The influence of gramicidin A and valinomycin of the permeability of mammalian erythrocytes.

1. The K+ transport in erythrocytes induced by gramicidin A or valinomycin is a first-order reaction. The activation energy of the induced transport is low and amounts to 6 and 10 kcal/mole, respectively. The indirect method for calculation of the driving force of diffusion, c, is given; in pig erythrocytes the c value for gramicidin A is 21.7, and for valinomycin 35.4 mM-KCl. 2. The valinomycin-induced transport was found to be the same in erythrocytes and biomolecular lipid membranes. The gramicidin A-induced transport corresponds to that of a single gramicidin channel, and not to the multichannel transport observed in the model systems. 3. Erythrocytes of various mammals show large differences in sensitivity to the ionophores. No correlation could be found between membrane lipids and the induced permeability. The role of membrane proteins in ionophore-induced permeability is discussed.     

The permeability of liposomes to nonelectrolytes

The Journal of Membrane Biology - The effect of temperature on the permeability of nonelectrolytes across liposomal membranes above and below their transition temperature has been studied by using...     

The permeability of the frog choroid plexus to nonelectrolytes

Summary Anin vitro preparation of the frog choroid plexus has been used to measure the permeability of the choroidal epithelium to 50 nonelectrolytes by an osmotic method. The method involves the measurement of nonelectrolyte reflection coefficients () by a rapid electrical procedure. For the majority of compounds tested, there was a good correlation between the rate of solute permeation and the solute's bulk-phase lipid: water partition coefficients; i.e., the higher the partition coefficient the greater the permeability. The membrane lipids of the choroid plexus differ from the membrane lipids of the gall bladder in at least three ways: (1) the lipids of the choroid plexus cannot distinguish between branched chain solutes and their straight chain isomers; (2) small polar solutes such as urea and acetamide permeate via the membrane lipids to a significant extent; and (3) the smaller selectivity ratios suggest that the lipids of the choroid plexus contain more hydrogen bonding sites (i.e., there are stronger solute: lipid intermolecular forces in the choroid plexus). The permeability characteristics of the choroid plexus are qualitatively similar to those of most other cell membranes. In addition, there is evidence for the presence of a special mechanism for the transport of sugar across this epithelium.     

The effect of amphotericin B on the permeability of lipid bilayers to divalent trace metals

In this study amphotericin B released the divalent trace metals Zn²⁺, Co²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺, Cd²⁺ and Pb²⁺ from multilamellar liposomes containing cholesterol. This observation is consistent with amphotericin B channels being permeable to these metals, and it is proposed, therefore, that the antibiotic may be useful in investigating the metabolism of these elements.     

The temperature dependence of passive potassium permeability in mammalian erythrocytes

The effect of temperature on the "passive" permeability of mammalian plasma membranes to K+, measured as the residual flux in the presence of ouabain and bumetanide, was investigated in erythrocytes of several species. Without Ca2+ in the medium, only human red cells demonstrated the "paradoxical" rise in passive flux at low temperature (i.e., below 12 degrees C) seen by other workers. In the other species no such effect was apparent; K+ influx decreased progressively with cooling down to 0 degree C. Below 18.5 degrees C the apparent energy of activation (Ea) was very low--close to that for free diffusion in water--for red cells of all species except human. Above 18.5 degrees C the Ea was much greater and was also more variable amongst the red cells of the species chosen. Neither the inhibitors used nor cell volume changes during incubation accounted for the absence of the paradoxical effect in the species studied here. A rise in permeation of K+ with cooling can, however, be produced by the addition of Ca2+ to the medium, probably by activation of the Ca2+-sensitive K+ channel. This effect would account for previous reports of a paradoxical effect in dog and rat erythrocytes.     

Alteration of membrane permeability by amphotericin B

Amphotericin B (AmB) increased unidirectional Na transport and net transcellular sodium movements across the skin of the frog, Rana pipiens, when added to the solution bathing the corium side, but not from the outer epidermal surface. The AmB response was prevented with pretreatment with amiloride, ouabain and mucosal sodium substitution. Alteration in pH markedly reduced the permeability changes induced by AmB. AmB did not interfere with the increase in sodium transport induced by antidiuretic hormone. The present study demonstrates that AmB interacts with the skin of the frog, Rana pipiens, from the corium side specifically increasing transepithelial sodium transport. The increase in transport apparently occurs through the existing sodium pathway.     

