Functional alpha-1B adrenergic receptors on human epicardial coronary artery endothelial cells

Area of Science:

• Cardiovascular Biology
• Molecular Pharmacology
• Endothelial Cell Biology

Background:

• Alpha-1-adrenergic receptors (α1-ARs) bind catecholamines like norepinephrine (NE) and epinephrine (EPI), influencing coronary blood flow.
• While α1-ARs are known in coronary smooth muscle cells (SMCs), their presence and function in human coronary endothelial cells (ECs) remain uncharacterized.
• The α1D subtype predominates in human epicardial coronary arteries, but EC expression is unknown.

Purpose of the Study:

• To investigate the expression and function of α1-ARs in human epicardial coronary artery endothelial cells (ECs).
• To determine which α1-AR subtypes are present and active in these ECs.
• To understand the signaling pathways activated by α1-ARs in ECs.

Main Methods:

• Quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) for mRNA analysis.
• Radioligand binding assays to quantify receptor density.
• Immunoblotting to detect protein expression.
• (3H)-thymidine incorporation assays to assess DNA synthesis.
• Stimulation with NE and EPI to evaluate functional responses.

Main Results:

• Human epicardial coronary ECs express α1-ARs, with the α1B subtype mRNA being predominant (90-95%).
• ECs exhibited twice the α1-AR binding density compared to coronary SMCs.
• NE and EPI, via the α1B subtype, activated extracellular signal-regulated kinase (ERK) and phosphorylated endothelial nitric oxide synthase (eNOS) in ECs.
• α1-AR activation stimulated DNA synthesis in ECs.

Conclusions:

• This study provides the first evidence of functional α1-ARs, predominantly the α1B subtype, on human coronary ECs.
• α1-AR activation in ECs triggers signaling pathways (ERK, eNOS phosphorylation) and promotes cell proliferation.
• These findings suggest a novel mechanism for the cardiovascular effects of nonselective α1-AR antagonists.