Increased anesthetic sensitivity in mice with <i>Scn8a</i>^<i>medJ</i><i>and Scn8a</i>^<i>9J</i>mutations.

<p>Best-fit dose response curves along with 95% confidence band (dashed lines) show the behavioral response (loss of righting reflex) of <i>Scn8a</i>^{<i>medJ/medJ</i>}<b>(A and B)</b> and <i>Scn8a</i>^<i>9J/9J</i><b>(C and D)</b> mice and their respective littermate control groups to increasing concentration of isoflurane and sevoflurane anesthesia. Seven mice were used for each group. Loss of righting reflex was used as a surrogate for unconsciousness. Filled (mutant mice) and open (littermate controls) squares represents the percentage of mice that lost the righting reflex in response to isoflurane <b>(A and C)</b> and sevoflurane <b>(B and D)</b>. Data were combined from two trials for each anesthetic and for each mouse. EC_50% shows a statistically significant (p<0.0001) leftward shift in the mutant mice, indicating hypersensitivity to anesthesia.</p

Effect of <i>Scn8a</i>^<i>medJ</i><i>and Scn8a</i>^<i>9J</i>mutations on the time to emergence from isoflurane and sevoflurane anesthesia.

<p>Compared to the littermate control mice, there was no significant difference in the time to emergence—return of righting reflex (RORR)—from isoflurane anesthesia (ISO) for either <i>Scn8a</i>^{<i>medJ/medJ</i>}<b>(A)</b> or <i>Scn8a</i>^<i>9J/9J</i><b>(C)</b> mice, or from sevoflurane anesthesia (SEVO) for <i>Scn8a</i>^{<i>medJ/medJ</i>}<b>(B)</b> mice. The mice with <i>Scn8a</i>^<i>9J</i> mutation <b>(D)</b> emerged significantly faster from sevoflurane anesthesia. Seven mice were used for each group. Data were combined from two trials for each anesthetic and for each mouse. ***p = 0.0002 compared to littermate control mice (Ctrl). S.D.—standard deviation.</p

Dominant Frequency Analysis.

<p><i>A. Sinus</i> rhythm 1 day prior to SUDEP, which is consistent with heart rate (728 bpm) analysis. B. Muscle artifact embedded in the sinus ECG (same as <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077843#pone-0077843-g009" target="_blank">Figure 9 C</a>) without any clear frequency peaks. C. High frequency electrical activity without any discernible sinus activity, consistent with VF (~25 Hz, same as <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077843#pone-0077843-g009" target="_blank">Figure 9, D and E</a>). D. PTZ induced seizures lead to a lower frequency electrical signal (~10 - 20 Hz). <i>Inset</i>: Representative snapshots of the ECG signal included in the fast-fourier transformation.</p

Altered Heart Rates Precede Death.

<p>A. DS mice exhibit significant QT prolongation (50 - 90%). B. Heart rates in DS mice decrease 100 min before death, followed by a sharp increase just prior to the terminal event, while the WT heart rates remains high and constant. (100 minutes = 10:16 PM in WT-1 and DS-1; 7:46 PM in WT-2 and DS-2). C. WT-3 and DS-3 HR cycling, followed by DS exhibiting sudden drops in heart rate in the 72 h preceding death. D and E. Increased R-R variability 60 min prior to SUDEP in DS-1 (blue) and DS-2 (red), respectively, with further increased variability immediately preceding the lethal arrhythmia, while 1 day prior at the same time the R-R interval was constant (black). F. Progressive bradycardia and increased R-R variability in DS-3 at several time points preceding an agonal state and euthanasia (denoted by colored arrows in C).</p

Isolation of TTX-R and TTX-S I_Na Biophysical Properties.

<p>A. Boltzman curves for the voltage dependence of I_Na availability and conductance for the total cardiac I_Na (TTX-S + TTX-R I_Na; reproduction of the curve-fits from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077843#pone-0077843-g001" target="_blank">Figure 1C</a>). In both WT and DS myocytes the V_½ values of TTX-R I_Na (closed circles, following blockade of TTX-S I_Na with 100 nM TTX) and TTX-S I_Na (open circles, defined as total I_Na minus TTX-R I_Na) are plotted. Pharmacological separation of TTX-S and TTX-R I_Na was confirmed by the loss of difference in the V_½ values between WT vs DS, and the development of a significant difference between the TTX-S vs. TTX-R V ½ values for I_Na availability and conductance. B. Zoom-in of the boxed region in A.</p

mScn5a and Nav1.5 levels are unchanged in DS mutant hearts.

<p>A. Heart RNA from biological replicates (DS mice, n = 4; WT mice, n = 5) were used to generate two independent cDNAs per animal. The cDNAs were assayed using qPCR in quadruplicate with two independent <i>Scn5a</i> TaqMan primer sets and normalized to 18s RNA. B. Western blots of membrane proteins isolated from DS and WT ventricular CMs. 50 µg of protein was loaded in each lane, and probed with anti-Na_v1.5 (Mohler 1:1000), and anti-α-actin (Sigma 1:500), which served as the loading control. C. Quantification of Na_v1.5 expression normalized to α-actin expression.</p

Cardiac Arrhythmias Precede SUDEP in DS.

<p>Lead II ECG traces illustrating cardiac arrhythmias preceding death. A-C. In mouse DS-2, muscle artifact consistent with convulsive seizures was preceded by idioventricular rhythms, including premature ventricular complexes (PVCs), bundle branch block (BBB), altered QRS morphology, and R-R variability. D and E. Initiation of high frequency electrical activity without any discernible sinus activity, consistent with VF. F. Low amplitude wide complex focal bradycardia with a BBB morphology, and eventual asystole. </p

DS Mice Have Altered Cardiac I_Na Properties.

<p>A. Current-voltage (I-V) relationship of transient I_Na. Peak transient I_Na density is increased 2-fold in the DS (N = 6, n = 14) vs WT cardiac myocytes (N = 8, n = 20, <i>p</i> < 0.0001). <i>Inset</i>: Representative traces from each group. B. I-V relationship for persistent I_Na (pre- minus post-30 µM TTX) also shows a 2-fold increase in peak persistent I_Na in the DS vs. WT groups. To further confirm these results we employed the P/4 method to measure the persistent I_Na, yielding similar results (-60 mV, WT, -1.72 ± 0.50; DS, -3.88 ± 0.72, N = 2, n = 5-9, <i>p</i> = 0.02). C. Leftward shift (V_½ of Boltzman fit, <i>p</i> = 0.04) in the voltage dependence of I_Na availability and conductance in the DS group. D. Similar percent change in peak transient I_Na density upon administration of 100 nM TTX in the WT and DS groups. Unpaired t-test with Welch’s correction.</p