Effect of Ca_v3.1 I–II loop deletions on the voltage dependence of channel activation.

<p><i>A, B,</i> Normalized current traces recorded during depolarizing voltage steps from −80 to +30 mV (holding potential, −100 mV, except for GD1–2 mutant, which due to shifted inactivation was −110 mV) in WT Ca_v3.1 (<i>Aa</i>), GD1–2 (<i>Ab</i>), GD3–5 (<i>Ac</i>), WT Ca_v3.3 (<i>Ba</i>), ID1–2 (<i>Bb</i>) and ID3–5 (<i>Bc</i>). Thick gray lines represent the current at −50 mV, demonstrating the negative shift in voltage dependence of activation observed in the deletion mutants. Currents were normalized to the maximum peak current in that cell. Time calibration bar scale applies to all three sets of traces in each case. Peak current-voltage plots for either Ca_v3.1 and its deletions (<i>C</i>) or Ca_v3.3 and its deletions (<i>D</i>). Peak currents were normalized to the cell size as estimated by capacitance. Normalized current-voltage plots for either Ca_v3.1 and its deletions (<i>E</i>) or Ca_v3.3 and its deletions (<i>F</i>). Same symbol definition as in panels <i>C</i> and <i>D</i>. Smooth curves in <i>C–F</i> represent fits to the average data using a Boltzmann–Ohm equation <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002976#pone.0002976-AriasOlgun1" target="_blank">[4]</a>.</p

Effect of deletions on channel surface expression as measured by electrophysiology and luminometry.

<p><i>A,B,</i> The <i>I-V</i> data from each cell was fit with a Boltzmann-Ohm equation to calculate <i>V_0.5</i>, <i>k</i>, <i>G_max</i>, and <i>E_rev</i>. The value of <i>E_rev</i> was then used to calculate the chord conductance at each test potential. These data were then normalized for cell capacitance. Only the increase in GD3–5 conductance (G_max) was statistically different than control Ca_v3.1. <i>C,</i> Luminometric quantification of the expression levels of HA-tagged Ca_v3.1 and Ca_v3.3 channel variants at the membrane (non-permeabilized). Average relative light units (RLU) for WT channels before normalization were: Ca_v3.1, 2,867,417±551,473; and Ca_v3.2 2,533,150±353,578, n = 6 for both). To reduce the error between experiments the data were normalized to the membrane expression for the respective WT channel. Total expression of HA-tagged channels measured after Triton X-100 permeabilization normalized to membrane expression. Ratio of surface/total expression identifies an increase in membrane expression for GD3–5, and decreases in GD1–2, ID1–2, and ID3–5. Statistically significant differences from control wild-type channels are indicated (**p<0.01; ***p<0.001).</p

Electrophysiological properties of Ca_v3.1, Ca_v3.3, and their deletion mutants.

<p>The <i>G_max</i> and <i>V_0.5</i> of activation were determined from the <i>I-V</i> protocol, and therefore have the same number of cells (n) in each measurement. The <i>G/Q</i> ratio was calculated for each individual cell, and then averaged. Statistical significance is denoted with asterisks, where three asterisks indicates P<0.001, two for P<0.01, and one for P<0.05.</p

Estimating the effect of the deletions on the probability of channel opening.

<p><i>Aa</i>, Schematic of the P/-8 voltage protocol. <i>Ab</i>, Representative current at full scale, which is expanded in panel <i>Ac</i>. <i>B,C</i> Representative gating current traces recorded during depolarizing voltage steps from −100 to ∼ +50 mV (reversal potential): WT Ca_v3.1 (<i>Ba</i>); GD1–2 (<i>Bb</i>); GD3–5 (<i>Bc</i>); WT Ca_v3.3 (<i>Ca</i>); ID1–2 (<i>Cb</i>); and ID3–5 (<i>Cc</i>). Vertical scale bar is same size for all six traces (0.1 nA), while the horizontal scale bar is 1 ms in <i>B</i> and 2 ms in <i>C</i>. Data were acquired at 20 kHz, filtered at 10 kHz, and represent the average of 20 runs. G_max vs. Q_max for WT Ca_v3.1 and GD1–2 (<i>D</i>), or WT Ca_v3.3 and ID1–2 (<i>E</i>). The slope of the linear regression fit provides an estimate of <i>P_o,</i> and in both cases the slope of the line fitting the D1–2 mutants was 2-fold higher than for WT (Ca_v3.1, 0.26±0.03, n = 9; GD1–2, 0.55±0.06, n = 6, P<0.001; Ca_v3.3, 0.12±0.01, n = 9; and ID1–2, 0.26±0.02, n = 6, P<0.05). The difference between Ca_v3.1 and Ca_v3.3 is also statistically significant (P<0.001, one-way ANOVA followed by Tukey's multiple comparison test, Prism).</p

Effect of D1–2 deletions on kinetics of Ca_v3.1 and Ca_v3.3 kinetics.

