Abstract
Background and Purpose. Caveolae act as signalling hubs in endothelial and smooth muscle cells. Caveolar disruption by the membrane cholesterol depleting agent methyl-beta-cyclodextrin (M-beta-CD) has various functional effects on arteries including (i) impairment of endothelium-dependent relaxation, and (ii) alteration of smooth muscle cell (SMC) contraction independently of the endothelium. The aim of this study was to explore the effects of M-beta-CD on rat femoral arteries.
Methods. Isometric force was measured in rat femoral arteries stimulated to contract with a solution containing 20 mM K+ and 200 nM Bay K 8644 (20 K/Bay K) or with one containing 80 mM K+ (80 K).
Results. Incubation of arteries with M-beta-CD (5 mM, 60 min) increased force in response to 20 K/Bay K but not that induced by 80 K. Application of cholesterol saturated M-beta-CD (Ch-MCD, 5 mM, 50 min) reversed the effects of M-beta-CD. After mechanical removal of endothelial cells M-beta-CD caused only a small enhancement of contractions to 20 K/Bay K. This result suggests M-beta-CD acts via altering release of an endothelial-derived vasodilator or vasoconstrictor. When nitric oxide synthase was blocked by pre-incubation of arteries with L-NAME (250 mu M) the contraction of arteries to 20 K/Bay K was enhanced, and this effect was abolished by pre-treatment with M-beta-CD. This suggests M-beta-CD is inhibiting endothelial NO release. Inhibition of large conductance voltage- and Ca2+-activated (BKCa) channels with 2 mM TEA(+) or 100 nM Iberiotoxin (IbTX) enhanced 20 K/Bay K contractions. L-NAME attenuated the contractile effect of IbTX, as did endothelial removal.
Conclusions. Our results suggest caveolar disruption results in decreased release of endothelial-derived nitric oxide in rat femoral artery, resulting in a reduced contribution of BKCa channels to the smooth muscle cell membrane potential, causing depolarisation and contraction.