Figure 1.
Schematic of signalling in ASMC.
Agonist stimulation of G-protein coupled receptors (GPCR) induces PLC activation, giving rise to
production and
entry through receptor-operated
channels (ROCC).
triggers
release through IPR. Depletion of the SR from
causes STIM protein oligomerisation and migration toward the cell membrane, where they bind and activate store-operated
channels (SOCC).
ATP-ases pump
back into the SR (SERCA) and out of the cell (PMCA).
Figure 2.
Fluorescence image of part of a mouse airway wall obtained by two-photon laser scanning microscopy.
The yellow square shows a typical region, within an ASMC, from which dynamics is imaged.
Table 1.
Parameter values used in the model.
Figure 3.
dynamics in ASMC: experiment and model.
(A)–(C): Fluorescence imaging of dynamics in an ASMC within a human lung slice, during the following 3-step experiment: (A) Agonist stimulation, (B) Rya-Caf treatment, and (C) second agonist stimulation. Following the irreversible Rya-Caf treatment in (B), agonist stimulation (C) is no longer able to elicit
oscillations, nor does it perturb the new elevated
equilibrium. Reprinted from [2] under a CC BY license, with permission of the American Thoracic Society, original copyright 2010. Cite: Ressmeyer et al. /2010/Am J Respir Cell Mol Biol/43/179–191. Official journal of the American Thoracic Society. This modified figure is based on the original figure available from www.atsjournals.org. (D)–(F): Simulations of the experiments in (A)–(C) using Eqs. 114–12 and the parameter values in Table 1. The evolution of
,
, and
(fraction of open SOCC) are shown (cf. legend in (E)).
Figure 4.
dynamics as a function of agonist concentration.
Dashed curves represent steady-states (constant levels); solid curves, periodic solutions (
oscillations). The maximum
(black) and the maximum fraction of open SOCC (blue) during one solution period are plotted as ordinates. The red curve (right y-axis) shows the frequency of the
oscillations on the main stable segment (from the upper blue dot to the black cross), which fits the experimental range in human [2]. The stable solutions are represented as thick lines and unstable solutions as thin lines. The green diamonds represent Hopf bifurcations, the black cross, a saddle-node bifurcation, and the blue dots, period-doubling points. Period-doubled branches are not shown because they extend only over a tiny range of
values; moreover it is likely that the deterministic description of
oscillations fails at these low agonist concentrations (see Discussion). The vertical dotted line indicates the value of
used in Fig. 3 (Table 1).
Figure 5.
Influence of SOCE on agonist-induced oscillations.
Amplitude (black) and frequency (red) of oscillations as a function of (A) SOCE maximum rate,
, and (B) STIM affinity for SR
,
. Dotted lines indicate the “normal” parameter values (Table 1, Figs. 3D–F). As in Fig. 4, only the frequency of the large-amplitude stable
oscillations is shown.
Figure 6.
(A) Fluorescence imaging of in ASMC of a mouse lung slice treated with agonist and CPA. Agonist removal leads to
decrease. (B–D) Model simulations of the experiments shown in (A), assuming that (B) CPA quickly blocks the SERCA, (C) CPA slowly blocks the SERCA, (D) CPA partially blocks the SERCA but reaches maximum strength rather quickly. Black solid and dashed curves (left y-axis) represent respectively
and
; blue and red curves (right y-axis) show respectively the fraction of open SOCC and the fraction of operating SERCA (that is,
, where
is given by Eq. (0c)).
Figure 7.
Experimental evidence that CPA does not fully empty the SR of ASMC.
Tests of the model predictions shown in Fig. 6B–D, performed with mouse lung slices. (A) Significantly longer exposure to agonist+CPA and to CPA than in Fig. 6A still fails to maintain SOCE. (B) Same experiment as in (A) except that extracellular is removed before agonist is applied a second time, confirming the residual presence of
in the SR and hence the partial efficacy of CPA to inhibit SERCA (scenario of Fig. 6D). (Insets show magnifications of selected time windows).