Sheila Flavahan

Rho Kinase Mediates Cold-Induced Constriction of Cutaneous Arteries Role of α2C-Adrenoceptor Translocation

Cold-induced vasoconstriction in cutaneous blood vessels is mediated in part by increased activity of vascular smooth muscle &agr;2-adrenoceptors (VSM &agr;2-ARs). In mouse cutaneous arteries, &agr;2C-ARs are normally silent at 37°C but mediate cold-induced augmentation of &agr;2-AR responsiveness. In transfected HEK293 cells, this functional rescue is mediated by cold-induced translocation of &agr;2C-ARs from the Golgi to the plasma membrane. Experiments were performed to determine the role of Rho/Rho kinase signaling in this process. Inhibition of Rho kinase (fasudil, Y27632 or H-1152) did not affect constriction of isolated mouse tail arteries to the &agr;2-AR agonist UK 14 304 at 37°C but dramatically reduced the augmented responses to the agonist at 28°C. After Rho kinase inhibition, cooling no longer increased constriction evoked by &agr;2-AR stimulation. Cooling (to 28°C) activated Rho in VSM cells and increased the calcium sensitivity of constriction in &agr; toxin-permeabilized arteries. Stimulation of &agr;2-ARs in VSM cells had no effect on Rho activity or calcium sensitivity at 37°C or 28°C. In HEK293 cells transfected with &agr;2C-ARs, cooling (to 28°C) stimulated the translocation of &agr;2C-ARs to the plasma membrane and this effect was prevented by inhibition of Rho kinase, using fasudil or RNA interference. Consistent with inhibition of the spatial rescue of &agr;2C-ARs, fasudil inhibited &agr;2-AR–mediated mobilization of calcium in tail arteries at 28°C but not 37°C. Therefore, cold-induced activation of Rho/Rho kinase can mediate cold-induced constriction in cutaneous arteries by enabling translocation of &agr;2C-ARs to the plasma membrane and by increasing the calcium sensitivity of the contractile process.

The vasculopathy of Raynaud's phenomenon and scleroderma.

The scleroderma (SSc) disease process involves dramatic dysfunction in acute and chronic vascular regulatory mechanisms; it presents initially with heightened vasoconstrictor or vasospastic activity and progresses to structural derangement or vasculopathy of the microcirculation. This article discusses the regulatory mechanisms that contribute to this dysfunction and the vascular changes in the context of the other aspects of the SSc disease process in a novel attempt to integrate the individual pathologies of the disease process.

In vivo endothelial denudation disrupts smooth muscle caveolae and differentially impairs agonist-induced constriction in small arteries

Experiments were performed to determine the effects of endothelial denudation in vivo on vasoconstrictor responses of mouse tail artery segments in vitro. A sterile wire (70 μm diameter) was inserted into tail arteries of anesthetized mice to mechanically denude the endothelium, and the animals were allowed to recover for 48 hours. The function of pressurized tail artery segments was then studied in vitro. Intimal injury markedly reduced endothelium-dependent relaxation to acetylcholine. Constriction evoked by the selective α1-adrenoceptor (α1-AR) agonist, phenylephrine, was not affected by in vivo endothelial denudation, indicating that the contractile function of vascular smooth muscle cells (VSMCs) was not impaired. However, constriction to the selective α2-AR agonist UK14304 or to endothelin-1 was significantly inhibited. Confocal microscopy of intact tail arteries localized caveolin-1 to punctuate structures, arranged in rows on or close to the surface of VSMCs. After in vivo endothelial denudation, this pattern was disrupted and caveolin-1 was localized to intracellular sites. When VSMC caveolae were disrupted in control arteries using the cholesterol acceptor methyl-β-cyclodextrin, there was a similar impairment in constriction to endothelin-1 or α2-AR stimulation, but not α1-AR activation. These results suggest that intimal injury to small cutaneous arteries disrupts VSMC surface caveolae and selectively impairs constriction to stimuli that are dependent on these structures for signaling.