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Related Experiment Videos

Channel fluctuations induced by membrane attack complex C5B-9.

J D Young1, T M Young

  • 1Laboratory of Cellular Physiology and Immunology, Rockefeller University, New York, NY 10021.

Molecular Immunology
|October 1, 1990
PubMed
Summary
This summary is machine-generated.

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The complement (C) system

Area of Science:

  • Immunology
  • Molecular Biology
  • Biophysics

Background:

  • The terminal complement pathway, involving C5b-9 complexes, forms membrane attack complexes (MACs) that cause cell lysis.
  • The role of C9 polymerization in MAC-mediated cytolysis is debated, as cell lysis can occur without visible tubular formation.
  • Previous studies have attributed membrane damage to large tubular structures formed by polymerized C9.

Purpose of the Study:

  • To investigate the channel-forming properties of C5b-9 complexes reconstituted in artificial lipid bilayers.
  • To characterize the conductance and ion selectivity of C5b-9 channels.
  • To elucidate the mechanism of membrane damage by the terminal complement pathway.

Main Methods:

  • Reconstitution of C5b-9 complexes into high-impedance planar lipid bilayers.

Related Experiment Videos

  • Electrophysiological recordings to measure unitary channel conductances.
  • Voltage-dependence and ion selectivity measurements using different salt concentrations.

    • Main Results:

    • C5b-9 complexes formed heterogeneous ion channels in lipid bilayers, with the smallest exhibiting 15 pS conductance in 0.1 M NaCl.
    • These small channels displayed voltage-dependent gating and cation selectivity, favoring K+ over Na+.
    • The observed 15-pS channels resembled those formed by the non-polymerizing C9b fragment, not large polymerized C9 structures.

    Conclusions:

    • C5b-9 complexes initiate membrane damage by forming small, discrete ion channels.
    • These initial small channels may aggregate to form larger, tubular lesions characteristic of MACs.
    • C5b-8 increases membrane permeability through lipid perturbation, while C9 addition generates authentic ion channels.