Differential blocking effects of the monoclonal anti-GQ1b IgM antibody and alpha-latrotoxin in the absence of complement at the mouse neuromuscular junction.

Numerous in vitro electrophysiological studies found different effects of anti-ganglioside antibodies on neuromuscular transmission. Since a complement-dependent, latrotoxin-like effect has been described for the mouse monoclonal anti-GQ1b IgM antibody (termed CGM3), we here investigated the effect of CGM3 and alpha-latrotoxin by means of the perfused macro-patch clamp electrode in mice hemidiaphragms in the absence of complement. The CGM3 mab depressed evoked quantal release dose-dependently, whereas the rate of spontaneous releases and the amplitude of postsynaptic currents was not significantly affected. Alpha-latrotoxin induced an increase in spontaneous releases followed by a blockade of evoked quantal release, this was not altered by CGM3. The complement-independent presynaptic block by CGM3 was different from the action of alpha-latrotoxin.