Cholesterol-induced changes in rabbit arterial smooth muscle sensitivity to adrenergic stimulation

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Abstract
We evaluated the effects of exposure to high cholesterol levels for 3 h on arterial smooth muscle responses to adrenergic stimulation. Femoral arteries from Dutch belted rabbits were perfused in vitro with a constant-flow variable-pressure perfusion apparentus. After equilibration the vessels were perfused for 180 min more with media supplemented with cholesterol-phospholipid (C/PL) liposomes of molar ratios of 2:1 or 0.5:1. Although resting vascular resistance was unchanged, norepinephrine (NE) concentration-response analyses revealed a fivefold increase in NE sensitivity (P less than 0.001) in the arteries perfused with the cholesterol-enriched liposomes (2:1) compared with control arteries perfused with the 0.5:1 liposome medium. The arteries perfused with the cholesterol-enriched liposomes demonstrated a 60% increase in cholesterol content and a marked (90%) reduction in Na+-K+-ATPase activity. The increased sensitivity of the cholesterol-enriched arteries was not mediated by acute reductions in Na-pump activity, altered endothelial function, adrenergic nerve function, or prostaglandin production. Cholesterol-induced sensitization to NE did demonstrate an absolute dependence on extra-cellular calcium. These findings suggest that an increase in the free cholesterol content of the arterial smooth muscle cell plasma membrane alters membrane permeability to extracellular calcium during adrenergic stimulation.