IMMUNOGLOBULIN-G FROM A PATIENT WITH MILLER-FISHER SYNDROME RAPIDLY AND REVERSIBLY DEPRESSES EVOKED QUANTAL RELEASE AT THE NEUROMUSCULAR-JUNCTION OF MICE

A neuromuscular blocking factor has been described in the serum of pat ients with Miller-Fisher syndrome (MFS). We here examined the effect o f immunoglobulins (Ig) on neuromuscular transmission in mice recording quantal endplate currents by means of a perfused macro-patch-clamp el ectrode. Ig and IgM- and IgG-fractions from an anti-GQ1b-positive pati ent with typical MFS were highly purified. After application of MFS-Ig G, quantal release decreased 1000-fold within 2 min. Returning to cont rol solution the average release came back to the baseline level withi n 4 min. In contrast, control-IgG and MFS-IgM did not cause any blocki ng effect. The very fast and fully reversible presynaptic blockade of release caused by the highly purified IgG-fraction may be one factor p roducing muscle weakness in MFS.