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

Information Networks in the Arterial Wall

The main task of the arterial system is to secure an adequate supply of oxygen to organs. This fact implies the integration of multiple signals in the vascular wall. This review deals with the exchange of information between and among smooth muscle and endothelial cells through gap junctions in the vessel walls of arteries and arterioles.</p

Characterization of purine receptors in mouse thoracic aorta

The contracting and relaxing effects of purines and UTP were investigated on rings of mouse thoracic aorta in vitro. UTP, ATPγS, and α-β-Methyleneadenosine 5' triphosphate contracted rings with and without endothelium. On the contrary, adenosine, AMP, ADP, ATP, and 2-(methylthio) adenosine 5'-diphosphate had no effect on relaxed rings. When rings were tonically contracted by U46619 a thromboxane A2 analogue, ATP, ADP, ATPγS, 2-(methylthio) adenosine 5'-diphosphate, and UTP caused endothelium-dependent but not independent relaxations. I conclude that ATP acts on P2Y2 and P2Y1 receptors on the endothelial cells to cause endothelium-dependent relaxation. In this tissue, the relaxing effect of ATP dominates by endothelium-dependent ways when aorta rings are contracted by a stable thromboxane A2 analog. However receptors mediating contraction in response to purines and pyrimidines are present on smooth muscle cells. Indeed, the stimulation of P2Y receptors by UTP as well as the activation of P2X family receptors by ATPγS causes a contraction. The potential contractile effect of ATP seems masked by its hydrolysis by ectonucleotidases

The role of the sodium-calcium exchanger for calcium extrusion in coronary arteries

Calcium ionophores, such as the A23187, cause endothelium-dependent relaxation of arterial strips with intact endothelium, whereas the effect of the ionophore should result from the combination of a relaxation caused by the endothelium-dependent factors and of a contraction of the smooth muscles. In addition, the application of a calcium ionophore to a strip of pig coronary arteries without endothelium does not change cytosolic free calcium concentration and force developed by the smooth muscle cells. To explain these paradoxes, the hypothesis that active calcium extrusion would match the entry of extracellular calcium caused by the ionophore was tested. We see that the sodium-calcium exchanger extrudes calcium that enters the smooth muscle cells in the absence of the ionophore. This exchanger is efficient enough to expel the increased influx of calcium created by the additional calcium carriers formed by the ionophore. This explains the inefficiency of calcium ionophores to increase cytosolic free calcium of smooth muscle cells and consequently, the fact that the ionophore does not cause a contraction of a strip without endothelium. This makes evident that a calcium ionophore fully relaxes, in an endothelium-dependent manner, an intact strip of porcine coronary artery

Endothelium-Dependent Hyperpolarization Cannot Be Explained by Electrical Coupling Between the Endothelial and the Smooth Muscle Cells in Muscular Arteries

In the porcine coronary artery, endothelium-derived hyperpolarizing factor (EDHF) is responsible for 70% of the endothelium-dependent vasodilatation caused by bradykinin. This relaxation is associated with the simultaneous hyperpolarization of endothelial and smooth muscle cells. The synchronism of these two hyperpolarizations suggests that an electrical communication between the endothelial and smooth muscle cells may underly endothelium dependent hyperpolarizations of vascular smooth muscle, a phenomenon that has been attributed to EDHF. By contrast, in the porcine ciliary artery, EDHF is not implicated in the bradykinin-evoked endothelium-dependent relaxations. Experiments were designed to compare the behavior of arteries with and without EDHF-mediated responses. In a strip of ciliary artery incubated in vitro, dye coupling experiments demonstrated heterocellular coupling between the endothelial and smooth muscle cells. In addition, a 12 mV transient bradykinin-induced hyperpolarization was measured using microelectrodes in endothelial cells. Nevertheless, bradykinin evoked no hyperpolarization of smooth muscle cells in this artery, although a 4 mV hyperpolarization could be recorded in a few smooth muscle cells next to the endothelium. These observations are compatible with the concept that in arteries where the EDHF-component is absent, the current which causes the hyperpolarization of the endothelial cell is not strong enough to passively change the membrane potential of the coupled multiple layers of smooth muscle cells. As a corollary, a phenomenon other than passive electrical coupling alone must be responsible for the transmission of the hyperpolarization of the endothelial cells to the smooth muscle cells in aneries where endothelium-dependent hyperpolarizations occur

