Membrane currents and pacemaking in corticotrophs and hiPSC-derived dopaminergic neurons

Abstract

Many neural networks are required to function at particular frequencies. These processes are often driven by rhythmic, intrinsically generated electrical activity that is produced by cells described as pacemaker neurons. Two disease-relevant in-vitro models were investigated that display poorly understood pacemaker activity; AtT20 anterior pituitary corticotrophs and human induced pluripotent stem cell (hiPSC)-derived dopaminergic (DA) neurons. Using electrophysiology and Ca2+ imaging, gaps in our understanding of pacemaking in these cell types were investigated. For AtT20s, it was revealed that hormone secretion in this cell type is uncoupled from its electrical activity. Novel roles were found for T-type voltage-gated calcium channels (VGCCs) in pacemaking and for L-type VGCCs in maintaining intracellular Ca2+ concentrations. hiPSC-derived DA neurons were found to produce apparently spontaneous electrical activity in culture that was dependent upon L-type VGCCs. This pacemaking was not found to be intrinsic, instead being driven by and developing in parallel with synaptic input in culture. These DA neurons immunostained for the L-type VGCC subtype CaV1.3, which is involved in the death of DA neurons in Parkinson's disease. Using a novel cell death assay these neurons were found to be selectively susceptible to the DA toxin 6-hydroxydopamine but displayed a resistance to glutamate-induced excitotoxicity. Data here provides valuable information on the similarities and differences between these in-vitro models and their in-vivo counterparts. This allowed for an in-depth assessment of their suitability as models for their respective diseases, hopefully leading to the targeted, efficient design of studies that use these cell types.