained by differential scanning calorimetry (DSC). Complexes form with molar ratios for lecithin:CHOL of 2:1 and 1:2; they are stable up to 70°C. When x(CHOL) < 0.33, two phases coexist: complex (2:1) plus pure lecithin; when 0.33 < x(CHOL) < 0.67 complexes (2:1) and (1:2) coexist as separate phases. The corresponding phase diagram in water for these mixtures was determined by DSC and isopycnic centrifugation in D₂O-H₂O gradients. Aqueous dispersions were prepared by various methods (vortexing, dialysis, sonication) yielding identical results except as noted below. The data presented supports the following phase relations. When x(CHOL) < 0.33, two lipid phases coexist: pure lecithin plus complex (2:1) where the properties of the lecithin phase are determined by whether the temperature is below or above T_c, the gel-liquid crystal transition temperature. Therefore, complex (2:1) will coexist with gel state below T_c and with liquid crystal above T_c. The densities follow in the order gel > complex (2:1) > liquid crystal. The density of complex (2:1) is less sensitive to temperature in the range 5°-45°C compared to the temperature dependence for DML and DPL where large changes in density occur at T_c. When x(CHOL) > 0.33, CHOL phase coexists with complex (2:1); anhydrous complex (1:2) is apparently not stable in H₂O. The results are independent of the method and temperature used for preparing the lipid dispersions. However, when dispersions are prepared by sonication or with solvents at T > T_c, an apparent 1:1 complex is formed. Evidence suggests the 1:1 complex is metastable.     

Monovalent Ion Selectivity Sequences of the Rat Connexin43 Gap Junction Channel

The relative permeability sequences of the rat connexin 43 (rCx43) gap junction channel to seven cations and chloride were examined by double whole cell patch clamp recording of single gap junction channel currents in rCx43 transfected neuroblastoma 2A (N2A) cell pairs. The measured maximal single channel slope conductances (γ_j, in pS) of the junctional current-voltage relationships in 115 mM XCl were RbCl (103) ≥ CsCl (102) > KCl (97) > NaCl (79) ≥ LiCl (78) > TMACl (65) > TEACl (53) and for 115 mM KY were KBr (105) > KCl (97) > Kacetate (77) > Kglutamate (61). The single channel conductance-aqueous mobility relationships for the test cations and anions were linear. However, the predicted minimum anionic and cationic conductances of these plots did not accurately predict the rCx43 channel conductance in 115 mM KCl. Instead, the conductance of the rCx43 channel in 115 mM KCl was accurately predicted from cationic and anionic conductance-mobility plots by applying a mobility scaling factor D_x/D_o, which depends upon the relative radii of the permeant ions to an estimated pore radius. Relative permeabilities were determined for all of the monovalent cations and anions tested from asymmetric salt reversal potential measurements and the Goldman-Hodgkin-Katz voltage equation. These experiments estimate the relative chloride to potassium permeability to be 0.13. The relationship between the relative cation permeability and hydrated radius was modeled using the hydrodynamic equation assuming a pore radius of 6.3 ± 0.4 Å. Our data quantitatively demonstrate that the rCx43 gap junction channel is permeable to monovalent atomic and organic cations and anions and the relative permeability sequences are consistent with an Eisenman sequence II or I, respectively. These predictions about the rCx43 channel pore provide a useful basis for future investigations into the structural determinants of the conductance and permeability properties of the connexin channel pore.     

Release of Rhizobium spp. from Tropical Soils and Recovery for Immunofluorescence Enumeration