Calcium Imaging of Murine Thoracic Aorta Endothelium by Confocal Microscopy Reveals Inhomogeneous Distribution of Endothelial Cells Responding to Vasodilator Agents

The aim of the study was to assess, in intact murine thoracic aorta in vitro, the distribution of endothelial cells responsive to endothelium-dependent vasodilators ACh, ATP, bradykinin and substance P, using laser line confocal microscopy in combination with two Ca&lt;sup&gt;2+&lt;/sup&gt; fluorescent dyes, Fluo-4 and Fura-red. We observed that 82 ± 3% of endothelial cells responded to ATP, 33 ± 5% to Ach, whereas less than 3% of them responded to bradykinin or substance P. In order to determine whether the findings of pharmacological tests agree with confocal microscopy data, endothelium-dependent vasodilators induced relaxation was evaluated using isometric tension measurement. We show a marked correlation between a higher number of activated endothelial cells, using confocal microscopy, and a greater degree of endothelium-dependent relaxation using isometric tension measurement (p = 0.00286). Our results suggest that endothelial cells responding to endothelium-dependent vasodilators are not homogeneously distributed in intact murine thoracic aorta. This could be due to nonhomogeneous distribution of surface receptors or to differences in post-receptor coupling mechanisms.</p

Kinins and Endothelium-Dependent Hyperpolarization in Porcine Coronary Arteries

The endothelial and the vascular smooth muscle cells of an arterial strip of coronary artery of the pig are not dye-coupled. However, substance P and bradykinin induce an hyperpolarization of the endothelial cells and, simultaneously, an endothelium-dependent relaxation and hyperpolarization of the smooth muscle cells. Therefore the question arises about a possible causality between these two hyperpolarizations. To answer this question, the hypothesis that the endothelial cells are coupled electrically by gap junctions to the underlying smooth muscle cells was tested by observing whether or not changes in membrane potentials that occur in the smooth muscle cells would be transmitted to the endothelial cells. Hyperpolarization caused to smooth muscle cells by a beta-adrenergic agonist, and action potentials generated in these cells by a blocker of potassium channels were transmitted to the adjoining endothelial cells. These observations suggest a heterologous cell electrical coupling. Halothane, a molecule known to uncouple cells linked by gap junctions, inhibited the transmission of electrical signals from the smooth muscle to the endothelial cells, but did not inhibit the propagation of hyperpolarization caused by substance P and bradykinin from the endothelium to the smooth muscle cells. These observations suggest the existence of an asymetric barrier to the movement of ions by heterologous coupling in the arterial wall. They strengthen the concept that endothelium-dependent hyperpolarizing factor is a chemical messenger. It remains to explain how a paracrine factor can faithfully reproduce in the smooth muscle cells hyperpolarizations that are generated in the endothelium in response to kinins

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

Electrotonic Propagation of Kinin-Induced, Endothelium-Dependent Hyperpolarizations in Pig Coronary Smooth Muscles

The kinins, substance P and bradykinin, cause endothelium-dependent hyperpolarizations in smooth muscles of the pig coronary artery. We tested whether the propagation, in the media, of these hyperpolarizations is passive or whether the hyperpolarizations are regenerated in the smooth muscle cells. The space constants measured in response to the kinin endothelium-dependent stimulations were compared to those obtained by electrical field stimulation. The space constant is 2.6 ± 0.2 mm (n = 13) measured for substance P and 2.2 ± 0.2 mm (n = 12) for bradykinin. The space constants established by electrical field stimulation-induced hyperpolarization are 3 ± 0.2 mm (n = 7) for strips with intact endothelium and 2.7 ± 0.3 mm (n = 7) for strips with removed endothelium. These results show that the space constants obtained for the kinin stimulations are not larger than those caused by electrical field stimulation. This suggests that the kinin-induced hyperpolarizations propagate, in the media, in a passive, electronic manner, therefore the hypothesis of regenerated kinin hyperpolarizations is unlikely