Studies on the mechanism by which cyanine dyes measure membrane potential in red blood cells and phosphatidylcholine vesicles.

A number of compounds related to TEA(+) (tetraethylammoniumion) were injected into squid axons and their effects on g(K) (the potassium conductance) were determined. In most of these ions a quaternary nitrogen is surrounded by three ethyl groups and a fourth group that is very hydrophobic. Several of the ions cause inactivation of g(K), a type of ionic gating that is not normally seen in squid axon; i.e., after depolarization g(K) increases and then spontaneously decreases to a small fraction of its peak value even though the depolarization is maintained. Observations on the mechanism of this gating show that (a) QA (quaternary ammonium) ions only enter K(+) channels that have open activation gates (the normal permeability gates). (b) The activation gates of QA-occluded channels do not close readily. (c) Hyperpolarization helps to clear QA ions from the channels. (d) Raising the external K(+) concentration also helps to clear QA ions from the channels. Observations (c) and (d) strongly suggest that K(+) ions traverse the membrane by way of pores, and they cannot be explained by the usual type of carrier model. The data suggest that a K(+) pore has two distinct parts: a wide inner mouth that can accept a hydrated K(+) ion or a TEA(+)-like ion, and a narrower portion that can accept a dehydrated or partially dehydrated K(+) ion, but not TEA(+).

/pdf/interaction-of-tetraethylammonium-ion-derivatives-with-the-4wfk9dvb2u.pdf

Interaction of tetraethylammonium ion derivatives with the potassium channels of giant axons.

I Basics- 1 The Physical Nature of Planar Bilayer Membranes- 2 Ion Channel Electrostatics and the Shapes of Channel Proteins- 3 Superoxide Dismutase as a Model Ion Channel- 4 Single-Channel Enzymology- 5 How to Set Up a Bilayer System- 6 Fusion of Liposomes to Planar Bilayers- 7 Incorporation of Ion Channels by Fusion- II Nicotinic Acetylcholine Receptor- 8 The Reconstituted Acetylcholine Receptor- 9 Immunologic Analysis of the Acetylcholine Receptor- 10 Function of Acetylcholine Receptors in Reconstituted Liposomes- III Sodium Channel- 11 Skeletal Muscle Sodium Channels: Isolation and Reconstitution- 12 Reconstitution of the Sodium Channel from Electrophorus electricus- 13 The Reconstituted Sodium Channel from Brain- 14 Gating of Batrachotoxin-Activated Sodium Channels in Lipid Bilayers- 15 Ion Conduction Through Sodium Channels in Planar Lipid Bilayers- 16 Blocking Pharmacology of Batrachotoxin-Activated Sodium Channels- IV Other Channels in Model Membranes- 17 The Large Calcium-Activated Potassium Channel- 18 The Sarcoplasmic Reticulum Potassium Channel: Lipid Effects- 19 Characterization of Dihydropyridine-Sensitive Calcium Channels from Purified Skeletal Muscle Transverse Tubules- 20 Calcium Channels- 21 Phosphorylation of a Reconstituted Potassium Channel- 22 Voltage Gating in VDAC: Toward a Molecular Mechanism- 23 Analysis and Chemical Modification of Bacterial Porins

Ion Channel Reconstitution

The cristae membrane or M phase of resting or respiring rat liver mitochondria becomes relatively permeable to K+ ions in presence of valinomycin. The equilibrium distribution of K+ ions across the membrane can therefore be used to estimate the membrane potential ΔΨ provided that precautions are taken to minimise swelling of the valinomycin-treated mitochondria. The pH difference ΔpH across the M phase of anaerobic mitochondria has been estimated from the buffering powers of the inner and outer phases and from the change of pH observed on lysing the mitochondria with Triton X-100. When the anaerobic mitochondria (State 5), in presence of β-hydroxybutyrate, are brought to a state of steady respiration either in absence (State 4) or in presence (State 3) of phosphate acceptor, the changes of pH and of pK of the medium recorded with H+ ion-sensitive and K+ ion-sensitive electrodes can be used to estimate the changes of ΔΨ and ΔpH across the M phase. The absolute values of ΔΨ and ΔpH have been estimated from the values determined in State 5 and the change of these values in the transition from State 5 to States 4 and 3.



The total protonmotive force Δp =ΔΨ– 59 ΔpH across the M phase of the mitochondria oxidising β-hydroxybutyrate in State 4 at 25° in a 250 mM sucrose medium near pH 7 is estimated to be about 230 mV, of which the major component is ΔΨ when the effect of translocation of K+ ions across the M phase is minimised. Under conditions permitting accumulation of a relatively large quantity of cation (State 6), Δp is not significantly different from that in State 4, but the major component is −ZΔpH.



