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Involvement of Potassium and Cation Channels in Hippocampal Abnormalities of Embryonic Ts65Dn and Tc1 Trisomic Mice.

Stern S, Segal M, Moses E - EBioMedicine (2015)

Bottom Line: We found a decrease of ~ 30% in both fast (A-type) and slow (delayed rectifier) outward potassium currents.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics of Complex Systems, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100 Israel.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

Experimental measurement and numerical simulation of potassium currents. a–f, Experimental results under voltage clamp with voltage steps going from− 90 mV to 80 mV. The currents are normalized by the estimated capacitance of the cell (see Methods). Fast currents are measured as the peak current a few milliseconds after the depolarization step. Slow currents are measured towards the end of the depolarizing step, which occurs 300 ms after its beginning. a, Example recording of potassium currents for a diploid cell. The current is normalized by the capacitance of the cell. Top inset: Zooming in on the first 50 ms of recording, the fast currents can be observed as the peak current a few milliseconds after the voltage step. Bottom inset: Fast currents are eliminated by application of 2 mM 4-aminopyridine indicating that they are mostly A-type potassium currents. b, Example recording of potassium currents for a Ts65Dn cell. The current is normalized by the capacitance of the cell. Top inset: Zooming in on the first 50 ms of recording, the fast currents can be observed as the peak current a few milliseconds after the voltage step. Bottom inset: Fast currents are eliminated by application of 2 mM 4-aminopyridine indicating that they are mostly A-type potassium currents. c, Fast potassium currents of diploid neurons (N = 23 cells) are larger compared to Ts65Dn neurons (N = 27 cells), p = 0.0004. d, Slow potassium currents of diploid neurons (N = 23 cells) are larger compared to Ts65Dn neurons (N = 27 cells), p = 0.008. e, Fast potassium currents of diploid neurons (N = 36 cells) are larger compared to Tc1 neurons (N = 36 cells), p = 0.0021. f, Slow potassium currents of diploid neurons (N = 36 cells) are larger compared to Tc1 neurons (N = 36 cells), p = 0.082. For panels c–f data are presented as mean ± SEM. g, h, Simulation results. g, The fast potassium currents measured in simulated DS cells compared to those measured in WT cells. h, Simulated slow potassium currents in DS cells compared to WT cells.
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f0025: Experimental measurement and numerical simulation of potassium currents. a–f, Experimental results under voltage clamp with voltage steps going from− 90 mV to 80 mV. The currents are normalized by the estimated capacitance of the cell (see Methods). Fast currents are measured as the peak current a few milliseconds after the depolarization step. Slow currents are measured towards the end of the depolarizing step, which occurs 300 ms after its beginning. a, Example recording of potassium currents for a diploid cell. The current is normalized by the capacitance of the cell. Top inset: Zooming in on the first 50 ms of recording, the fast currents can be observed as the peak current a few milliseconds after the voltage step. Bottom inset: Fast currents are eliminated by application of 2 mM 4-aminopyridine indicating that they are mostly A-type potassium currents. b, Example recording of potassium currents for a Ts65Dn cell. The current is normalized by the capacitance of the cell. Top inset: Zooming in on the first 50 ms of recording, the fast currents can be observed as the peak current a few milliseconds after the voltage step. Bottom inset: Fast currents are eliminated by application of 2 mM 4-aminopyridine indicating that they are mostly A-type potassium currents. c, Fast potassium currents of diploid neurons (N = 23 cells) are larger compared to Ts65Dn neurons (N = 27 cells), p = 0.0004. d, Slow potassium currents of diploid neurons (N = 23 cells) are larger compared to Ts65Dn neurons (N = 27 cells), p = 0.008. e, Fast potassium currents of diploid neurons (N = 36 cells) are larger compared to Tc1 neurons (N = 36 cells), p = 0.0021. f, Slow potassium currents of diploid neurons (N = 36 cells) are larger compared to Tc1 neurons (N = 36 cells), p = 0.082. For panels c–f data are presented as mean ± SEM. g, h, Simulation results. g, The fast potassium currents measured in simulated DS cells compared to those measured in WT cells. h, Simulated slow potassium currents in DS cells compared to WT cells.

Mentions: The changes in action potential amplitude, AHP amplitude and spike threshold observed in both DS mouse models point to reduced potassium currents. Potassium currents were then measured in cultured Ts65Dn and Tc1 hippocampal neurons under voltage clamp while blocking sodium currents with TTX. The slow and fast components of the potassium currents were measured (see Methods), and were found to be significantly smaller in both DS mouse model neurons compared to diploids. An example of a recording of potassium currents is shown in Fig. 5a and b. The fast current is also displayed on the small upper inset of these figures, zooming in on the first few milliseconds of recording. The lower inset shows a recording with 4A-P applied at 2 mM. As can be seen the fast currents are eliminated, indicating that these are mainly A-type potassium currents. A total of 23 diploid neurons and 27 Ts65Dn neurons were measured, and their results are plotted in Fig. 5c (fast) and d (slow). Similarly, a total of 36 diploid neurons and 36 Tc1 neurons were measured, and their results are plotted in Fig. 5e (fast) and f (slow).


