INHIBITION OF LOW-THRESHOLD AND HIGH-THRESHOLD CA2-EATON MYASTHENIC SYNDROME (LEMS) IGGS( CHANNELS OF HUMAN NEUROBLASTOMA IMR32 CELLS BY LAMBERT)

IgGs from two LEMS patients applied to human neuroblastoma IMR32 cells reduced the density of low- (LVA; T) and high-threshold (HVA; L and N ) Ba2+ currents by different percentages: 36% (LVA) and 56% (HVA) for one and 48% and 45% for the other. A pharmacological assay of IgGs act ion based on the block of L-type channel by nifedipine and on the dela yed activation of N-type channel by noradrenaline, indicated a prefere ntial inhibition of the N-type current in IMR32 cells (55% and 47% for the two patients). The L-type current, contributing to approximately one-third of the total, was also depressed by LEMS IgGs but to a minor degree (49% and 30%). Except for an increase of single N-type channel inactivation, LEMS antibodies preserved the elementary properties of single HVA channels, suggesting that the macroscopic current reduction after IgGs treatment is likely due to a decrease in the number of act ive HVA Ca2+ channels.