Limitations associated with immunofluorescence enumeration of bacteria in soil derive largely from the efficiency with which cells can be separated from soil particles and collected on membrane filters for staining. Many tropical soils fix added bacteria tightly, resulting in low recoveries. Eight soils, representative of three of the major soil orders found in the tropics (oxisols, vertisols, and inceptisols), were tested for recovery of added Rhizobium strains. All except one Hawaiian andept (Typic Eutrandept) yielded recoveries ranging from <1 to 13%. Recovery from the andept was 100%. In soil-sand mixtures, addition of only a small amount of soil caused a dramatic decrease in recovery of added rhizobia. Increasing the soil content of the mixture from 0% (10 g of sand) to 50% (5 g of soil-5 g of sand) reduced recoveries from >90 to <1%. Varying the ionic strength and pH of the extracting solution did not cause marked increases in recovery. Protein solutions, ethylenediaminetetraacetate, and NaHCO₃, on the other hand, improved release of bacteria. We report a modification to the usual membrane filter immunofluorescence procedure which yielded consistently high and reproducible recovery (coefficient of variation, 30%) of rhizobia from several tropical soils. In the modified procedure, partially hydrolyzed gelatin, diluted in ammonium phosphate, was used to suspend the soil. This caused dispersion of the soil and release of the bacteria from soil flocs. The efficiency of recovery of Rhizobium spp. from several tropical and two temperate soils remained high as the content of these soils in soil-sand mixtures was increased from 0 to 100%. The modified membrane filter immunofluorescence procedure was used to follow the growth of a strain of chickpea (Cicer arietinum) Rhizobium in a sterilized oxisol. The results showed a close agreement with viable counts at different stages during the growth cycle. Diluent for the hydrolyzed gelatin also had a marked effect on recovery. The efficiency of release of Rhizobium spp. from an oxisol was in the following order for the diluents used: 0.1 M (NH₄)₂HPO₄ > 0.1 M Na₂HPO₄ = 0.1 M sodium-phosphate-buffered saline (pH 7.2) > 0.2 M NH₄Cl > 0.2 KCl > NaCl = LiCl > water.     

A PERFUSING SOLUTION FOR THE LOBSTER (HOMARUS) HEART AND THE EFFECTS OF ITS CONSTITUENT IONS ON THE HEART

1. All inorganic perfusing solution for the heart of the lobster Homarus americanus, to allow prolonged normal beating (20 hours or more) must agree closely with the inorganic composition of the serum, which varies differentially with that of the environmental sea water. 2. All of the chief inorganic ions of the serum are necessary—Na, K, Ca, Mg, Cl, and SO₄; the critical numbers of the ions being 100, 3, 5, 2–3, 116, and 1–2 respectively. Absence of Mg and SO₄ will be tolerated for several hours. 3. The pH of the solution must agree with that of the serum within 0.2. 4. The osmotic pressure of the solution must agree with that of the serum within 15 per cent. 5. Beating of the heart will continue for several hours on improperly balanced solutions but changes in frequency, tone, or amplitude will occur. Hearts adapted to such solutions will show different responses to physical and chemical stimuli of the solution than those perfused on properly balanced solutions. 6. Arrest in systole is caused by isotonic NaCl, KCl, LiCl, and urea, and arrest in diastole by isotonic CaCl₂, MgCl₂, NaBr, NaI, MgSO₄, and glucose. 7. Lithium cannot replace sodium; neither can bromide or iodide replace chloride ions.     

A comparison and optimization of methods and factors affecting the transformation of Escherichia coli

DNA manipulation routinely requires competent bacteria that can be made using one of numerous methods. To determine the best methods, we compared four commonly used chemical methods (DMSO, MgCl₂–CaCl₂, CaCl₂ and Hanahan''s methods) on frequently used Escherichia coli (E. coli) strains: DH5α, XL-1 Blue, SCS110, JM109, TOP10 and BL21-(DE3)-PLysS. Hanahan''s method was found to be most effective for DH5α, XL-1 Blue and JM109 strains (P<0.05), whilst the CaCl₂ method was best for SCS110, TOP10 and BL21 strains (P<0.05). The use of SOB (super optimal broth) over LB [Luria–Bertani (broth)] growth media was found to enhance the competency of XL-1 Blue (P<0.05), dampened JM109′s competency (P<0.05), and had no effect on the other strains (P>0.05). We found no significant differences between using 45 or 90 s heat shock across all the six strains (P>0.05). Through further optimization by means of concentrating the aliquots, we were able to get further increases in transformation efficiencies. Based on the optimized parameters and methods, these common laboratory E. coli strains attained high levels of TrE (transformation efficiency), thus facilitating the production of highly efficient and cost-effective competent bacteria.     

Using KCl to determine size at competence for larvae of the marine gastropod Crepidula fornicata (L.)