<p><i>A</i>, <i>B,</i> Normalized current traces for Ca_v3.1 (thick gray line), Ca_v3.3 (dashed line), and ID1–2. Currents were recorded during step depolarizations to −10 mV. The same current traces are shown in <i>A</i> and <i>B</i>, but at a different time scale. In <i>A</i> the time scale is expanded to illustrate how ID1–2 activates as fast as Ca_v3.1, while in <i>B</i> a longer time scale is shown to illustrate how ID1–2 inactivates at a similar rate as WT Ca_v3.3. <i>C,</i> Average activation kinetics estimated using a 2 exponential fit to the raw current traces obtained during the <i>I-V</i> protocol. Data represent mean±s.e.m , and N is shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002976#pone-0002976-t001" target="_blank">Table 1</a>. <i>D,</i> Average inactivation kinetics. Same symbol definition as in panel <i>C</i>.</p

Location of deletions in the I–II loop.

<p>(<i>A</i>), Schematic representation of the I–II loop connecting repeat IS6 to repeat IIS1 in Ca_v3.1 and Ca_v3.3. Deleted regions are shown as open boxes. (<i>B</i>), Alignment of the I–II loop of human Ca_v3 channels. Arrows indicate where deletions begin and end. Dashes represent gaps in the alignment. Amino acids are color-coded by their physical properties as follows: red, positively-charged; green, negatively-charged; blue, polar; and yellow, hydrophobic.</p

Longitudinal telemetric monitoring of locomotor activity and body temperature in female mice.

<p>A. Daytime (open circles) and night-time (closed circles) counts in locomotion throughout a reproductive cycle. B. Average day-night amplitude in body temperature throughout a reproductive cycle. (mean±sem, n = 3 mice; temperature amplitudes were significantly smaller every days of lactation as compared to the period before mating, F(21, 42) = 9.333, p<0.0001 2-way ANOVA Tukey's multiple comparisons test). C and D. Representative example of 24-hour variations in body temperature, recorded in a same mouse before mating (C) and during lactation (D). ZT0 defined as time of lights on.</p

The circadian clockwork is preserved in the SCN of lactating mice.

<p>A. Expression profiles of circadian clock and clock-related genes in the SCN of virgin (black) and lactating (red) mice, as assessed by quantitative PCR (mean ± SEM, n = 4 samples for each time point. The sine lines represent the best cosinor fit for each dataset (see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187001#pone.0187001.t001" target="_blank">Table 1</a>) B. Representative micrographs (left panels) of immunostaining for PER2 in the SCN from virgin (top) and lactating (bottom) mice, at ZT 0 and ZT 12. The number of PER2-immunopositive cells per SCN was quantified over a complete daily cycle (right panel, mean ± SEM, n = 3 mice for each time point). A highly significant time effect was observed (p < 0.0001), with no difference between reproductive states (p = 0.12, two-way ANOVA). C. Representative recordings of PER2::LUC expression showing robust circadian oscillations in SCN slices from both virgin (left panel) and lactating (right panel) females. The time of occurrence of the circadian oscillation peak during the interval between 12 and 36 hours in culture, did not differ between both conditions (25.89±0.97 hrs, n = 8, and 24.87±0.45 hrs, n = 7, respectively, p = 0.17, unpaired t-test).</p

Modeling the regulation of SCN outputs by systemic feedback.

<p>A. Diagram depicting functional interactions entered into the mathematical model. B. The apparent free-running period of the locomotor rhythm (solid blue line) depends on the values of t and of the intrinsic period of the circadian clock. This example is constructed with numerical values published by Reinke et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187001#pone.0187001.ref031" target="_blank">31</a>], with the clock period set at 23.68 h (dotted red line). For an apparent period of 23.05 h, the value of t is 22.86 h (dotted black lines). The dotted blue line represents the line y = x. C. Predicted rhythmicity of the SCN electrical output when systemic feedback is suppressed, as in SCN slices. The reduced amplitude of the SCN output recapitulates dampened rhythms observed in lactating and <i>Hsf1-/-</i> mice [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187001#pone.0187001.ref035" target="_blank">35</a>]. D. The suppression of clock oscillations (red line) recapitulated the rebound-shape pattern of SCN firing (green arrow) and pre-dark locomotor behavior (blue arrow) observed in Cry1-/- Cry2-/- mice [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187001#pone.0187001.ref002" target="_blank">2</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187001#pone.0187001.ref036" target="_blank">36</a>]. E. Phase-dissociation between clock oscillations and overt rhythms after abrupt phase-shift of C, as in the case of a 6-hour advance of the light schedule [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187001#pone.0187001.ref037" target="_blank">37</a>]. (Red dots and blue lines represent the middle of the up-state of C and the onset of L, respectively.)</p

The daily rhythm in SCN electrical properties is suppressed in lactating mice.

<p>A-B. Cumulative distributions of membrane potentials measured in patch-clamped cells, from virgin (A) and lactating (B) mice. C-D. Cumulative distributions of extracellular single neuron firing frequencies, from virgin (C) and lactating (D) mice. SCN slices were recorded during either daytime (empty symbols) or night-time (filled symbols). The firing frequencies measured in patch-clamped cells are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187001#pone.0187001.s001" target="_blank">S1 Fig</a>. Differences were considered significant for p < 0.05, Kolmogorov-Smirnov test, n = 30 to 48 cells, from at least 5 different mice for each condition.</p