Competitive antagonists discriminate between NK2 tachykinin receptor subtypes

Area of Science:

• Pharmacology
• Neuroscience
• Physiology

Background:

• Tachykinins are peptides that bind to specific receptors, influencing various physiological processes.
• NK2 receptors are implicated as key mediators of tachykinin-induced contractions in smooth muscles like the rabbit pulmonary artery (RPA) and hamster trachea (HT).

Purpose of the Study:

• To compare the contractile responses induced by tachykinins and selective agonists in RPA and HT.
• To evaluate the affinity of novel NK2-selective antagonists in these tissues.
• To investigate potential heterogeneity of NK2 receptors.

Main Methods:

• Experiments were conducted on endothelium-denuded rabbit pulmonary artery (RPA) and hamster trachea (HT).
• Tachykinins and selective NK2 receptor agonists were used to induce contractions.
• Three novel peptide antagonists were tested for their ability to inhibit NKA-induced contractions.
• Schild plot analysis was used to determine antagonist affinity (pA2 values).

Main Results:

• NK2 receptors were confirmed as the primary mediators of tachykinin responses in both RPA and HT.
• Three NK2 antagonists demonstrated competitive antagonism, with varying potencies between RPA and HT.
• Peptides I and II were approximately 100 times more potent in RPA than HT, while Peptide III was 100 times more potent in HT than RPA.
• Antagonists showed no cross-reactivity with NK1 or NK3 receptors or other agonists.

Conclusions:

• The findings provide pharmacological evidence for heterogeneity of NK2 receptors in RPA and HT.
• While natural tachykinins and selective agonists do not distinguish between these NK2 receptors, novel antagonists reveal significant differences in their binding affinities.
• This suggests the existence of distinct NK2 receptor subtypes or conformations in different tissues.