Reduction of calcium currents by Lambert-Eaton syndrome sera: Motoneurons are preferentially affected, and L-type currents are spared

Abstract

Previous work has demonstrated that Lambert-Eaton syndrome (LES) antibodies reduce calcium currents in non-neuronal cells and sensory neurons and reduce the amplitude of extracellularly recorded currents at mouse motor nerve terminals. We compared effects of LES sera on whole-cell currents of cultured nerve and muscle. LES sera more strongly reduced calcium currents in motoneurons than in sensory neurons. Motoneuronal potassium currents were unaffected. The sera minimally affected calcium currents in skeletal and cardiac muscle. In motoneurons, both low voltage-activated (LVA) and high voltage-activated (HVA) components of calcium current were decreased, demonstrating that the sera targeted more than one calcium channel type. The HVA current remaining in LES-treated motoneurons was little affected by micromolar ω-conotoxin MVIIC but was reduced >70% by micromolar nimodipine. This pharmacological profile contrasts with untreated cells and suggests that LES sera primarily spare L-type currents in motoneurons.