Affiliation:
1. From the Departments of Pharmacology and Toxicology and Physiology, Medical College of Wisconsin, Milwaukee.
Abstract
Abstract
—A sphingomyelin metabolite, ceramide, serves as a second messenger in a variety of mammalian cells. Little is known regarding the production and actions of this novel intracellular signaling lipid molecule in the vasculature. The present study was designed to test the hypothesis that a ceramide-mediated signaling pathway is present in coronary arterial smooth muscle and that ceramide serves as an inhibitor of the large-conductance Ca
2+
-activated potassium (K
Ca
) channels and mediates vasoconstriction in coronary circulation. We found that C
2
-ceramide produced a concentration-dependent decrease in K
Ca
channel activity in vascular smooth muscle cells from small bovine coronary arteries. The average channel activity of the K
Ca
channels in cell-attached patches decreased from 0.046±0.01 to 0.008±0.001 at a C
2
-ceramide concentration of 10 μmol/L. In inside-out patches, C
2
-ceramide (1 μmol/L) reduced the average channel activity of the K
Ca
channels from 0.06±0.007 to 0.016±0.004. Dithiothreitol, an inhibitor of acidic sphingomyelinase (1 mmol/L), increased the average channel activity of the K
Ca
channels in cell-attached patches from 0.05±0.02 of control to 0.26±0.04, a 5-fold increase that was reversed by addition of 1 μmol/L ceramide. Glutathione, an inhibitor of neutral sphingomyelinase, was without effect. C
2
-ceramide significantly reduced the diameter of isolated perfused small coronary arteries in a concentration-dependent manner. Addition of 1 μmol/L C
2
-ceramide decreased average arterial diameter by 28%. When
14
C-sphingomyelin was incubated with coronary arterial homogenates at pH 7.4 and pH 5.0,
14
C–choline phosphate and ceramide were produced. The conversion rates of
14
C-sphingomyelin into
14
C–choline phosphate and ceramide were 65.1±1.0 fmol/min per milligram protein at pH 7.4 and 114.6±8.3 fmol/min per milligram protein at pH 5.0. We conclude that both acidic and neutral sphingomyelinases are present in the bovine coronary arteries and that ceramide inactivates the K
Ca
channel in arterial smooth muscle cells and hence exerts a tonic vasoconstrictor action in coronary microcirculation.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Cited by
49 articles.
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