The effects of changing Δp in mitochondrial suspensions in State 4 with uncoupling agent and with pulses of acid, alkali, calcium salt and ADP have been found to be in accord with the chemiosmotic hypothesis. In particular Δp in State 3 (ADP and Pi present) is estimated to be about 30 mV less than in State 4.

Estimation of membrane potential and pH difference across the cristae membrane of rat liver mitochondria.

Membrane models with phospholipids.

Optically black membranes prepared from sheep red cell lipids have a high electrical resistance (1–3 x 108 ohm-cm2). The ionic transference numbers (Ti) for cations (Na+ or K+) are equal to each other but at least four to five times greater than for Cl-. The cyclic depsipeptide valinomycin produces a striking decrease in the membrane resistance when K+, but not when Na+ is in the solutions bathing the membrane. The ratio TNa/TK, estimated from membrane voltages in the presence of ionic concentration gradients, approaches zero. The order of membrane monovalent cation selectivity, in the presence of valinomycin, is H+ > Rb+ > K+ > Cs+ > Na+. Addition of the antibiotic to one side of a membrane which separates identical solutions of NaCl produces a substantial (up to 80 mV) membrane voltage (side opposite valinomycin negative). These data are consistent with the hypothesis that valinomycin can interact with appropriately sized cations (hydrated diameter ??? 6 A) to increase their membrane permeability, perhaps by forming hydrogen bonds between the solvation shell of the cations and carbonyl oxygens in the valinomycin molecule which are directed toward the aperture of the ring.

https://rupress.org/jgp/article-pdf/50/11/2527/1243640/2527.pdf

The effect of valinomycin on the ionic permeability of thin lipid membranes.

For some years, work in this laboratory has been directed toward elucidation of the mechanism of selectivity of high-potassium (HK) and low-potassium (LK) sheep red cell membranes for Na + and K + (I-4). One recent approach has been to compare the ionic permeability of the intact ceil membranes with thin artificial bilayer membranes prepared from lipids extracted from these cells (5). It was found that the thin lipid membranes have ionic permeability properties which are vastly different from those of intact HK and LK sheep red cell membranes. For example, the PC electrical resistance of the bilayers is about 2 X 10 s ohm cm 2, while that of the red cell membranes is estimated to be from 10 to 100 ohm cm 2. Furthermore, the bilayers are more permeable to both Na + and K + than they are to Cl-, while the ratio of Clto K + or Na + permeability of red cells is of the order of 106 (6). Finally, the thin lipid membranes do not distinguish between Na + and K +, and the ionic transport properties of such membranes prepared from HE and LK sheep red cell lipids are identical. The intact cell membranes do distinguish between these alkali metal ions, and, furthermore, the Na + and K + transport properties of the two genetic types of sheep red cells are significantly different. Apparently, the thin lipid membranes lack essential components which are responsible for the distinctive cation permeability properties of the intact cell membranes. In the course of continuing attempts to identify such components, we became aware of reports of the effect of the macrocyclic depsipeptide antibiotic, valinomycin, on the ionic permeabil i ty of lecithin (7) and mixed brain lipid (8) bilayer membranes. This compound had previously been reported to stimulate the respiration of mitochondria in the presence of K + but not in the presence of Na + (9). Valinomycin was found to produce specific permeabili ty of intact H K and L K sheep red cell membranes, as well as thin artificial membranes prepared from lipids extracted from these cells, to K + but not to Na + ( 10, 11). In the presence of K + ( 10 t M) and valinomycin (5 X 10 -~ M), the electrical resistance of the lipid bilayer membranes is about 103 ohm cm ~, which is in the range of biological membranes. The significance of these observations derives from the unusual structure of valino-

/pdf/the-effects-of-macrocyclic-compounds-on-cation-transport-in-12rsuvhttz.pdf

The effects of macrocyclic compounds on cation transport in sheep red cells and thin and thick lipid membranes.

A cyclic depsipeptide antibiotic, valinomycin, was found to produce increased selective permeability of the plasma membranes of HK and LK sheep red blood cells to potassium but not to sodium ions. The compound had relatively little effect on the active extrusion of sodium from HK sheep red blood cells or on the Na + K-stimulated ATPase activity of membranes derived from these cells. It is proposed that the selective cation permeability produced by this compound depends primarily on steric factors, particularly the relationship between the diameter of the ring and the effective diameter of the ion. The significance of these results for the problem of the mechanism of ionic selectivity in natural membranes is discussed.

/pdf/the-effect-of-valinomycin-on-potassium-and-sodium-5dnqo2lq9k.pdf

The Effect of Valinomycin on Potassium and Sodium Permeability of HK and LK Sheep Red Cells

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The effect of valinomycin on the ionic permeability of thin lipid membranes.

The effects of macrocyclic compounds on cation transport in sheep red cells and thin and thick lipid membranes.

The Effect of Valinomycin on Potassium and Sodium Permeability of HK and LK Sheep Red Cells