Excess electrical noise during current flow through porous membranes separating ionic solutions

Abstract

Spectral analysis of electrical noise from various artificial membrane systems suggests that excess noise of an f-n spectral form, where n is approximately unity, is not primarily a bulk phenomenon simply dependent on the number of charge carriers. Measurements from aqueous and nonaqueous electrolytic resistors, comprised of several different ionic species, show only flat power density spectra under applied currents, even at extreme dilutions. Excess noise of f-n form is observed under applied d-c current in single pore membranes, as previously reported, but is also seen in multipore and polymer mesh membranes. Calculations based on single pore membrane noise data are in significant variance with the bulk charge carrier model proposed by Hooge. These observations suggest that such excess noise occurs in conjunction with anisotropic constraints to ion flow.

1/f noise in black lipid membranes induced by ionic channels formed by chemically dimerized gramicidin A

“…The chemically dimerized form of gramicidin A seems, therefore, to constitute an ionic channel per se without any further molecular association. This conclusion is also largely confirmed by the finding of a 1If power spectrum with malonyl-bis-desformylgramicidin, as in systems consisting of large holes in thick artificial membranes (DeFelice & Michalides, 1972;Dorset & Fishman, 1975). The failure to detect intermolecular associations among malonyl-bis-desformylgramicidin molecules is particularly important, since it substantiates the argumentation recently proposed by Bamberg, Apell and Alpes (1977) in favor of Urry's model for the molecular structure of the gramicidin A channel.…”

“…Such a value is far above the actual estimate obtained with malonyl-bis-desformylgramicidin channels, though a direct comparison between Hooge's equation and the present results remains questionable. However, the above discrepancy seems to indicate that, despite a formalism which appears to be totally valid, Hooge's equation cannot be applied without restrictions to any kind of membrane system, unless a clearer physical interpretation of the parameter c~ is provided (Stevens, 1972;Dorset & Fishman, 1975;DeGoede & Verveen, 1977;Van denBerg et aI., 1977). Results on the dependency of 7 [see Eq.…”

“…However, by comparing our results to those obtained with large holes in thick membranes, it seems clear that the physical entities which are responsible for the transport of ions across the membrane phase are not the determining factors. The transport of ions through a 0.4 nm wide long lasting channel is certainly not equivalent to a simple nonselective constrained flow of ions through a large aqueous pore; nevertheless, both cases lead to a 1If power spectrum (Green & Yafuso, 1968;Hooge, 1970;Hooge & Gaal, 1971;DeFelice & Michalides, 1972;Dorset & Fishman, 1975;Lifson et al, 1978). Our study indicates that the intensity of the 1If component of Sin(f) depends to a large extent upon membrane parameters such as R~, I,, and e, though the exact nature of e needs to be determined.…”

“…Shall we expect with the chemically dimerized form of gramicidin A a Lorentzian type power spectrum (constant value at low frequencies, 1/f 2 behavior for f > fc, fc being the corner frequency) as in the case of normal gramicidin A, but with a lower corner frequency, or do we have to look for a totally different noise behavior? In this regard it is worth mentioning that power spectra of the type 1/f have been found with systems consisting of thick artificial membranes containing long lasting aqueous pores (Green & Yafuso, 1968 ;Hooge, 1970;Hooge & Gaal, 1971 ;DeFelice & Michalides, 1972;Dorset & Fishman, 1975;Lifson, Gavish & Reich, 1978). Since the chemically dimerized form of gramicidin A creates long lasting channels, a similar noise behavior can be expected, though the two systems are not totally equivalent; in one case we have large holes in thick membranes, whereas this gramicidin A derivative forms cation selective channels in black lipid membranes.…”

Fluctuation and relaxation analysis of monazomycin-induced conductance in black lipid membranes

“…For membrane systems this distinction is important, since 1/f noise can be observed in essentially all permeability barriers as a manifestation of nonspecific ion channels (Dorset & Fishman, 1975;Verveen & De Felice, 1974).…”