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Tachykinins intermediate

Substance K

Substance K is a tachykinin neuropeptide that activates NK2 receptors to mediate smooth muscle contraction and inflammatory responses in mammalian tissues.

By Encyclopeptide Editorial | 2 min read
tachykinin NK2-receptor smooth-muscle neuropeptide

Overview

Substance K, also designated as neurokinin A (NKA), is a member of the tachykinin family of bioactive neuropeptides. Characterized by the conserved C-terminal pentapeptide sequence Phe-X-Gly-Leu-Met-NH2, Substance K consists of a decapeptide (10 amino acids) with the sequence His-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met-NH2. It was first isolated from porcine spinal cord in the early 1980s and subsequently identified as a product of the preprotachykinin-A (PPT-A) gene.

Biosynthesis and Distribution

Substance K is co-expressed with substance P and neurokinin B within neurons of the central and peripheral nervous systems. The PPT-A gene undergoes alternative splicing to produce multiple mRNA variants, with the alpha and beta isoforms encoding both substance P and Substance K. Immunohistochemical studies reveal high concentrations in the dorsal root ganglia, enteric nervous system, and respiratory epithelium.

Receptor Pharmacology

Substance K exerts its biological effects preferentially through the NK2 receptor (NK2R), a G protein-coupled receptor coupled to Gq/11 signaling. NK2R activation stimulates phospholipase C activity, generating inositol trisphosphate and diacylglycerol, which mobilize intracellular calcium and activate protein kinase C. The binding affinity of Substance K for NK2R is approximately 10-fold higher than for NK1R, establishing it as the endogenous NK2R agonist.

Biological Functions

Substance K mediates potent smooth muscle contraction in bronchial, gastrointestinal, and urogenital tissues. In the respiratory tract, it causes bronchoconstriction and mucus secretion, contributing to airway hyperresponsiveness in asthmatic conditions. Within the gastrointestinal system, it stimulates peristaltic activity and modulates fluid secretion. Additionally, Substance K participates in neurogenic inflammation by promoting vasodilation and plasma extravasation.

Clinical Significance

Dysregulation of Substance K signaling has been implicated in asthma, inflammatory bowel disease, and bladder overactivity. Selective NK2 receptor antagonists have been developed as potential therapeutic agents for these conditions, with several compounds reaching clinical trials for irritable bowel syndrome and overactive bladder.

References

  1. Maggi, C.A. (2000). The mammalian tachykinin receptors. General Pharmacology, 32(1), 1-48.
  2. Patacchini, R., et al. (2004). Tachykinin receptors and intestinal motility. Peptides, 25(3), 449-464.
  3. Joos, G.F., et al. (2000). Neurokinin antagonists and their potential in airway diseases. Drugs, 59(4), 857-873.

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