Nuclear track-etched filters as model pores for biological membranes

A novel explanation for fluctuations of ion current through narrow pores

“…The effects of pH, ionic strength, and pore size on surface conductance correlate well with their effects on the diffusion of cations such as 86Rb or [3HJ choline across PETP membranes (13). Ion current through narrow PETP pores (14) an open configuration to a "closed" configuration results in the exposure of different charged residues near the pore, and hence a different selectivity (17). But if the pores through PETP membranes were to narrow in some way, the resulting selectivity would be higher, not lower (panels B and Fof Fig.…”

“…Moreover, reducing pH (e.g., from 9 to 5.5) does not alter pore size, since the rate of diffusion of water or nonelectrolytewhich is dependent on pore size-is unaffected by pH (13). That surface charge plays a dominant role for ion current and selectivity in PETP membranes is clearly shown by the fact that methylation of carboxyl groups to reduce surface charge has the anticipated effect of reducing ion current and selectivity: both parameters are less pH-sensitive, and the ionic strength dependence of current is that expected for an uncharged cylinder (14,18 At a selectivity of t+ = 0.95 (equivalent to a reversal potential of 48 mV for a 1:10 gradient), for example, a decrease in pH from 11 to 7 will cause conductance to fall by 50% whereas selectivity will fall to only 0.90 (equivalent to a reversal potential of 43 mV).…”

Controlled ion track etching

“…the liquid nanowire formation, along latent tracks. Eventually setting on current pulsations [2,[10][11][12] may mask the results to some extent. The technique is good for the controlled production of continuous transparent etched tracks in thin foils, as the conductivity changes rapidly during track etching over several orders of magnitude.…”

Ultrasound propagation in the micropores of track membranes

“…[8][9][10][11] TMs also serve as templates for the fabrication of micro-and nanostructured materials and as artificial objects mimicking biological membranes. 12,13 TMs fabricated of the polymer foils treated with ion beams from accelerators are especially suitable for model experiments because they may possess parallel pore channels oriented perpendicularly to the surface or tilted at a certain angle. 9,14 Propagation of electromagnetic waves was studied earlier to use TMs as soft x-ray, extreme ultraviolet and ultraviolet spectral filters.…”

“…This is an unexpected and anomalous behavior compared to other porous membranes that behave as homogeneous plates. [4][5][6][7][8][9][10][11][12][13][14][15][16][17] To explain this behavior we borrow some ideas from Biot's theory. 20,21 This theory predicts the appearance of one shear wave and two different compressional waves: a fast and a slow one ͑fluid and solid components move in phase and out of phase respectively͒.…”