Competent larvae of the marine gastropod Crepidula fornicata (L.) were induced to metamorphose (i.e., lose the velum) by elevating sea-water [KCl] by 5–50 mM. The response was optimal at 15–20-mM elevations, at which 50% metamorphosis was obtained in <4 h. Larvae that did not metamorphose during brief exposures (1–5 h) to elevated [KCl] generally maintained the larval form following transfer to control sea water, suggesting that competent larvae must be continuously immersed in the test solutions for metamorphosis to occur. The smallest larvae to respond to elevated [KCl] had shell lengths of ≈700–800 μm, the range of shell lengths within which larvae of this species become responsive to natural inducers. All larvae >≈1125 μm shell length metamorphosed in response to increased [KCl]. Rearing temperature may affect the size at which larvae of this species become responsive to K⁺. CaCl₂ (20-mM concentration elevations), GABA (4×10⁻⁷, 4×10⁻⁶ M), and NaCl (10–20-mM concentration elevations) generally failed to trigger metamorphosis. Twenty-mM elevations of [RbCl] and [CsCl] induced 100% metamorphosis but the juveniles were immobile and died after several days. Elevating [KCl] appears to be a reliable way to assess competence and trigger metamorphosis in larvae of C. fornicata.     

Molecular Mechanism of the Synergistic Effects of Vitrification Solutions on the Stability of Phospholipid Bilayers

The vitrification solutions used in the cryopreservation of biological samples aim to minimize the deleterious formation of ice by dehydrating cells and promoting the formation of the glassy state of water. They contain a mixture of different cryoprotective agents (CPAs) in water, typically polyhydroxylated alcohols and/or dimethyl sulfoxide (DMSO), which can damage cell membranes. Molecular dynamics simulations have been used to investigate the behavior of pure DPPC, pure DOPC, and mixed DOPC-β-sitosterol bilayers solvated in a vitrification solution containing glycerol, ethylene glycol, and DMSO at concentrations that approximate the widely used plant vitrification solution 2. As in the case of solutions containing a single CPA, the vitrification solution causes the bilayer to thin and become disordered, and pores form in the case of some bilayers. Importantly, the degree of thinning is, however, substantially reduced compared to solutions of DMSO containing the same total CPA concentration. The reduction in the damage done to the bilayers is a result of the ability of the polyhydroxylated species (especially glycerol) to form hydrogen bonds to the lipid and sterol molecules of the bilayer. A decrease in the amount of DMSO in the vitrification solution with a corresponding increase in the amount of glycerol or ethylene glycol diminishes further its damaging effect due to increased hydrogen bonding of the polyol species to the bilayer headgroups. These findings rationalize, to our knowledge for the first time, the synergistic effects of combining different CPAs, and form the basis for the optimization of vitrification solutions.     

Effect of agents affecting water structure on the uptake of saccharides by agar and polyacrylamide gels

Uptake of D -xylose, D -glucose, lactose, and dextran 10 was studied in 3% and 12.5% polyacrylamide gels in the presence of 2 M LiCl, 2 M NaCl, 2 M KCl, 2 M RbCl, 2 M CsCl, 2 M MgCl₂, 2 M CaCl₂, 1 M NaF, 1 M NaI, 0.5 M guanidine thiocyanate, 0.5 M guanidine sulphate, and 0.5 M N,N′-diethylurea. With the exception of N,N′-diethylurea and, in some cases, LiCl, which had an accelerating effect, the compounds retarded considerably the uptake of saccharides by agar gel but had only a slight effect in polyacrylamide. The nature of the gel is thus of primary importance in interactions of this type. According to the magnitude of their effect on saccharide uptake, the salts used were arranged into several series. An attempt was made to correlate the effects of individual salts with their hydration properties. The strongest effect was found to be exerted by KCl, RbCl, and CsCl, i.e., by chlorides of cations possessing negative hydration shells.     

ELECTROKINETICS : XVII. SURFACE CHARGE AND ION ANTAGONISM

1. The question of the critical pore diameter for streaming potential is discussed. 2. The surface charge is calculated for cellulose in contact with solutions of K₃PO₄, K₂CO₃, K₂SO₄, KCl, and ThCl₄. 3. The surface charge of cellulose in contact with a solution of 2 x 10^–4 N NaCl is calculated as a function of temperature and is found to show a sharp break at 39°. This is interpreted in terms of the change of the specific heat of water. 4. A marked ion antagonism is found in NaCl:KCl, KCl:MgCl₂, NaCl:MgCl₂, NaCl:CaCl₂, KCl:CaCl₂, CaCl₂:MgCl₂ mixtures when the surface charge is calculated as a function of concentration.     

