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Biomedical subjects

G Ehrenstein

Publications and source records attributed to G Ehrenstein.

44 records · Page 3Linked to original sources
PubMed1971

Detection of molecular motion in lyophilized myelin by nuclear magnetic resonance.

Proton resonance spectroscopy was used to determine the state of the hydrocarbon regions in lyophilized and resuspended samples of nerve myelin. Measurements of the resonance line width indicate considerable freedom of motion within the hydrocarbon moiety of the myelin samples. Sharp thermal transitions of the line width were observed, suggesting that lyophilized myelin is in a liquid crystalline state.

Animals↗
PubMed1970

The nature of the negative resistance in bimolecular lipid membranes containing excitability-inducing material.

When sufficiently small amounts of excitability-inducing material (EIM) are added to a bimolecular lipid membrane, the conductance is limited to a few discrete levels and changes abruptly from one level to another. From our study of these fluctuations, we have concluded that the EIM-doped bilayer contains ion-conducting channels capable of undergoing transitions between two states of different conductance. The difference in current between the "open" and "closed" states is directly proportional to the applied membrane potential, and corresponds to a conductance of about 3 x 10(-10) ohm(-1). The fraction of the total number of channels that is open varies from unity to zero as a function of potential. The voltage-dependent opening and closing of channels explains the negative resistance observed for bimolecular lipid membranes treated with greater amounts of EIM.

Electrophysiology↗
PubMed1969

Effect of divalent cations on potassium conductance of squid axons: determination of surface charge.

Potassium conductance-voltage curves have been determined for a squid axon in high external potassium solution for a wide range of divalent cation concentrations. A decrease in divalent ion concentration shifts the conductance-voltage curve along the voltage axis in the direction of more hyperpolarized voltages by as much as 9 mv for an e-fold change in concentration. When the divalent ion concentration is less than about 5 mM, a further decrease does not cause a significant shift of the conductance-voltage curve. These results can be explained by assuming that on the outer surface of the membrane there is a negative fixed charge which can bind calcium ions, and that the axon is sensitive to the resulting double-layer potential. From our data, the best value for charge density was found to be one electronic charge per 120 square angstroms, and a lower limit to be one electronic charge per 280 square angstroms.

Animals↗
PubMed1967

Removal of potassium negative resistance in perfused squid giant axons.

Squid giant axons, internally and externally perfused with solutions having potassium as the only cation, exhibit an approximately linear steady-state current-voltage relation. When small amounts of calcium and magnesium are present in the external potassium solution, the current-voltage curve is markedly nonlinear, exhibiting the rectification and negative resistance which have been observed for intact axons in isosmotic potassium solutions. The effects of perfusion and removal of external divalent cations are interpreted in terms of two components of current, a linear component and a nonlinear time-varying component. The former is increased and the latter diminished by the removal of the external divalent cations.

Animals↗
PubMed1966

Slow changes of potassium permeability in the squid giant axon.

A slow potassium inactivation i.e. decrease of conductance when the inside of the membrane is made more positive with respect to the outside, has been observed for the squid axon. The conductance-potential curve is sigmoid shaped, and the ratio between maximum and minimum potassium conductance is at least 3. The time constant for the change of potassium conductance with potential is independent of the concentration of potassium in the external solution, but dependent upon potential and temperature. At 9 degrees C and at the normal sea water resting potential, the time constant is 11 sec. For lower temperature or more depolarizing potentials, the time constant is greater. The inactivation can be described by modifying the Hodgkin-Huxley equation for potassium current, using one additional parameter. The modified equation is similar in form to the Hodgkin-Huxley equation for sodium current, suggesting that the mechanism for the passive transport of potassium through the axon membrane is similar to that for sodium.

Animals↗