CONDUCTIVITY AS A MEASURE OF THE PERMEABILITY OF SUSPENDED CELLS

The problem of determining by means of measurements of electrolytic conductance the permeability of living cells in suspension is considered in some detail and it is pointed out that several factors, usually neglected, have an important influence on the interpretation of such studies. These are: 1. The relative volume and the shape of cells, which are responsive to changes in osmotic pressure and constitution of the surrounding solution. The sources of error in various methods of determining the true volume of red blood cells in a suspension are explained. The hematocrit method appears to be the most reliable method in this case. 2. The proportion of living cells, which is especially to be regarded in the case of suspensions of bacteria. It is shown that this may be very high when appropriate cultural methods are used. The conductance of the dead cells must also be taken into account. 3. The progressive nature of the changes occurring during the course of an experiment. Approximate accuracy may be obtained by proper interpolation. 4. The conductivity of the protoplasm itself, which varies in response to variations is that of the surrounding fluid. It is emphasized that cells, and in particular red blood cells, are not to be regarded as stable non-conducting particles, but rather as labile and as permeable to electrolytes. It is shown that the available data support this interpretation.     

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.     

DIRECT AND INDIRECT DETERMINATIONS OF PERMEABILITY

1. Methods are described for obtaining cell sap from Nitella without contamination. 2. Tests of the cell sap show that in a balanced solution of NaNO₃ plus Ca(NO₃)₂ there is a slow penetration of NO₃ and that the cell remains in a normal condition, but in pure NaNO₃ there is rapid penetration accompanied by injury. 3. Inasmuch as determinations of electrical conductivity give the same result it may be concluded that this method gives reliable information regarding permeability. 4. While observations on recovery from plasmolysis give similar results, the method is less satisfactory.     

ULTRASTRUCTURE AND PERMEABILITY OF NUCLEAR MEMBRANES

The fine structures of nuclear envelopes known to have different permeability properties were compared. Membranes of salivary gland cell nuclei of Drosophila (third instar) and Chironomus (prepupae), which are strong barriers to ion diffusion, and membranes of oocyte nuclei (germinal vesicle) of Xenopus and Triturus, which are much more ion-permeable, show no essential difference in size, frequency, and distribution of their membrane gaps ("pores") which could account for the marked disparities in membrane permeability. The gaps are occupied by diffuse electron-opaque material with occasional central regions of strong opacity. This material may possibly account for the high diffusion resistance of Drosophila and Chironomus nuclear envelopes, where the resistance is far too great to allow free diffusion through the gaps. But material of this kind is also present in the more permeable nuclear envelopes of Xenopus and Triturus oocytes, and there are no convincing structural differences discernible with the techniques employed.     

EXOSMOSIS IN RELATION TO INJURY AND PERMEABILITY

The time curve expressing the increase in the permeability of Nitella during the progress of death is practically the same whether derived from measurements of exosmosis or of electrical resistance.     

CONDUCTIVITY AS A MEASURE OF VITALITY AND DEATH

The conductance of Laminaria, Saccharomyces, Bacillus coli and Bacillus butyricus, Chlorella, and of red blood cells has been studied by the writer''s method, and Laminaria by that of Osterhout. For the material studied it has been found that: 1. The conductance of living tissue is closely proportionate to, and determined by that of the surrounding fluid with which it is apparently in equilibrium. Changes in the conductance of the fluid are quickly followed by compensatory changes in that of the tissue. 2. A quantity is defined which is independent of the conductivity of the fluid bathing the tissues. This is called the "net conductance." 3. All the tissues studied, even when dead, offer a resistance to the passage of current greater than that of the surrounding solution. Exceptions which occur under certain conditions will be discussed in a later paper. 4. In view of the wide variety of material studied it seems admissible, in the absence of any evidence to the contrary, to suppose that these conclusions are generally applicable.     

