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A FINKELSTEIN

Publications and source records attributed to A FINKELSTEIN.

16 recordsLinked to original sources
PubMed1976

Black widow spider venom: effect of purified toxin on lipid bilayer membranes.

A purified toxin (the B5 fraction) from black widow spider venom added to the solution on one side of a lipid bilayer membrane interacts irreversibly with the membrane to produce a continuous, linear rise of membrane conductance with time. Conductances greater than 10(-4) reciprocal ohm per square centimeter can eventually be attained without any loss of membrane stability. Membranes treated with toxin are ideally selective for alkali cations over anions and are substantially permeable to calcium ion. These effects of the toxin result from the formation of permanent channels in the membrane of uniform conductance, 3.6 X 10(-10) reciprocal ohm (in 0.1 molar potassium chloride), that remain open almost all the time. Both the divalent cation permeability and the smaller conductances at low pH of toxin-treated membranes suggest that there is negative charge (possibly from carboxyl groups) associated with the channels. We discuss the possible relation of the action of this toxin on lipid bilayer membranes to its ability to stimulate massive transmitter release at the neuromuscular junction and to produce profound morphological changes on tissue cultured neurons.

Black Widow Spider↗
PubMed1964

CARRIER MODEL FOR ACTIVE TRANSPORT OF IONS ACROSS A MOSAIC MEMBRANE.

The central purpose of this paper is to elucidate in a well defined system the meaning of certain phenomena and concepts associated with the active transport of ions. To this end a specific model for a carrier system which actively transports a single ionic species is analyzed and discussed in detail. It is assumed in this model that the carrier-mediated ionic transport occurs in regions of the membrane physically separate from those regions in which free ionic movement takes place,-coupling between the active and passive regions of the membrane occurring through local current flows. The model is seen to display the following characteristics: (a) Starting from identical solutions on the two sides of the membrane, there is produced a redistribution of ions; (b) with identical solutions on the two sides of the membrane there exists a potential difference across the membrane, i.e., the "pump" is electrogenic; (c) the "short circuit" current for symmetrical solutions is equal to the flux of the neutral ion carrier complex; (d) the rate of active transport (and hence of metabolism) is dependent on the ionic concentrations in the surrounding solutions. Throughout the paper comparison is made between features of the model and properties displayed by biological active transport systems, but there is no claim of an identity between the two.

Biological Transport↗
PubMed1964

ELECTRICAL EXCITABILITY OF ISOLATED FROG SKIN AND TOAD BLADDER.

When current of proper polarity and sufficient intensity is passed across isolated frog skin or toad bladder, an action potential of about 200 mv and 10 msec. duration with a sharp threshold and refractory period of several seconds' duration is elicited. Interruption of current during the action potential abolishes the response, and, as shown by appropriate bridge measurements, this occurs because the action potential results from resistance variations during the current flow. The ionic composition of the medium bathing the frog skin was varied, and it was found that the response is relatively insensitive to changes in the solution bathing the inner surface, but rapidly and reversibly affected by changes in the outer solution, particularly by replacement of sodium with potassium and by variations of calcium concentration. It was also observed that the resistance of the skin and action potential across it are reversibly altered by metabolic inhibitors and that these alterations occur independently of any changes in the intrinsic EMF of the system. From the finding that the action potential across frog skin and toad bladder results from a time-variant resistance, it is argued that this same phenomenon can be the basis of electrical excitability in general. This would attribute physical significance to the equivalent circuit commonly employed to represent the plasma membrane; i.e., the plasma membrane would be a mosaic structure of spatially separate permselective regions.

Action Potentials↗
PubMed1961

Lithium-induced oscillations of potential and resistance in isolated frog skin.

The rhythmical variations of electrical potential and DC resistance resulting from the exposure of the anatomical outside of isolated frog skin to a concentration of lithium ion greater than 20 millinormal were reinvestigated. In general, the potential and resistance changes were in phase, although in some skins, a phase shift occurred after the first few waves. The mean level of the resistance declined during the exposure to lithium, returning to its former level upon reintroduction of sodium in place of lithium. The oscillations, with a period of from 3 to 15 minutes, could last for 2 hours or more before damping out; the amplitude of the waves could be altered during this time by the passage of direct current or by the introduction of a hydrostatic pressure difference across the skin. Even after the oscillations damped out, the system remained "excitable," responding to a step of direct current or hydrostatic pressure with an oscillatory train. The nature and magnitude of the response to current and pressure were dependent upon the "polarity" of the applied perturbation. Direct observation of the skin revealed no evidence of oscillatory water movement concomitant with the electrical events.

Animals↗
PubMed1958

Realistic model of a fixed-charge membrane according to the theory of Teorell, Meyer, and Sievers.

A realistic model of a fixed-charge membrane was constructed to elucidate the principles involved in the Teorell-Meyer-Sievers theory. Polyelectrolyte solutions (polystyrene sulfonic acid or gelatin) were used in a multicompartment cell to serve as the "membrane." The ionic concentration and potential differences between the compartments served as a finite increment approximation to a continuous membrane phase. The profiles obtained for a positively and negatively charged membrane gave striking support for the theory.

Electrophysiology↗
PubMed1955

Cholangiography.

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Biliary Tract↗