Substance P receptor on parotid cell membranes

Area of Science:

• Neuroendocrinology
• Cellular Biology
• Pharmacology

Background:

• Substance P (SP) is a neuropeptide involved in various physiological processes, including salivary secretion.
• Understanding the molecular mechanisms of SP action is crucial for elucidating its role in glandular function.

Purpose of the Study:

• To characterize the binding properties of substance P on rat parotid cells.
• To identify the minimal structural requirements for substance P binding and biological activity.
• To investigate the nature of the substance P binding site.

Main Methods:

• Radioligand binding assays using 125I-labeled Bolton-Hunter reagent conjugated to substance P (125I-BH-SP).
• Competition binding studies with substance P fragments and analogs.
• Enzymatic treatment of cells (papain, RNase A, DNase I) to assess the nature of the binding site.

Main Results:

• 125I-BH-SP binds to a single class of high-affinity (Kd = 4 nM) sites on rat parotid cells.
• Binding affinity of SP fragments correlates with their saliva-stimulating potency.
• The COOH-terminal hexa(6-11)peptide is the smallest fragment with significant binding and activity.
• Binding is specific for SP and not affected by unrelated neurotransmitters or hormones.
• Binding activity is abolished by papain, suggesting a proteinaceous receptor.

Conclusions:

• Rat parotid cells possess high-affinity binding sites for substance P.
• These binding sites are likely substance P receptors located on parotid membranes.
• The receptor exhibits characteristics of a protein, at least in part.