Involvement of Potassium and Cation Channels in Hippocampal Abnormalities of Embryonic Ts65Dn and Tc1 Trisomic Mice.

Stern S, Segal M, Moses E - EBioMedicine (2015)

Experimental measurement and numerical simulation of potassium currents. a–f, Experimental results under voltage clamp with voltage steps going from− 90 mV to 80 mV. The currents are normalized by the estimated capacitance of the cell (see Methods). Fast currents are measured as the peak current a few milliseconds after the depolarization step. Slow currents are measured towards the end of the depolarizing step, which occurs 300 ms after its beginning. a, Example recording of potassium currents for a diploid cell. The current is normalized by the capacitance of the cell. Top inset: Zooming in on the first 50 ms of recording, the fast currents can be observed as the peak current a few milliseconds after the voltage step. Bottom inset: Fast currents are eliminated by application of 2 mM 4-aminopyridine indicating that they are mostly A-type potassium currents. b, Example recording of potassium currents for a Ts65Dn cell. The current is normalized by the capacitance of the cell. Top inset: Zooming in on the first 50 ms of recording, the fast currents can be observed as the peak current a few milliseconds after the voltage step. Bottom inset: Fast currents are eliminated by application of 2 mM 4-aminopyridine indicating that they are mostly A-type potassium currents. c, Fast potassium currents of diploid neurons (N = 23 cells) are larger compared to Ts65Dn neurons (N = 27 cells), p = 0.0004. d, Slow potassium currents of diploid neurons (N = 23 cells) are larger compared to Ts65Dn neurons (N = 27 cells), p = 0.008. e, Fast potassium currents of diploid neurons (N = 36 cells) are larger compared to Tc1 neurons (N = 36 cells), p = 0.0021. f, Slow potassium currents of diploid neurons (N = 36 cells) are larger compared to Tc1 neurons (N = 36 cells), p = 0.082. For panels c–f data are presented as mean ± SEM. g, h, Simulation results. g, The fast potassium currents measured in simulated DS cells compared to those measured in WT cells. h, Simulated slow potassium currents in DS cells compared to WT cells.
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Related In: Results  -  Collection

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f0025: Experimental measurement and numerical simulation of potassium currents. a–f, Experimental results under voltage clamp with voltage steps going from− 90 mV to 80 mV. The currents are normalized by the estimated capacitance of the cell (see Methods). Fast currents are measured as the peak current a few milliseconds after the depolarization step. Slow currents are measured towards the end of the depolarizing step, which occurs 300 ms after its beginning. a, Example recording of potassium currents for a diploid cell. The current is normalized by the capacitance of the cell. Top inset: Zooming in on the first 50 ms of recording, the fast currents can be observed as the peak current a few milliseconds after the voltage step. Bottom inset: Fast currents are eliminated by application of 2 mM 4-aminopyridine indicating that they are mostly A-type potassium currents. b, Example recording of potassium currents for a Ts65Dn cell. The current is normalized by the capacitance of the cell. Top inset: Zooming in on the first 50 ms of recording, the fast currents can be observed as the peak current a few milliseconds after the voltage step. Bottom inset: Fast currents are eliminated by application of 2 mM 4-aminopyridine indicating that they are mostly A-type potassium currents. c, Fast potassium currents of diploid neurons (N = 23 cells) are larger compared to Ts65Dn neurons (N = 27 cells), p = 0.0004. d, Slow potassium currents of diploid neurons (N = 23 cells) are larger compared to Ts65Dn neurons (N = 27 cells), p = 0.008. e, Fast potassium currents of diploid neurons (N = 36 cells) are larger compared to Tc1 neurons (N = 36 cells), p = 0.0021. f, Slow potassium currents of diploid neurons (N = 36 cells) are larger compared to Tc1 neurons (N = 36 cells), p = 0.082. For panels c–f data are presented as mean ± SEM. g, h, Simulation results. g, The fast potassium currents measured in simulated DS cells compared to those measured in WT cells. h, Simulated slow potassium currents in DS cells compared to WT cells.
Mentions: The changes in action potential amplitude, AHP amplitude and spike threshold observed in both DS mouse models point to reduced potassium currents. Potassium currents were then measured in cultured Ts65Dn and Tc1 hippocampal neurons under voltage clamp while blocking sodium currents with TTX. The slow and fast components of the potassium currents were measured (see Methods), and were found to be significantly smaller in both DS mouse model neurons compared to diploids. An example of a recording of potassium currents is shown in Fig. 5a and b. The fast current is also displayed on the small upper inset of these figures, zooming in on the first few milliseconds of recording. The lower inset shows a recording with 4A-P applied at 2 mM. As can be seen the fast currents are eliminated, indicating that these are mainly A-type potassium currents. A total of 23 diploid neurons and 27 Ts65Dn neurons were measured, and their results are plotted in Fig. 5c (fast) and d (slow). Similarly, a total of 36 diploid neurons and 36 Tc1 neurons were measured, and their results are plotted in Fig. 5e (fast) and f (slow).

Bottom Line: We found a decrease of ~ 30% in both fast (A-type) and slow (delayed rectifier) outward potassium currents.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics of Complex Systems, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100 Israel.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus