RESUMEN
In rat mesenteric arteries, smooth muscle cells exhibit intercellular calcium waves in response to local phenylephrine stimulation. These waves have a velocity of approximately 20 cells/s and a range of approximately 80 cells. We analyze these waves in a theoretical model of a population of coupled smooth muscle cells, based on the hypothesis that the wave results from cell membrane depolarization propagation. We study the underlying mechanisms and highlight the importance of voltage-operated channels, calcium-induced calcium release, and chloride channels. Our model is in agreement with experimental observations, and we demonstrate that calcium waves presenting a velocity of approximately 20 cells/s can be mediated by electrical coupling. The wave velocity is limited by the time needed for calcium influx through voltage-operated calcium channels and the subsequent calcium-induced calcium release, and not by the speed of the depolarization spreading. The waves are partially regenerated, but have a spatial limit in propagation. Moreover, the model predicts that a refractory period of calcium signaling may significantly affect the wave appearance.
Asunto(s)
Señalización del Calcio , Calcio/metabolismo , Espacio Extracelular/metabolismo , Arterias Mesentéricas/citología , Miocitos del Músculo Liso/metabolismo , Animales , Canales de Cloruro/metabolismo , Conductividad Eléctrica , Activación del Canal Iónico , Modelos Biológicos , RatasRESUMEN
Vasomotion consists of cyclic arterial diameter variations induced by synchronous contractions and relaxations of smooth muscle cells. However, the arteries do not contract simultaneously on macroscopic distances, and a propagation of the contraction can be observed. In the present study, our aim was to investigate this propagation. We stimulated endothelium-denuded rat mesenteric arterial strips with phenylephrine (PE) to obtain vasomotion and observed that the contraction waves are linked to intercellular calcium waves. A velocity of approximately 100 microm/s was measured for the two kinds of waves. To investigate the calcium wave propagation mechanisms, we used a method allowing a PE stimulation of a small area of the strip. No calcium propagation could be induced by this local stimulation when the strip was in its resting state. However, if a low PE concentration was added on the whole strip, local PE stimulations induced calcium waves, spreading over finite distances. The calcium wave velocity induced by local stimulation was identical to the velocity observed during vasomotion. This suggests that the propagation mechanisms are similar in the two cases. Using inhibitors of gap junctions and of voltage-operated calcium channels, we showed that the locally induced calcium propagation likely depends on the propagation of the smooth muscle cell depolarization. Finally, we proposed a model of the propagation mechanisms underlying these intercellular calcium waves.
Asunto(s)
Calcio/metabolismo , Arterias Mesentéricas/fisiología , Vasoconstricción/fisiología , Animales , Canales de Calcio/metabolismo , Uniones Comunicantes/metabolismo , Masculino , Arterias Mesentéricas/efectos de los fármacos , Modelos Animales , Fenilefrina/farmacología , Ratas , Ratas Wistar , Vasoconstricción/efectos de los fármacos , Vasoconstrictores/farmacologíaRESUMEN
In vitro, different techniques are used to study the smooth muscle cells' calcium dynamics and contraction/relaxation mechanisms on arteries. Most experimental studies use either an isometric or an isobaric setup. However, in vivo, a blood vessel is neither isobaric nor isometric nor isotonic, as it is continuously submitted to intraluminal pressure variations arising from heart beat. We use a theoretical model of the smooth muscle calcium and arterial radius dynamics to determine whether results may be considerably different depending on the experimental conditions (isometric, isobaric, isotonic, or cyclic pressure variations). We show that isobaric conditions appear to be more realistic than isometric or isotonic situations, as the calcium dynamics is similar under cyclic intraluminal pressure variations (in vivo-like situation) and under a constant pressure (isobaric situation). The arterial contraction is less pronounced in isotonic than in isobaric conditions, and the vasoconstrictor sensitivity higher in isometric than isobaric or isotonic conditions, in agreement with experimental observations. Interestingly, the model predicts that isometric conditions may generate artifacts like the coexistence of multiple stable states. We have verified this model prediction experimentally using rat mesenteric arteries mounted on a wire myograph and stimulated with phenylephrine.
Asunto(s)
Arterias/metabolismo , Arterias/fisiología , Calcio/metabolismo , Contracción Isométrica , Contracción Isotónica , Movimiento , Animales , Arterias/efectos de los fármacos , Contracción Isométrica/efectos de los fármacos , Contracción Isotónica/efectos de los fármacos , Masculino , Arterias Mesentéricas/efectos de los fármacos , Arterias Mesentéricas/metabolismo , Arterias Mesentéricas/fisiología , Modelos Biológicos , Movimiento/efectos de los fármacos , Miocitos del Músculo Liso/metabolismo , Miografía , Fenilefrina/metabolismo , Presión , Ratas , Reproducibilidad de los Resultados , Vasoconstrictores/farmacologíaRESUMEN
BACKGROUND AND AIMS: Vasomotion consists in cyclic oscillations of the arterial diameter induced by the synchronized activity of the smooth muscle cells. So far, contradictory results have emerged in the literature about the role of the endothelium in the onset and maintenance of vasomotion. Here our aim is to understand how the endothelium may either abolish or promote vasomotion. METHODS AND RESULTS: We investigate rat mesenteric arterial strips stimulated with phenylephrine (PE). Our results show that the endothelium is not necessary for vasomotion. However, when the endothelium is removed, the PE concentration needed to induce vasomotion is lower and the rhythmic contractions occur for a narrower range of PE concentrations. We demonstrate that endothelium-derived relaxing products may either induce or abolish vasomotion. On the one hand, when the strip is tonically contracted in a nonoscillating state, an endothelium-derived relaxation may induce vasomotion. On the other hand, if the strip displays vasomotion with a medium mean contraction, a relaxation may induce a transition to a nonoscillating state with a small contraction. CONCLUSION: Our findings clarify the role of the endothelium on vasomotion and reconcile the seemingly contradictory observations reported in the literature.
