Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC352
Caveolar disruption with methyl-β-cyclodextrin (MCD) causes endothelium-dependent contraction of rat femoral arteries
A. Al-Brakati1, T. Kamishima1, C. Dart2, J. Quayle1
1. Institute of Translational Medicine, Liverpool University, Liverpool, United Kingdom. 2. Institute of Integrative Biology, Liverpool University, Liverpool, United Kingdom.
Caveolae are flask shaped invaginations in the cell membrane which act as signalling hubs in endothelial and smooth muscle cells (1,2). Disruption of caveolae by the membrane cholesterol depleting agent MCD has various functional effects on arteries, including impairment of endothelium-dependent relaxation (1), and augmentation of smooth muscle contraction independently of the endothelium (2). The aim of this study was to explore the effects of MCD on contraction of rat femoral arteries. Methods: Isometric force was measured in rat femoral artery in a resistance artery myograph. Arteries were stimulated to contract with a solution containing 20 mM K+ and 100 nM BayK 8644 (20K/BayK). Data are expressed as mean ± SEM, compared by Student’s t-test. Results: Incubation of arteries with MCD (5 mM, 60 min) increased force in response to 20K/BayK from 11.84 ± 1.30 mN to 18.25 ± 2 mN (n = 12, P < 0.01). In contrast, contraction induced by 80 mM K+ was not altered by MCD (33.40 ± 1.43 mN to 33.16 ± 2.02 mN, n = 12, P = n.s.). Filipin, which also disrupts caveoli, also significantly increased force to 20K/BayK (5.36 ± 1.66 mN to 9.36± 2.21 mN, n =14, P ≤ 0.01). Cholestrol saturated MCD (Ch-MCD, 5 mM, 50 min) had no effect on its own on 20K/BayK induced force (3.15 ± 0.45 mN to 2.98 ± 0.59 mN, n = 4, P= n.s.), but reversed the effects of MCD (3.50 ± 0.62 mN in 20K/BayK, 4.93 ± 1.35 mN after MCD, 2.74 ± 0.59 mN after Ch-MCD, n=16). Functional effects of caveolar disruption have been reported to be both endothelium-dependent and endothelium-independent (1,2). Mechanical removal of endothelial cells from femoral artery reduced the ability of MCD to enhance contractions to 20K/BayK (6.62 ± 0.92 mN to 7.52 ± 1.03 mN after MCD, n = 22, P = n.s.). This result suggests MCD acts via altering basal release of an endothelial-derived vasodilator or vasoconstrictor. When endothelial release of nitric oxide (NO) was blocked by pre-incubation of arteries with L-NAME (250 μM), contraction of arteries to 20K/BayK was enhanced (6.82 ± 1.61 mN to 14.90 ± 2.67 mN, n = 6, P<0.01). Subsequent treatment of these arteries with MCD caused contraction, and L-NAME no longer had a significant effect after MCD treatment (17.74 ± 3.46 mN after MCD, 16.10 ± 3.19 mN in L-NAME and MCD, n = 6, P = n.s). Conclusion: We provide evidence that the caveolar disrupting agents MCD and filipin increase contraction of rat femoral arteries. Our results are consistent with caveolar disruption resulting in decreased basal release of endothelium-dependent vasodilators, probably NO.
Where applicable, experiments conform with Society ethical requirements