Modelling the electrophysiological endothelial cell response to bradykinin

The goal of the present study is to construct a biophysical model of the coronary artery endothelial cell response to bradykinin. This model takes into account intracellular Ca2+ dynamics, membrane potential, a non-selective cation channel, and two Ca2+-dependent K+ channels, as well as intra- and extracellular Ca2+ sources. The model reproduces the experimental data available, and predicts certain quantities which would be hard to obtain experimentally, like the individual K+ channel currents when the membrane potential is allowed to freely evolve, the implication of epoxyeicosatrienoic acids (EETs), and the total K+ released during stimulation. The main results are: (1) the large-conductance K+ channel participates only very little in the overall response; (2) EETs are required in order to explain the experimental current-potential relationships, but are not an essential component of the bradykinin response; and (3) the total K+ released during stimulation gives rise to a concentration in the intercellular space which is of millimolar order. This concentration change is compatible with the hypothesis that K+ contributes to the endothelium-derived hyperpolarizing factor phenomeno

Emergent properties of electrically coupled smooth muscle cells

Asynchronous and synchronous calcium oscillations occur in a variety of cells. A well-established pathway for intercellular communication is provided by gap junctions which connect adjacent cells and can mediate electrical and chemical coupling. Several experimental studies report that cells presenting only a transient increase when freshly dispersed may oscillate when they are coupled. Such observations suggest that the role of gap junctions is not only to coordinate calcium oscillations of adjacent cells. Gap junctions may also be important to generate oscillations. Here we illustrate the emergent properties of electrically coupled smooth muscle cells using a model that we recently proposed. A bifurcation analysis in the case of two cells reveals that synchronous and asynchronous calcium oscillations can be induced by electrical coupling. In a larger population of smooth muscle cells, electrical coupling may result in the creation of groups of cells presenting synchronous calcium oscillations. The elements of one group may be distant from each other. Moreover, our results highlight a general mechanism by which gap junctional electrical coupling can give rise to out of phase calcium oscillations in smooth muscle cells that are non-oscillating when uncoupled. All these observations remain true in the case of non-identical cells, except that the solution corresponding to synchronous calcium oscillations disappears and that the formation of groups is sensitive to the degree of heterogeneit

A minimal model for spontaneous cell polarization and edge activity in oscillating, rotating and migrating cells

How the cells break symmetry and organize their edge activity to move directionally is a fun- damental question in cell biology. Physical models of cell motility commonly rely on gradients of regulatory factors and/or feedback from the motion itself to describe polarization of edge activity. Theses approaches, however, fail to explain cell behavior prior to the onset of polarization. Our analysis using the model system of polarizing and moving fish epidermal keratocytes suggests a novel and simple principle of self-organization of cell activity in which local cell-edge dynamics depends on the distance from the cell center, but not on the orientation with respect to the front-back axis. We validate this principle with a stochastic model that faithfully reproduces a range of cell-migration behaviors. Our findings indicate that spontaneous polarization, persistent motion, and cell shape are emergent properties of the local cell-edge dynamics controlled by the distance from the cell center.Comment: 8 pages, 5 figure

Identification and functional response of interstitial Cajal-like cells from rat mesenteric artery

Cells with irregular shapes, numerous long thin filaments, and morphological similarities to the gastrointestinal interstitial cells of Cajal (ICCs) have been observed in the wall of some blood vessels. These ICC-like cells (ICC-LCs) do not correspond to the other cell types present in the arterial wall: smooth muscle cells (SMCs), endothelial cells, fibroblasts, inflammatory cells, or pericytes. However, no clear physiological role has as yet been determined for ICC-LCs in the vascular wall. The aim of this study has been to identify and characterize the functional response of ICC-LCs in rat mesenteric arteries. We have observed ICC-LCs and identified them morphologically and histologically in three different environments: isolated artery, freshly dispersed cells, and primary-cultured cells from the arterial wall. Like ICCs but unlike SMCs, ICC-LCs are positively stained by methylene blue. Cells morphologically resembling methylene-blue-positive cells are also positive for the ICC and ICC-LC markers α-smooth muscle actin and desmin. Furthermore, the higher expression of vimentin in ICC-LCs compared with SMCs allows a clear discrimination between these two cell types. At the functional level, the differences observed in the variations of cytosolic free calcium concentration of freshly dispersed SMCs and ICC-LCs in response to a panel of vasoactive molecules show that ICC-LCs, unlike SMCs, do not respond to exogenous ATP and [Arginine]8-vasopressi

