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

Abstract

Fluctuation and relaxation analyses were performed on monazomycin-induced conductance of lipid bilayer membranes. With both methods a slow (sec) and a fast (msec) current component are apparent; however, the amplitude of the slow, voltage-dependent process is greater than that of the fast component in the step relaxation experiment and less in the fluctuation experiment. The fluctuation analysis showed principally a rapid voltage-dependent process which appears to be related to the multistate character of the conducting channel. The experimental results are interpreted in terms of a simplified kinetic model which is used to calculate relaxation and noise amplitudes.

Decamethonium both opens and blocks endplate channels.

“…of DECA-induced membrane noise obtained under identical experimental conditions. Thus it can be concluded that the same two processes appear in both relaxation and noise experiments, in agreement with the fluctuation-dissipation theorem (23,24). However, fluctuation experiments are best suited to measure the fast process, whereas relaxation experiments are preferable for measurement of the slow process.…”

Conductance noise of monazomycin-doped bilayer membranes

“…According to the fluctuation-dissipation theorem (Onsager, 1931;Kubo, 1957) the correlation time ~' s should be identical with the relaxation time of a voltage-jump current relaxation experiment performed under comparable conditions. Relaxation experiments carried out with monazomycindoped bilayers also show for small changes in the applied voltage (A V~ V << 1) a slow time constant which decreases with increasing voltage (Muller & Finkelstein, 1972a;Moore & Neher, 1976). In contrast to relaxation experiments (Moore & Neher, 1976), the slow process could not be detected anymore at higher voltages by correlation analysis, since the value of oxy~ 9 A decreased beyond a detectable value of about 8 fS.…”

“…In the following, the fitted parameters of C(r) (variances and correlation times) obtained for a multi-pore system will be assigned to single-pore parameters by comparison of the results of the present paper with those obtained from single-pore experiments (Muller & Andersen, 1975;Bamberg & Janko, 1976) and from multi-pore voltage-jump current relaxation experiments (Muller & Finkelstein, 1972a;Moore & Neher, 1976). The results will also be compared with those measured in the presence of the antibiotic alamethicin, for which a similar strong voltage-dependent macroscopic conductance was found (Baumann & Mueller, 1974).…”

“…Relaxation experiments carried out with monazomycindoped bilayers also show for small changes in the applied voltage (A V~ V << 1) a slow time constant which decreases with increasing voltage (Muller & Finkelstein, 1972a;Moore & Neher, 1976). In contrast to relaxation experiments (Moore & Neher, 1976), the slow process could not be detected anymore at higher voltages by correlation analysis, since the value of oxy~ 9 A decreased beyond a detectable value of about 8 fS. This finding is in sha W contrast to the correlation analysis in the presence of alamethicin where % increased by orders of magnitude with increasing voltage and o~s2/~ 9 A stayed nearly constant .…”

“…From the correlation function of the fast conductance fluctuations, a single voltage-independent correlation time r I was found under the used experimental conditions, whereas noise analysis carried out by Moore and Neher (1976) and Wanke and Prestipino (1976) gave indications of further faster correlation times. For a voltage change up to 55 mV, r/remained unchanged within an experimental error of about 5% (see Table 1).…”