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Results: 11

1.
FIGURE 10

FIGURE 10. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

The predicted effect of the MLCK level on the amplitude of the phosphorylated MLC concentration during cortical oscillations.

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.
2.
FIGURE 11

FIGURE 11. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

Predicted effects of PMCA activity on the phosphorylated MLC and free calcium concentrations: Vpmca = 0.5 mM/s (top panels), Vpmca = 2.0 mM/s (middle panels), and Vpmca = 20 mM/s (bottom panels).

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.
3.
FIGURE 6

FIGURE 6. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

One period of the oscillatory behavior. Graphs ad demonstrate the temporal relationship between changes in membrane area, SAC current, [Ca2+], and contractility (see text for details).

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.
4.
FIGURE 4

FIGURE 4. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

Schematic diagram of the biochemical pathway involving Ca2+, calmodulin, and MLCK. The model considers all possible reactions for the binding of pairs of calcium ions to the C- and N-terminals of calmodulin. The model also allows binding between MLCK and CaM with a single pair of calcium ions.

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.
5.
FIGURE 5

FIGURE 5. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

Time-series showing oscillations in the concentrations of Ca2+ ions (solid line) and phosphorylated MLC (dashed line). The results represent numerical simulations of the model equations (see Appendix) using the basic set of parameter values (Table 1) and [MLCP] = 1 μM, Kcyt = 25 μm/s; Kcont = 2 μm μM−1 s−1.

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.
6.
FIGURE 9

FIGURE 9. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

The system's sensitivity to variations in selected model parameter values. The sensitivity coefficients were evaluated using the basic values listed in Table 1 both for [MLCP] = 2 μM, where the oscillation amplitude is a maximum, and [MLCP] = 1 μM, which corresponds to 65% of maximum amplitude. The sensitivity coefficients for changes in the period and amplitude were calculated using ±10% and ±30% variations in each of the model parameters.

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.
7.
FIGURE 8

FIGURE 8. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

Contour plots (a and b) and selected cross sections (c and d) of the oscillation period and amplitude as a function of Kcyt and MLCP. When Kcyt is between 20 and 50 μm/s, oscillations occur over a range of MLCP concentrations from 1 to 6 mM. The maximum amplitude occurs near MLCP = 2 μM and Kcyt = 25–30 μm/s. Smaller concentrations of MLCP produce longer oscillation periods.

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.
8.
FIGURE 7

FIGURE 7. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

A single parameter bifurcation diagram for Kcyt with the MLC phosphatase concentration fixed at 2 μM. The values of Kcyt labeled B1 and B2 are the bifurcation points. Between B1 and B2, oscillations occur (inset b). In this region, the two curves shown in the figure represent the maximum and minimum values achieved by the concentration during the oscillations. If Kcyt < B1, only damped oscillations are produced (inset a). Eventually Kcyt becomes sufficiently large (>B2) to overcome myosin-based contractility abolishing oscillations (inset c).

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.
9.
FIGURE 3

FIGURE 3. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

Schematic diagram for the mechanism of cortical oscillations. Oscillations are initiated by a local expansion of the membrane that results from increased cytosolic pressure after microtubule depolymerization. This local extension produces a calcium influx via stretch-activated channels (SAC), which increases the calcium concentration in cytosol. The increased calcium levels stimulate actomyosin contractility via the calmodulin (CaM)-MLCK pathway. The increased contractility retracts the membrane and closes the SACs, thus providing a negative feedback loop. Removal of calcium via calcium pumps leads to a decrease in contractility allowing another cycle to begin.

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.
10.
FIGURE 2

FIGURE 2. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

(Panel 1) Microtubule depolymerization produces a nonuniform increase in contractility resulting in a local protrusion of the cell membrane. The extension of region A activates mechanosensitive channels in the plasma membrane and produces a calcium influx, which in turn stimulates actomyosin contractility. (Panels 2 and 3) The additional contractility tends to force cytosol into region B, thereby reducing the membrane extension and closing the mechanosensitive calcium channels. This leads to a decrease in intracellular calcium levels and an eventual reduction in contractility (negative feedback). (Panel 4) Region B expands sufficiently to initiate another round of calcium-induced contractility, and the process repeats.

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.
11.
FIGURE 1

FIGURE 1. From: Mechanical and Biochemical Modeling of Cortical Oscillations in Spreading Cells.

Time dependence of the phase contrast brightness intensity for a single cell after microtubule depolymerization. (a) The relative brightness of opposite regions of the cell was determined from images recorded at 10 s intervals. The data represent an average of the intensities measured within the cellular regions shown in the first panel of b. To produce these time series, the background intensity was subtracted and the resulting time-series normalized to have a maximum of 1. The time courses begin 48 min after plating. The oscillation period for this cell is ∼50 s. The time-series demonstrate that opposite ends of cell contract out-of-phase. (b) Selected images corresponding to the time points shown in a. The first panel shows the regions from which the intensity measurements were made. Each image represents a time point at which one of the two regions is at a maximum as indicated by the white arrows. The bar in the last panel represents 20 μm.

Maryna Kapustina, et al. Biophys J. 2008 June 15;94(12):4605-4620.

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