Involvement of Potassium and Cation Channels in Hippocampal Abnormalities of Embryonic Ts65Dn and Tc1 Trisomic Mice.
Down syndrome (DS) mouse models exhibit cognitive deficits, and are used for studying the neuronal basis of DS pathology. To understand the differences in the physiology of DS model neurons, we used dissociated neuronal cultures from the hippocampi of Ts65Dn and Tc1 DS mice. Imaging of [Ca(2+)]i and whole cell patch clamp recordings were used to analyze network activity and single neuron properties, respectively. We found a decrease of ~ 30% in both fast (A-type) and slow (delayed rectifier) outward potassium currents. Depolarization of Ts65Dn and Tc1 cells produced fewer spikes than diploid cells. Their network bursts were smaller and slower than diploids, displaying a 40% reduction in Δf / f0 of the calcium signals, and a 30% reduction in propagation velocity. Additionally, Ts65Dn and Tc1 neurons exhibited changes in the action potential shape compared to diploid neurons, with an increase in the amplitude of the action potential, a lower threshold for spiking, and a sharp decrease of about 65% in the after-hyperpolarization amplitude. Numerical simulations reproduced the DS measured phenotype by variations in the conductance of the delayed rectifier and A-type, but necessitated also changes in inward rectifying and M-type potassium channels and in the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. We therefore conducted whole cell patch clamp measurements of M-type potassium currents, which showed a ~ 90% decrease in Ts65Dn neurons, while HCN measurements displayed an increase of ~ 65% in Ts65Dn cells. Quantitative real-time PCR analysis indicates overexpression of 40% of KCNJ15, an inward rectifying potassium channel, contributing to the increased inhibition. We thus find that changes in several types of potassium channels dominate the observed DS model phenotype.
Department of Physics of Complex Systems, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100 Israel.
Shani
S
Stern
Department of Neurobiology, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100 Israel.
Menahem
M
Segal
Department of Physics of Complex Systems, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100 Israel.
Elisha
E
Moses
D000200:Action Potentials / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D018929:Cell Culture Techniques; D002478:Cells, Cultured; D004314:Down Syndrome / Q000235:genetics / Q000473:pathology / Q000503:physiopathology*; D005260:Female; D015870:Gene Expression; D006624:Hippocampus / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels / Q000235:genetics / Q000502:physiology*; D008297:Male; D057507:Mice, 129 Strain; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; C489469:Kir4.2 channel; D024661:Potassium Channels, Inwardly Rectifying; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin; D002118:Calcium
1D, one-dimensional; 2D, two-dimensional; DC, direct current; DS, Down syndrome; Down syndrome; EPSC, excitatory post synaptic current; GABA, gamma-aminobutyric acid; GIRK, G protein-coupled inwardly-rectifying potassium channels; HCN, hyperpolarization-activated cyclic nucleotide-gated; Hippocampus; Inward rectifiers; Potassium channels; Potassium currents; ROI, region of interest; RT-PCR, real time polymerase chain reaction; Reduced excitability; SEM, standard error of mean; TTX, tetrodotoxin; Tc1; Ts65Dn; WT, wild type