Asunto(s)
Endotelio Vascular/metabolismo , Factores Relajantes Endotelio-Dependientes/metabolismo , Músculo Liso Vascular/metabolismo , Vasoconstricción , Animales , Apamina/farmacología , Relación Dosis-Respuesta a Droga , Endotelio Vascular/efectos de los fármacos , Endotelio Vascular/enzimología , Inhibidores Enzimáticos/farmacología , Técnicas In Vitro , Masculino , Arterias Mesentéricas/metabolismo , Músculo Liso Vascular/efectos de los fármacos , NG-Nitroarginina Metil Éster/farmacología , Óxido Nítrico/metabolismo , Donantes de Óxido Nítrico/farmacología , Óxido Nítrico Sintasa/antagonistas & inhibidores , Óxido Nítrico Sintasa/metabolismo , Nitroprusiato/farmacología , Periodicidad , Fenilefrina/farmacología , Bloqueadores de los Canales de Potasio/farmacología , Ratas , Ratas Wistar , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/antagonistas & inhibidores , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/metabolismo , Vasoconstricción/efectos de los fármacos , Vasoconstrictores/farmacologíaAsunto(s)
Arterias/fisiología , Comunicación Celular/fisiología , Endotelio Vascular/metabolismo , Músculo Liso Vascular/metabolismo , Sistema Vasomotor/fisiología , Animales , Arterias/citología , Arterias/ultraestructura , Factores Biológicos/fisiología , Señalización del Calcio , Corteza Cerebral/irrigación sanguínea , Corteza Cerebral/ultraestructura , Conexinas/metabolismo , Conexinas/ultraestructura , Endotelio Vascular/citología , Endotelio Vascular/ultraestructura , Inhibidores Enzimáticos/farmacología , Uniones Comunicantes/ultraestructura , Masculino , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Modelos Cardiovasculares , Músculo Liso Vascular/citología , Músculo Liso Vascular/ultraestructura , NG-Nitroarginina Metil Éster/farmacología , Óxido Nítrico Sintasa/antagonistas & inhibidores , Ratas , Ratas Wistar , Sistema Vasomotor/ultraestructura , Proteína alfa-5 de Unión Comunicante , Proteína alfa-4 de Unión ComunicanteRESUMEN
Smooth muscle and endothelial cells in the arterial wall are exposed to mechanical stress. Indeed blood flow induces intraluminal pressure variations and shear stress. An increase in pressure may induce a vessel contraction, a phenomenon known as the myogenic response. Many muscular vessels present vasomotion, i.e., rhythmic diameter oscillations caused by synchronous cytosolic calcium oscillations of the smooth muscle cells. Vasomotion has been shown to be modulated by pressure changes. To get a better understanding of the effect of stress and in particular pressure on vasomotion, we propose a model of a blood vessel describing the calcium dynamics in a coupled population of smooth muscle cells and endothelial cells and the consequent vessel diameter variations. We show that a rise in pressure increases the calcium concentration. This may either induce or abolish vasomotion, or increase its frequency depending on the initial conditions. In our model the myogenic response is less pronounced for large arteries than for small arteries and occurs at higher values of pressure if the wall thickness is increased. Our results are in agreement with experimental observations concerning a broad range of vessels.
Asunto(s)
Arterias/fisiología , Canales de Calcio/fisiología , Señalización del Calcio/fisiología , Calcio/metabolismo , Modelos Cardiovasculares , Contracción Muscular/fisiología , Sistema Vasomotor/fisiología , Animales , Células Cultivadas , Simulación por Computador , Elasticidad , Células Epiteliales/fisiología , Humanos , Activación del Canal Iónico/fisiología , Mecanotransducción Celular/fisiología , Potenciales de la Membrana/fisiología , Miocitos del Músculo Liso/fisiología , Estrés Mecánico , Vasoconstricción/fisiología , Vasodilatación/fisiologíaRESUMEN
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 heterogeneity.
