ISSN:
0091-7419
Keywords:
Life Sciences
;
Molecular Cell Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Alamethicin, monazomycin, or EIM induce electrical excitability in lipid bilayers. The voltage-dependent gating displays all the characteristics observed in excitable cells and its basic features can be quantitatively described by the Hodgkin-Huxley equations.A common molecular mechanism of membrane excitation has been postulated. It assumes that in the absence of an electrical field the channel-forming molecules lie at the surface of the membrane. An applied potential tilts them from the surface into the hydrocarbon region of the bilayer. Once in this position the molecules diffuse laterally and form aggregates which act as channels for the flow of ions.In the case of alamethicin we assume that the molecule forms an elongated ellipsoid with two glutamic residues at one end, and a metal ion in four- or five-fold coordination with peptide carbonyl oxygens at the other. An applied field pulls the cationic end through the membrane to the other side, while the glutamic residues hold the other end attached to the original surface. The molecules now span the membrane and aggregate, forming oligomeric channels in which most of the peptide carbonyls face toward the center, and the methyl groups outward.Monomers and dimers do not conduct and an individual channel can have different conductance values depending on the number of monomers in the aggregate and the resulting channel diameter. A quantitative description of this process matches observed gating kinetics, gating currents, and the single channel conductance increments. Without additional assumptions, inactivation follows directly from the aggregation process because with proper rate constants, the average degree of polymerization and therefore number of open channels goes through a maximum in time.The model may also apply to the excitation process of higher cells.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jss.400020504