Permeability of the squid giant axon to organic cations and small nonelectrolytes

Summary The permeability of the Na channel of squid giant axon to organic cations and small nonelectrolytes was studied. The compounds tested were guanidinium, formamidinium, and¹⁴C-labeled urea, formamide, thiourea, and acetone. Permeability was calculated from measurements of reversal potential and influx on internally perfused, voltage clamped squid axons. The project had two objectives: (1) to determine whether different methods of measuring the permeability of organic cations yield similar values and (2) to see whether neutral analogs of the organic cations can permeate the Na channel. Our results show that the permeability ratio of sodium to a test ion depends upon the ionic composition of the solution used. This finding is consistent with the view put forward previously that the Na channel can contain more than one ion at a time. In addition, we found that the uncharged analogs of permeant cations are not measurably permeant through the Na channel, but instead probably pass through the lipid bilayer.     

The effect of amphotericin B on the water and nonelectrolyte permeability of thin lipid membranes

This paper reports the effects of amphotericin B, a polyene antibiotic, on the water and nonelectrolyte permeability of optically black, thin lipid membranes formed from sheep red blood cell lipids dissolved in decane. The permeability coefficients for the diffusion of water and nonelectrolytes (P_DDi) were estimated from unidirectional tracer fluxes when net water flow (J_w) was zero. Alternatively, an osmotic water permeability coefficient (P_f) was computed from J_w when the two aqueous phases contained unequal solute concentrations. In the absence of amphotericin B, when the membrane solutions contained equimolar amounts of cholesterol and phospholipid, P_f was 22.9 ± 4.6 µsec^-1 and P _DDHDH2O was 10.8 ± 2.4 µsec^-1. Furthermore, P_DDi was < 0.05 µsec^-1 for urea, glycerol, ribose, arabinose, glucose, and sucrose, and σ_i, the reflection coefficient of each of these solutes was one. When amphotericin B (10^-6 M) was present in the aqueous phases and the membrane solutions contained equimolar amounts of cholesterol and phospholipid, P _DDHDH2O was 18.1 ± 2.4 µsec^-1; P_f was 549 ± 143 µsec^-1 when glucose, sucrose, and raffinose were the aqueous solutes. Concomitantly, P_DDi varied inversely, and σ_i directly, with the effective hydrodynamic radii of the solutes tested. These polyene-dependent phenomena required the presence of cholesterol in the membrane solutions. These data were analyzed in terms of restricted diffusion and filtration through uniform right circular cylinders, and were compatible with the hypothesis that the interactions of amphotericin B with membrane-bound cholesterol result in the formation of pores whose equivalent radii are in the range 7 to 10.5 A.     

Changes of membrane permeability due to extensive cholesterol depletion in mammalian erythrocytes

55% of the total membrane cholesterol could be removed from porcine, bovine and human erythrocytes by incubating the cells in suspensions of lecithin liposomes. Up to 30% depletion, membrane permeability remained unaltered; more extensive depletion induced a marked increase of the transfer rates of nonelectrolytes and of organic acids penetrating by nonionic diffusion. This biphasic response of permeability to cholesterol depletion, which has not been observed in artificial lipid membranes, may be related to the heterogeneity of the erythrocyte membrane lipids or to a pool of cholesterol not interacting with the phospholipids.     

Changes in erythrocyte permeability due to palytoxin as compared to amphotericin B

Palytoxin causes within minutes a temperature-dependent K+ loss from human and rat erythrocytes which is followed within hours by haemolysis. It decreases the osmotic resistance in a concentration-dependent manner, so that osmotic influences are negligible for K+ release but considerable in haemolysis. External K+ inhibits the haemoglobin release and Rb+ inhibits the release of K+ and haemoglobin. Ca2+ (over 20 microM) and borate (over 5 microM) enhance the loss of K+ and haemoglobin. With both Ca2+ and borate present, the efficacy of palytoxin is raised about 10 000-fold. Under these conditions, about 15 palytoxin molecules per human cell trigger a 50% K+ loss over a wide range of cell concentrations. The palytoxin effect is reversible. After depletion from K+ by low concentrations of palytoxin, human cells can be refilled with K+ and resealed. The pores formed by palytoxin are small. They allow the entrance of Na+ and choline, whereas inositol is largely excluded and Ca2+, as well as sucrose and inulin, are completely excluded. Amphotericin B resembles palytoxin in its ability to cause a considerable prelytic K+ loss and to form small pores. However, it is about 1000-times weaker than palytoxin, is not inhibited by K+ or Rb+, is not activated by Ca2+ or borate, and has a negative temperature dependence. Thus palytoxin represents a novel type of cytolysin.