Lipid-Dependent Gating of Kv Channels and Excitability Change of Cerebellar Purkinje Neurons in an NPC1 Model Mouse

Abstract

Recent studies of Kv channels in different membrane systems with altered ratios between phospholipids and nonphospholipids support our lipid-dependent gating hypothesis that the nonphospholipids favor the conformational switch of the voltage sensor domains of a Kv channel to a resting state. To enable more precise control of lipid composition in an artificial membrane and avoid possible solvent contamination or phase separation of lipids in bilayer membranes, we constructed a bead-supported unilamellar membrane (bSUM) and used it to define a more quantitative relationship between nonphospholipid content and change in the gating property of a voltage-gated potassium channel. In the bSUMs, we were able to show for the first time that a small amount of cholesterol (∼10 molar %) in a phospholipid membrane in a fluidic phase exerts a strong inhibitory effect on a KvAP channel, suggesting that the Kv channels might be highly sensitive to change in membrane cholesterol content. To test this prediction in a physiological system where lipid metabolic defects cause significant neurological disorders, we analyzed the neuronal excitability in a mouse model for the Niemann-Pick disease type C, an NPC1-I1061T knockin mice. Systematic comparison of five different groups of cerebellar Purkinje neurons from both knockin mice and control animals revealed a significant decrease in the firing frequency of action potentials in the tonic-burst firing Purkinje neurons of the NPC1 mice, which appears to be consistent with the predicted cholesterol effects on Kv channels. Detailed studies of the gating properties in these Purkinje neurons are being conducted to understand the underlying mechanism. Our data support a potential connection among cholesterol content in cell membranes, cholesterol-dependent gating of voltage-gated K channels and change in neuronal excitability in CNS neurons.