Asunto(s)
Calcio/fisiología , Modelos Biológicos , Músculo Liso/fisiología , Relojes Biológicos/fisiología , Uniones Comunicantes/fisiología , Potenciales de la Membrana/fisiología , Músculo Liso/citología , Miocitos del Músculo Liso/fisiologíaRESUMEN
We investigated heterocellular communication in rat mesenteric arterial strips at the cellular level using confocal microscopy. To visualize Ca(2+) changes in different cell populations, smooth muscle cells (SMCs) were loaded with Fluo-4 and endothelial cells (ECs) with Fura red. SMC contraction was stimulated using high K(+) solution and Phenylephrine. Depending on vasoconstrictor concentration, intracellular Ca(2+) concentration ([Ca(2+)](i)) increased in a subpopulation of ECs 5-11s after a [Ca(2+)](i) rise was observed in adjacent SMCs. This time interval suggests chemical coupling between SMCs and ECs via gap junctions. As potential chemical mediators we investigated Ca(2+) or inositol 1,4,5-trisphosphate (IP(3)). First, phospholipase C inhibitor U-73122 was added to prevent IP(3) production in response to the [Ca(2+)](i) increase in SMCs. In high K(+) solution, all SMCs presented global and synchronous [Ca(2+)](i) increase, but no [Ca(2+)](i) variations were detected in ECs. Second, 2-aminoethoxydiphenylborate, an inhibitor of IP(3)-induced Ca(2+) release, reduced the number of flashing ECs by 75+/-3% (n = 6). The number of flashing ECs was similarly reduced by adding the gap junction uncoupler palmitoleic acid. Thus, our results suggest a heterocellular communication through gap junctions from SMCs to ECs by diffusion, probably of IP(3).
Asunto(s)
Señalización del Calcio/fisiología , Células Endoteliales/fisiología , Uniones Comunicantes/fisiología , Músculo Liso Vascular/fisiología , Sistemas de Mensajero Secundario/fisiología , Animales , Compuestos de Boro/farmacología , Calcio/metabolismo , Señalización del Calcio/efectos de los fármacos , Inhibidores Enzimáticos/farmacología , Estrenos/farmacología , Ácidos Grasos Monoinsaturados/farmacología , Fura-2/análogos & derivados , Uniones Comunicantes/efectos de los fármacos , Inositol 1,4,5-Trifosfato/fisiología , Masculino , Arterias Mesentéricas/fisiología , Fenilefrina/farmacología , Pirrolidinonas/farmacología , Ratas , Ratas Wistar , Fosfolipasas de Tipo C/antagonistas & inhibidoresRESUMEN
It is well-known that cyclic variations of the vascular diameter, a phenomenon called vasomotion, are induced by synchronous calcium oscillations of smooth muscle cells (SMCs). However, the role of the endothelium on vasomotion is unclear. Some experimental studies claim that the endothelium is necessary for synchronization and vasomotion, whereas others report rhythmic contractions in the absence of an intact endothelium. Moreover, endothelium-derived factors have been shown to abolish vasomotion by desynchronizing the calcium signals in SMCs. By modeling the calcium dynamics of a population of SMCs coupled to a population of endothelial cells, we analyze the effects of an SMC vasoconstrictor stimulation on endothelial cells and the feedback of endothelium-derived factors. Our results show that the endothelium essentially decreases the SMCs calcium level and may move the SMCs from a steady state to an oscillatory domain, and vice versa. In the oscillatory domain, a population of coupled SMCs exhibits synchronous calcium oscillations. Outside the oscillatory domain, the coupled SMCs present only irregular calcium flashings arising from noise modeling stochastic opening of channels. Our findings provide explanations for the published contradictory experimental observations.
Asunto(s)
Arterias/fisiología , Endotelio Vascular/fisiología , Músculo Liso Vascular/fisiología , Arterias/citología , Factores Biológicos/fisiología , Fenómenos Biofísicos , Biofisica , Señalización del Calcio , Comunicación Celular , Endotelio Vascular/citología , Técnicas In Vitro , Matemática , Modelos Cardiovasculares , Contracción Muscular/fisiología , Músculo Liso Vascular/citología , Vasoconstricción/fisiologíaRESUMEN
Many experimental studies have shown that arterial smooth muscle cells respond with cytosolic calcium rises to vasoconstrictor stimulation. A low vasoconstrictor concentration gives rise to asynchronous spikes in the calcium concentration in a few cells (asynchronous flashing). With a greater vasoconstrictor concentration, the number of smooth muscle cells responding in this way increases (recruitment) and calcium oscillations may appear. These oscillations may eventually synchronize and generate arterial contraction and vasomotion. We show that these phenomena of recruitment and synchronization naturally emerge from a model of a population of smooth muscle cells coupled through their gap junctions. The effects of electrical, calcium, and inositol 1,4,5-trisphosphate coupling are studied. A weak calcium coupling is crucial to obtain a synchronization of calcium oscillations and the minimal required calcium permeability is deduced. Moreover, we note that an electrical coupling can generate oscillations, but also has a desynchronizing effect. Inositol 1,4,5-trisphosphate diffusion does not play an important role to achieve synchronization. Our model is validated by published in vitro experiments obtained on rat mesenteric arterial segments.