Ecto-5'-nucleotidase, CD73, is an endothelium-derived hyperpolarizing factor synthase

Area of Science:

• Cardiovascular Physiology
• Endothelial Cell Biology
• Enzymology

Background:

• Adenosine mediates coronary vasodilation through potassium channel activation, independent of endothelial cells.
• Ecto-5'-nucleotidase (CD73) converts extracellular adenosine 5'-monophosphate to adenosine.
• Endothelium-derived hyperpolarizing factors (EDHF) play a crucial role in regulating vascular tone.

Purpose of the Study:

• To investigate if coronary vasodilation to adenine nucleotides is mediated by endothelial CD73-dependent adenosine production.
• To determine if this adenosine acts as an EDHF.

Main Methods:

• Videomicroscopy of human coronary arteries.
• Inhibition studies using nitric oxide synthase, prostacyclin, adenosine receptor antagonists, adenosine deaminase, and CD73 blockers.
• Liquid chromatography-electrospray ionization-mass spectrometry for adenosine detection.
• Localization of CD73 expression.
• Studies in CD73-deficient mouse coronary arteries.

Main Results:

• Adenine nucleotides, but not inosine, caused potent vasodilation and hyperpolarization of human coronary arteries, independent of nitric oxide and prostacyclin.
• Endothelial denudation, CD73 blockade, or adenosine deaminase significantly reduced these vasodilations.
• Adenosine accumulation was detected in perfusates with adenosine diphosphate.
• CD73 was found on endothelial cells, and its deficiency impaired vasodilation to adenine nucleotides in mouse arteries.
• Adenosine produced similar dose-dependent vasodilation and hyperpolarization as adenosine diphosphate.

Conclusions:

• Coronary vasodilation induced by adenine nucleotides involves endothelial CD73-dependent extracellular adenosine production.
• This adenosine functions as an EDHF, relaxing and hyperpolarizing vascular smooth muscle cells via adenosine receptors.
• CD73 represents a novel EDHF synthase in both human and mouse coronary arteries.