Nanoscale Measurement of the Dielectric Constant of Supported Lipid Bilayers in Aqueous Solutions with Electrostatic Force Microscopy

We present what is, to our knowledge, the first experimental demonstration of dielectric constant measurement and quantification of supported lipid bilayers in electrolyte solutions with nanoscale spatial resolution. The dielectric constant was quantitatively reconstructed with finite element calculations by combining thickness information and local polarization forces which were measured using an electrostatic force microscope adapted to work in a liquid environment. Measurements of submicrometric dipalmitoylphosphatidylcholine lipid bilayer patches gave dielectric constants of ε_r ∼ 3, which are higher than the values typically reported for the hydrophobic part of lipid membranes (ε_r ∼ 2) and suggest a large contribution of the polar headgroup region to the dielectric response of the lipid bilayer. This work opens apparently new possibilities in the study of biomembrane electrostatics and other bioelectric phenomena.     

The effects of cholesterol inclusion on the molecular organisation of bimolecular lipid membranes

Dielectric measurements on planar egg phosphatidylcholine bilayers formed from n-hexadecane solutions indicate that these bilayers contain very low equilibrium concentrations of alkane. In 100 mM KCl the capacitance of the hydrophobic region was found to be 7.0 ±0.2 mF/m². The addition of cholesterol (at 2:1 mole ratio) was found to affect only marginally the capacitance of the hydrophobic region of such bilayers. Precise measurements of the frequency dependence of the bilayer impedance at very low frequencies now allow the resolution of several electrically distinct substructural regions within the bilayer. Examination of the effects of cholesterol inclusion upon the electrical parameters of these substructural regions indicate that cholesterol spans the acetyl region (i.e. the region containing the glycerol bridge of the phosphatidylcholine molecules in the bilayer) with the hydroxyl group of the cholesterol molecules located inbetween the phosphate group and the glycerol oxygens of the phosphatidylcholine molecules. The capacitance of the hydrophobic region of both phosphatidylcholine and phosphatidylcholine/cholesterol bilayers formed from n-hexadecane solutions was found to decrease slightly as the external KCl concentration was decreased.     

Structural changes in lecithin-water systems thermal-turbidimetric studies

Turbidity measurements were made of dilute aqueous dispersions of 1,2-dipalmitoyl-l-lecithin as the temperature was varied. In the range from 24 to 33° a decrease in turbidity is associated with the penetration of water between the layers of lipid in the crystalline structure. At the transition to the liquid crystalline form (39–41°) a sharp decrease in turbidity occurs. In solutions of 0.06 M LiCl, 1 mM CaCl₂, MgCl₂ or 0.05 M PO₄³ an increase in turbidity resulted at the transition temperature, whereas in 0.1 M NaCl, or quarternary ammonium salts the turbidity decreased. The presence of small amounts of dicetylphosphoric acid mixed with the lecithin decreased the turbidity, and at elevated pH levels there was no change at the transition temperature.     

THE EFFECT OF CERTAIN ELECTROLYTES AND NON-ELECTROLYTES ON PERMEABILITY OF LIVING CELLS TO WATER

1. Permeability to water in unfertilized eggs of the sea urchin, Arbacia punctulata, is found to be greater in hypotonic solutions of dextrose, saccharose and glycocoll than in sea water of the same osmotic pressure. 2. The addition to dextrose solution of small amounts of CaCl₂ or MgCl₂ restores the permeability approximately to the value obtained in sea water. 3. This effect of CaCl₂ and MgCl₂ is antagonized by the further addition of NaCl or KCl. 4. It is concluded that the NaCl and KCl tend to increase the permeability of the cell to water, CaCl₂ and MgCl₂ to decrease it. 5. The method here employed can be used for quantitative study of salt antagonism.     

Elastic Torques about Membrane Edges: A Study of Pierced Egg Lecithin Vesicles

The shape of mechanically pierced giant vesicles is studied to obtain the elastic modulus of Gaussian curvature of egg lecithin bilayers. It is argued that such experiments are governed by an apparent modulus, ¯κ_app, not the true modulus of Gaussian curvature, ¯κ. A theory of ¯κ_app is proposed, regarding the pierced bilayer vesicle as a closed monolayer vesicle. The quantity measured, i.e. ¯κ_app/κ, where κ is the rigidity, agrees satisfactorily with the theory. We find ¯κ_app = -(1.9 ± 0.3) · 10^-12 erg (on the basis of κ = (2.3 ± 0.3) · 10^-12 erg). The result may have implications for bilayer fusion.