Monazomycin-induced single channels. I. Characterization of the elementary conductance events.

Abstract

Monazomycin (a positively charged, polyene-like antibiotic) induces voltage-dependent conductance changes in lipid bilayer membranes when added to one of the bathing solutions . These conductance changes have generally been attributed to the existence of channels spanning the membrane . In this article we characterize the behavior of the individual conductance events observed when adding small amounts of monazomycin to one side of a lipid bilayer . We find that there are several apparent channel types with one or sometimes two amplitudes predominating . We find further that these fairly similar amplitudes represent two different states of the same fundamental channel entity, presumed to be the monazomycin channel . The current-voltage characteristics of these channels are weakly hyperbolic functions of applied potential . The average lifetimes are essentially voltage independent (between 50 and 400 mV). The average channel intervals, on the other hand, can be strongly voltage dependent, and we can show that the time-averaged conductance of a membrane is proportional to the average channel frequency .

Primary structure of peptides and ion channels. Role of amino acid side chains in voltage gating of melittin channels

“…Some have suggested that the helical dipole moment of the peptide chains lining the channel is a decisive determinant (23). It has also been argued that bound ions could supply the gating charge (24). Others have emphasized the potential role of charged groups on the side chains of the peptides (25).…”

Steady-state gating of batrachotoxin-modified sodium channels. Variability and electrolyte-dependent modulation.

“…The initial experiments (protocol I) were done using a low-pass integrator (Andersen and Muller, 1982) to obtain an analogue representation of the time-averaged single-channel current. The membrane potential was varied manually in 5-100-mV (usually 10-mV) steps, with 10-60-s sojourns at each level.…”

Monazomycin-induced single channels. II. Origin of the voltage dependence of the macroscopic conductance.

“…An interesting alternative involves consideration of a second poorly understood property of the system, namely, the molecular basis for the voltagedependent shift in the probability of the two conducting states of the monazomycin channels (Andersen and Muller, 1982) . The most attractive interpretation of the shift is that it represents two different aggregation states of the channel such that an aggregate of lower molecularity becomes stabilized at high V.…”

“…This is the second of two articles that describe the elementary events that underlie monazomycin-induced conductance (G) changes in planar lipid bilayers . In the preceding article (Andersen and Muller, 1982), we showed that the only characteristic of monazomycin channels that is not nearly invariant to changes in membrane potential (V) is the frequency of occurrence of the channels (f) . The purpose of this paper is to show that variations in channel frequency are indeed the basis for the voltage dependence of the monazomycin conductance .…”