IgM anti-GQ1b monoclonal antibody inhibits voltage-dependent calcium current in cerebellar granule cells

Miller-Fisher syndrome (MFS), which is known to be associated with anti-GQ1b antibodies and to cause ataxia, is a variant of an acute inflammatory neuropathy. However, the pathogenic role of anti-GQ1b antibodies remains unclear. In this study, we investigated the effects of mouse IgM anti-GQ1b monoclonal antibody (IgM anti-GQ1b mAb) on the spontaneous muscle action potential of a rat spinal cord-muscle co-culture system and on the voltage-dependent calcium channel (VDCC) current in cerebellar granule cells and Purkinje cells using the whole-cell patch clamp technique. The frequency of spontaneous muscle action potential of the innervated muscle cells was transiently increased by IgM anti-GQ1b mAb and then was blocked completely, which was the same finding as reported previously. Moreover, the cerebellar granule cell VDCC current was decreased by 30.76+/-7.60% by 5 microg/mL IgM anti-GQ1b mAb, whereas IgM anti-GQ1b mAb did not affect the VDCC current in cerebellar Purkinje cells. In immunocytochemistry, IgM anti-GQ1b mAb stained the whole cell surface of cerebellar granule cells, but not that of Purkinje cells. Therefore, the clinical symptoms of Miller-Fisher syndrome, such as cerebellar-like ataxia, may be explained by the inhibitory effects of anti-GQ1b antibodies on VDCC current in cerebellar granule cells.