Modelling the electrophysiological endothelial cell response to bradykinin

The goal of the present study is to construct a biophysical model of the coronary artery endothelial cell response to bradykinin. This model takes into account intracellular Ca2+ dynamics, membrane potential, a non-selective cation channel, and two Ca(2+)-dependent K+ channels, as well as intra- and extracellular Ca2+ sources. The model reproduces the experimental data available, and predicts certain quantities which would be hard to obtain experimentally, like the individual K+ channel currents when the membrane potential is allowed to freely evolve, the implication of epoxyeicosatrienoic acids (EETs), and the total K+ released during stimulation. The main results are: (1) the large-conductance K+ channel participates only very little in the overall response; (2) EETs are required in order to explain the experimental current-potential relationships, but are not an essential component of the bradykinin response; and (3) the total K+ released during stimulation gives rise to a concentration in the intercellular space which is of millimolar order. This concentration change is compatible with the hypothesis that K+ contributes to the endothelium-derived hyperpolarizing factor phenomenon

Weak Force Stalls Protrusion at the Leading Edge of the Lamellipodium

AbstractProtrusion, the first step of cell migration, is driven by actin polymerization coupled to adhesion at the cell’s leading edge. Polymerization and adhesive forces have been estimated, but the net protrusion force has not been measured accurately. We arrest the leading edge of a moving fish keratocyte with a hydrodynamic load generated by a fluid flow from a micropipette. The flow arrests protrusion locally as the cell approaches the pipette, causing an arc-shaped indentation and upward folding of the leading edge. The effect of the flow is reversible upon pipette removal and dependent on the flow direction, suggesting that it is a direct effect of the external force rather than a regulated cellular response. Modeling of the fluid flow gives a surprisingly low value for the arresting force of just a few piconewtons per micrometer. Enhanced phase contrast, fluorescence, and interference reflection microscopy suggest that the flow does not abolish actin polymerization and does not disrupt the adhesions formed before the arrest but rather interferes with weak nascent adhesions at the very front of the cell. We conclude that a weak external force is sufficient to reorient the growing actin network at the leading edge and to stall the protrusion

Focal adhesion size controls tension-dependent recruitment of α-smooth muscle actin to stress fibers

Expression of α-smooth muscle actin (α-SMA) renders fibroblasts highly contractile and hallmarks myofibroblast differentiation. We identify α-SMA as a mechanosensitive protein that is recruited to stress fibers under high tension. Generation of this threshold tension requires the anchoring of stress fibers at sites of 8–30-μm-long “supermature” focal adhesions (suFAs), which exert a stress approximately fourfold higher (∼12 nN/μm2) on micropatterned deformable substrates than 2–6-μm-long classical FAs. Inhibition of suFA formation by growing myofibroblasts on substrates with a compliance of ≤11 kPa and on rigid micropatterns of 6-μm-long classical FA islets confines α-SMA to the cytosol. Reincorporation of α-SMA into stress fibers is established by stretching 6-μm-long classical FAs to 8.1-μm-long suFA islets on extendable membranes; the same stretch producing 5.4-μm-long classical FAs from initially 4-μm-long islets is without effect. We propose that the different molecular composition and higher phosphorylation of FAs on supermature islets, compared with FAs on classical islets, accounts for higher stress resistance

Identification and functional response of interstitial Cajal-like cells from rat mesenteric artery

Cells with irregular shapes, numerous long thin filaments, and morphological similarities to the gastrointestinal interstitial cells of Cajal (ICCs) have been observed in the wall of some blood vessels. These ICC-like cells (ICC-LCs) do not correspond to the other cell types present in the arterial wall: smooth muscle cells (SMCs), endothelial cells, fibroblasts, inflammatory cells, or pericytes. However, no clear physiological role has as yet been determined for ICC-LCs in the vascular wall. The aim of this study has been to identify and characterize the functional response of ICC-LCs in rat mesenteric arteries. We have observed ICC-LCs and identified them morphologically and histologically in three different environments: isolated artery, freshly dispersed cells, and primary-cultured cells from the arterial wall. Like ICCs but unlike SMCs, ICC-LCs are positively stained by methylene blue. Cells morphologically resembling methylene-blue-positive cells are also positive for the ICC and ICC-LC markers alpha-smooth muscle actin and desmin. Furthermore, the higher expression of vimentin in ICC-LCs compared with SMCs allows a clear discrimination between these two cell types. At the functional level, the differences observed in the variations of cytosolic free calcium concentration of freshly dispersed SMCs and ICC-LCs in response to a panel of vasoactive molecules show that ICC-LCs, unlike SMCs, do not respond to exogenous ATP and [Arginine](8)-vasopressin