In Vivo Endothelial Denudation Disrupts Smooth Muscle Caveolae and Differentially Impairs Agonist-Induced Constriction in Small Arteries

Abstract

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 microm 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 alpha1-adrenoceptor (alpha1-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 alpha2-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-beta-cyclodextrin, there was a similar impairment in constriction to endothelin-1 or alpha2-AR stimulation, but not alpha1-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.