Roger Sauser

Force Transmission in Migrating Cells

Analysis of the relationship between actin network velocity and traction forces at the substrate shows that force transmission mechanisms vary with distinct regions of the cell.

Intercellular calcium waves are associated with the propagation of vasomotion along arterial strips

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.

Does the Endothelium Abolish or Promote Arterial Vasomotion in Rat Mesenteric Arteries? Explanations for the Seemingly Contradictory Effects

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.

Recruitment of Smooth Muscle Cells and Intercellular Calcium Waves during Arterial Vasomotion

Vasomotion is a natural property of small arteries and arterioles. Vasomotion consists in cyclic diameter variations, which are induced by synchronous contractions of the smooth muscle cells (SMCs) present in the arterial wall. These contractions have been shown to be due to an increase in the SMCs cytosolic calcium concentration. The present study was performed on rat mesenteric arterial strips. The first part investigated the response of SMCs under different concentrations of phenylephrine (PE), a vasoconstrictor, with an emphasis on the synchronization of SMCs in endothelium denuded strips. We observed that the recruitment of the SMCs increased with the PE concentration and vasomotion appeared only when a sufficient number of SMCs were recruited and synchronized.