EFFECTS OF HELMINTHOSPORIUM VICTORIAE AND VICTORIN UPON PERMEABILITY

Wheeler, Harry, and Homer S. Black. (Louisiana State U., Baton Rouge.) Effects of Helminthosporium victoriae and victorin upon permeability. Amer. Jour. Bot. 50(7): 686–693. Illus. 1963.—Helminthosporium victoriae, the causal agent of Victoria blight of oats, produces a potent toxin called victorin. All of the symptoms of Victoria blight, both visible and biochemical, can be induced in susceptible plants either by infection with H. victoriae or by treatment with victorin. Among the effects produced both by the fungus and the toxin are marked changes in respiration and cell permeability. These are of special interest because they are characteristic of many plant diseases. This paper is concerned with the nature of changes in permeability and the possible relation of these to changes in respiration observed in tissues infected with H. victoriae or treated with victorin. Suseeptible oat tissues treated with victorin lost electrolyes when suspended and shaken in distilled water more rapidly than control tissues, and the magnitude of the effect varied with the concentration of victorin applied. Similar results were obtained with naturally infected susceptible plants but not with inoculated or victorin-treated resistant plants. The rate of electrolyte loss from victorin-treated tissue had a low temperature coefficient typical of a physical process and was not dependent upon oxygen tension. The concentration of victorin needed to produce an increase in the rate of electrolyte loss was approximately 50-fold less than that required to induce a significant increase in the respiratory rate. Changes in permeability were detected within 5 min after victorin was applied, whereas respiratory changes were not clearlyevident until after 30 min. These results indicate that if a causal relationship between these 2 phenomena exists, changes in permeability are responsible for changes in respiratory activity rather than vice versa.     

ACCUMULATION OF SALT AND PERMEABILITY IN PLANT CELLS

1. Comparisons are made of concentrations of K and Br in exudates of barley roots and in expressed sap from roots, under conditions favorable for aerobic metabolism. Both methods lead to the same general viewpoint concerning metabolically governed transport of solutes by living plant cells. 2. Cyanide in low concentration prevented salt accumulation by barley roots. Methylene blue, without decrease of CO₂ production by roots, destroyed power of salt accumulation. 3. K and Br ions entered roots to only a slight extent under an anaerobic condition, even with an inward gradient of ionic concentration. 4. Lactate or alcohol, under aerobic conditions, did not prevent rapid accumulation of salt by root cells. 5. Experiments on fluids obtained by suction from tomato roots gave evidence of loss of salt-accumulating power under the influence of N₂ gas or CO₂ gas, together with probable effects on cell permeability. 6. Several experiments on Nitella cells in which radioactive isotopes were used are reported. Bromide gradually moved into vacuolar sap until the concentration appeared to exceed that of the protoplasm, on the basis of the results of the several types of experiments. Accumulation of salt in the vacuole did not occur anaerobically. 7. Some views of interrelations of permeability, salt accumulation, and metabolism are suggested for further discussion.     

森林降水酸度及电导率的时空变化

在离大气污染源距离不同的两片杉木(Cunninghamia lanceolata)人工林中建立监测场,对降水化学进行了为期3年(1994～1996)的定位监测。降水通过林冠截留后,其酸度和电导率均明显增加,尤以树干径流为显著。在 FFC监测场,降雨、穿透雨和树干径流雨量加权平均pH值分别为6.13、6.06和4.18,在XQF监测场,其相应的数值分别为5.86、5.67和3.37;降雨和穿透雨的酸度表现出一定的季节变化动态,其最低月均pH值出现在夏委,最高值在冬季。在FFC监测场,降雨、穿透雨和树干径流雨量加权平均EC值分别为28.51μs·cm-1、63.71μs·cm-1、240.85μs·cm-1,在XQF监测场,其相应的数值分别为36.99μs·cm-1、66.41μs·cm-1、501.85μs·cm-1：降水电导率表现出显著一致的季节变化格局,其月均值均以夏季最低,冬季最高,春秋季居中,这种格局强烈受降雨量的影响。离污染源较近的XQF监测场,降水酸度和电导率明显高于相对未受污染的FFC监测场。     

电导法研究表面活性剂与蛋白质的相互作用

较系统地研究了溶液中离子型表面活性剂与蛋白质相互作用时电导率的变化,并根据实验现象得出表面活性剂与蛋白质作用的两种模式－ 疏水作用模式和电荷作用模式。表面活性剂采用疏水作用模式与蛋白质结合时,蛋白质的二硫键逐一断裂,三级结构逐渐打开,电导率曲线出现一些小“平台”;采用电荷作用模式吸附蛋白质时,首先形成疏水复合体,产生白色浑浊,随离子型表面活性剂浓度的增加,疏水复合体转变成亲水复合体,白色浑浊完全溶解。在有的体系中,两种作用并不是界限分明,它们可以同时表现出来。并将实验结果做为研究蛋白质所引起的乳化及破乳机理的依据     

A COMPARISON OF PERMEABILITY IN PLANT AND ANIMAL CELLS

Quantitative studies show a striking agreement between frog skin and plant tissues in respect to certain important aspects of permeability, antagonism, injury, recovery, and death.