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Biomedical subjects

H G Coster

Publications and source records attributed to H G Coster.

34 records · Page 2Linked to original sources
PubMed1975

Electromechanical stresses and the effect of pH on membrane structure.

The presence of an electric field in a membrane creates stresses which lead to a mechanical compression of the membrane material. It is shown that considerations of this effect yield results consistent with the observed differential effect of pH on the plasma membrane substructure if the central electron-lucent layer in OsO4-fixed membranes is identified with the ionic depletion in the double-fixed charge model of cell membranes.

Cell Membrane↗
PubMed1973

The double fixed charge membrane. Low frequency dielectric dispersion.

An analysis is made of the AC characteristics of a membrane consisting of two fixed charge regions of opposite sign, in contact. It is shown that the equivalent parallel capacitance and conductance of such a membrane undergo a strong dispersion at low frequencies. The dielectric dispersion is a result of polarization effects in the diffusion of coions in each of the two fixed charge lattices. This, at low frequencies, gives rise to a very large diffusion capacitance. The form of the dispersion characteristics is very similar to those observed for synthetic-fused anion-cation membranes and various cellular membranes.

Electric Conductivity↗
PubMed1973

The double fixed charge membrane. Solution-membrane ion partition effects and membrane potentials.

An analysis is made of the effect of solution-membrane partition of ions on the electrostatic potential and ion concentration profiles in fixed charge membranes. It is shown that the inclusion of partition effects gives rise to large solution-membrane "Donnan" potentials even when the concentration of fixed charges is of the same order as the concentration of the external solution. This effect renders the system and the simplified analysis of the double fixed charge membrane (FCM) previously given more applicable to biological membranes. An analysis is also given of the voltage dependence of the fluxes of individual ion species in the double FCM when it separates different ionic solutions and an expression is deduced for the membrane resting potential. Although the latter is similar in form to the Goldman-Hodgkin-Katz (GHK) equation the corresponding value of the permeability ratio P(C1)/P(K) is under certain specified conditions both concentration and potential dependent.

Ions↗
PubMed1969

The electrical characteristics of fixed charge membranes: solution of the field equations.

A theoretical analysis is made of the electrical characteristics of a membrane containing two fixed charge regions, of opposite sign, in contact. Profiles of ion concentrations, electrostatic potential, space charge density, as well as the voltage-current characteristics were obtained by numerical integration of the field equations on a computer. Comparison with the predictions of an earlier analysis of this system (Coster, 1965) shows that the latter is valid to a good approximation for membranes > 70 A in thickness. In particular the form of the electrical characteristics, including the punch-through effect, have been verified by the computer analysis. The range of useful validity of the earlier analysis, the use of Boltzmann statistics when currents are present, and variation of membrane capacitance with applied potential, are discussed in the light of the results obtained.

Computers↗
PubMed1968

A thermodynamic analysis of fluxes and flux-ratios in bioligical membranes.

Flux and flux-ratio equations are derived on the basis of the phenomenological equations of irreversible thermodynamics. Deviations of flux-ratios from that given by the often quoted Ussing (1949) relation are predicted, even in the absence of active transport, by considering the dependence of coupled fluxes on the membrane potential. The treatment is extended to include the interpretation of fluxes measured with tracers. Estimation of the numerical values of the resistance coefficients show that the voltage dependence of the entrainment terms can adequately account for the departures from the Ussing relation and the discrepancies between isotopically and electrically measured membrane conductances.

Biological Transport, Active↗
PubMed1965

A quantitative analysis of the voltage-current relationships of fixed charge membranes and the associated property of "punch-through".

A theoretical analysis of the voltage-current relationship is carried out in a membrane consisting of two fixed charge regions, of opposite sign, in contact. This is achieved by applying the diffusion equations to this system in conjunction with the Poisson-Boltzmann equation. The latter has been successfully applied by Mauro to determine the profiles of the electrostatic potential in his treatment of the capacitative property of such a system. It is shown that the system displays the property of rectification and is very similar in many respects to a solid state P-N junction diode. It is also shown that for the case of reverse bias, an electrical breakdown phenomena can occur. This is referred to as the "punch-through" effect. "Punch-through" was observed in experiments on the electrical characteristics of the membranes of Chara australis and Nitella sp. The experimental results are discussed in relation to the theoretical analysis.

Cell Membrane↗