Redistribution of the electric field within the pore contributes to the voltage-dependence of mitochondrial porin channel.

The effects of pH on the integral conductance and on the properties of single channels induced by porin from rat liver mitochondria in a lipid bilayer have been studied. When the membrane potential increases, the conductance of the multi-channel membrane decreases more sharply at acidic pH than at neutral or basic pH. The channel is shown to have several states with different conductance and selectivity.

The gate of mitochondrial porin channel is controlled by a number of negative and positive charges.

Negatively charged carboxyl groups of mitochondrial porin have been converted into positively charged ones by means of reaction with water-soluble carbodiimide in the presence of ethylenediamine. Properties of channels formed in a planar lipid bilayer by native and modified porins are compared. Amidation has only little influence on the porin channel-forming activity as well as on the open-state conductance of the channel.

[Computer analysis of the spatial structure of the amphotericin channel].

Energy of Amphotericin B cholesterol complex in a membrane was calculated by the method of atom--atomic potentials. The complex is shown to have two stable states. One of them is stabilized by electrostatic interactions between charged groups of neighbouring antibiotic molecules due to a decline of the molecules to the pore radius.

Mechanism of anion-cation selectivity of amphotericin B channels.

Zero current potential and conductance of ionic channels formed by polyene antibiotic amphotericin B in a lipid bilayer were studied in various electrolyte solutions. Nonpermeant magnesium and sulphate ions were used to independently vary the concentration of monovalent anions and cations as well as to maintain the high ionic strength of the two solutions separated by the membrane. Under certain conditions the channels select very strongly for anions over cations.

Roflamycoin--a new channel-forming antibiotic.

Ion permeability of lipid bilayers was studied in the presence of a new antifungal pentaene antibiotic, roflamycoin, the structure of which differs considerably from that of the well-known polyene channel-former amphotericin B. Both of them, however, show the property of increasing the membrane permeability only in the case of sterol-containing membrane when added on both its sides. The conductance is strongly dependent on the concentration of the antibiotic in the solutions and of sterol in the membrane.

[Mathematical model of the interaction of cations and anions in a channel].

A mathematical model of the ionic channel permeable both to anions and cations is considered. The model takes into account the electrostatic interaction between oppositely charged ions and does not suppose single-file movement. An equation for zero-current potential is derived, which leads to the Goldman equation in the limit of low ion concentrations.

The dependence of the conductance and lifetime of gramicidin channels on the thickness and tension of lipid bilayers.

The lifetimes of channels formed by natural gramicidin and its dimeric analog in monoglyceride lipid bilayers of various compositions were investigated. The bilayer surface tension was altered by changing the length of the monoglycerides' fatty acid chain or the chain length of hydrocarbon solvent by isomerization or saturation of the lipid, by varying the amount of solvent in the bilayer, and by changing the salt composition of the aqueous solutions. The logarithms of mean channel lifetimes were found to be proportional to the surface tension of the membrane irrespective of how the surface tension was changed.

[Effect of bilayer lipid membrane thickness, composition, and tension on gramicidin channel parameters].

Dependence of channel parameters formed by gramicidin A (conductivity and mean life time) on thickness, composition and tension of planar bilayer lipid membranes (BLM) was studied. BLM were obtained from solutions of alpha-monoglycerides of fatty acids in n-alkanes. It has been shown that channel conductivity depends on the length of lipid radical hydrocarbon and is insensitive to the isomerization of lipid and to the change of solvent.

Mechanism of blockage of amphotericin B channels in a lipid bilayer.

A number of organic compounds (non-electrolytes, tetraalkylammonia, etc.) with a molecular size of 6--8 angstrom decrease the conductance of ionic channels formed in the lipid bilayer by a polyene antibiotic amphotericin B. It is suggested that these compounds, upon entering the channel, block the passage of inorganic ions.

How do ionic channel properties depend on the structure of polyene antibiotic molecules?

A study has been made of the properties of ionic channels formed in phospholipid-cholesterol bilayers by polyene antibiotics of various molecular structures. Properties of channels created by natural antibiotics with different structures of the lactone ring (amphotericin B-nystatin-mycoheptin) as well as by some derivatives of amphotericin B modified with respect to the amino and carboxyl groups are compared. Neutralization of one or both charges of the amphotericin B molecule (both by chemical modification and by pH shift) increases the probability of the channel to be in a nonconducting state.

[Relationship between ion channel properties and the structure of the lactone ring of polyene antibiotic molecules].

Properties of ionic channels created by amphoterecin B, nystatine and mycoheptin in phospholipid--cholesterol bilayer have been compared. Ionic conductivity and selectivity of channels as well as the frequency of transitions between an open state and a closed one depend on lacton ring structure. Appearance of one more carbonyl group in mycoheptin molecule leads to a decrease of channel anion permeability.

Properties of amphotericin B channels in a lipid bilayer.

Properties of individual ionic channels formed by polyene antibiotic Amphotericin B were studied on brain phospholipid membranes containing cholesterol. The ionic channels have a closed state and an open one (with conductance of about 6.5 pS in 2 M KCl).

[Electric conductivity of lipid membranes in the presence of proteolytic enzymes and their substrates].

It is shown that there are spasmodic changes of electroconductivity in bimolecular membranes in the presence of alpha-chimotripsin and denatured ovalbumin or glycyl-d,L-beta-phenylalanine. These conductivity changes are not due to the interaction ob proteolysis products with lipid bilayer but result from the interaction of alpha-chimo trypsin with the substrate or competing inhibitor. Probability of the state with a specific conductivity depends on the membrane voltage.

[Graph of sodium channel states].

Four models of sodium channel are considered, only one of its state being conducting. Transitions between any two communicated states are suggested to be governed by the first order kinetics. It is shown that the model describes current responses to single step potentials as well as inactivation -- activation coupling, if its graph has a function between the conducting and inactivation states and the state filled at the hyperpolarization.