Membrane cholesterol depletion with beta-cyclodextrin impairs pressure-induced contraction and calcium signalling in isolated skeletal muscle arterioles.

OBJECTIVE: Given evidence for clustering of signalling molecules and ion channels in cholesterol-rich membrane domains, the involvement of such structures in arteriolar smooth muscle mechanotransduction was examined.
METHOD: To determine the contribution of smooth muscle cholesterol-rich membrane domains to the myogenic response, isolated arterioles were exposed to the cholesterol-depleting agent beta-cyclodextrin (1-10 mM) in the absence and presence of excess exogenous cholesterol.
RESULTS: beta-Cyclodextrin significantly impaired pressure-induced vasoconstriction, while excess cholesterol attenuated this effect. Impaired myogenic constriction was evident in de-endothelialized vessels, indicating an action at the level of smooth muscle. beta-Cyclodextrin treatment uncoupled increases in intracellular Ca(2+) from myogenic constriction and depleted intracellular Ca(2+) stores consistent with a loss of connectivity between plasma membrane and sarcoplasmic reticulum signalling. However, beta-cyclodextrin-treated arterioles showed unaltered constrictor responses to KCl and phenylephrine. Electron microscopy verified that beta-cyclodextrin caused a decrease in caveolae, while confirmation of smooth muscle containing caveolae was obtained by immunostaining for caveolin-1. Viability of beta-cyclodextrin-treated arterioles was confirmed by agonist sensitivity and propidium iodide nuclear staining.
CONCLUSION: The data suggest that smooth muscle cholesterol-rich membrane domains contribute to the myogenic response. Further studies are required to determine whether this relates to specific mechanosensory events or generalized alterations in membrane function.