A(1) adenosine receptors in human neutrophils: direct binding and electron microscope visualization

Area of Science:

• Immunology
• Cell Biology
• Pharmacology

Background:

• Adenosine and its analogues modulate neutrophil functions by binding to specific surface receptors.
• A(1) adenosine receptors are known to influence neutrophil chemotaxis, but their binding characteristics and visualization in human neutrophils remain uncharacterized.

Purpose of the Study:

• To investigate the specific agonist binding and visualize A(1) adenosine receptors in human neutrophils.
• To characterize the binding affinity and density of A(1) receptors.
• To track the internalization and intracellular trafficking of A(1) receptors.

Main Methods:

• Radioligand binding studies using the agonist [(3)H] CHA.
• Visualization of A(1) binding sites using a CHA-biotin XX probe conjugated with colloidal gold-streptavidin.
• Ultrastructural analysis of human neutrophils.
• Controlled temperature experiments to study ligand-receptor complex internalization.

Main Results:

• [(3)H] CHA demonstrated selective and specific binding to A(1) adenosine receptors with a dissociation constant (Kd) of 1.4 +/- 0.08 nM and a maximum binding site density of 7.1 +/- 0.37 fmol/mg of proteins.
• The CHA-biotin XX probe successfully visualized A(1) receptors as electron-dense gold particles on and within neutrophils.
• Ligand-receptor complex internalization occurred via a receptor-mediated pathway with rapid intracellular trafficking (<5 min).

Conclusions:

• The CHA-biotin XX-streptavidin-gold complex serves as an effective marker for specifically labeling A(1) adenosine binding sites in human neutrophils.
• This approach enables the visualization and tracking of A(1) receptor dynamics, including their rapid internalization.
• The findings provide valuable insights into the function and trafficking of A(1) adenosine receptors in neutrophils.