biology

Κ-opioid receptor

Κ-opioid receptor is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Κ-opioid receptor rather than just read about it. In short: The κ-opioid receptor or kappa opioid receptor, abbreviated KOR or KOP for its ligand ketazocine, is a G protein-coupled receptor that is encoded by the OPRK1 gene in humans. The KOR is coupled to the G protein Gi/G0 and is among related receptors that bind opioid-like compounds in the brain and are responsible for mediating the effects of these compounds.

Key takeaways

Κ-opioid receptor belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Κ-opioid receptor to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Κ-opioid receptor from memory before moving on to harder problems.

Reference excerpt

The κ-opioid receptor or kappa opioid receptor, abbreviated KOR or KOP for its ligand ketazocine, is a G protein-coupled receptor that is encoded by the OPRK1 gene in humans. The KOR is coupled to the G protein Gi/G0 and is among related receptors that bind opioid-like compounds in the brain and are responsible for mediating the effects of these compounds. These include altering nociception, mood, reward system, and motor control. KOR is one of the two opioid receptors that bind dynorphin opioid peptides as the primary endogenous ligands, the other being newly deorphanized GPR139 receptor. In addition, oxytocin was found to be a positive allosteric modulator of KOR, and a variety of natural alkaloids, terpenoids, and synthetic ligands bind to the receptor. Dysregulation of this receptor system has been implicated in multiple psychiatric disorders including: depressive and anxiety disorders, disorders of diminished motivation, schizophrenia, borderline personality disorder, bipolar disorder, and substance use disorder. Ligands binding to the receptor have been approved the treatment of pruritus and pain management. Aside from those indications they are investigated for various psychiatric disorders, irritable bowel syndrome, and acute stroke.

Tissue distribution

Central nervous system

Brain KORs are widely distributed throughout the brain. The claustrum represents the brain region with the highest density of KOR expression. Other CNS regions expressing moderate to high KOR densities include the prefrontal cortex, periaqueductal gray, dorsal raphe nuclei (dorsal), ventral tegmental area, substantia nigra, dorsal striatum (putamen, caudate), ventral striatum (nucleus accumbens, olfactory tubercle), amygdala, bed nucleus of the stria terminalis, hippocampus (pyramidal and molecular layers, granular cell layer of the dentate gyrus), hypothalamus, thalamus (centromedian, paraventricular, and centrolateral nuclei), locus coeruleus, spinal trigeminal nucleus, parabrachial nucleus, and solitary nucleus. Positron emission tomography (PET) imaging studies with the KOR-selective radioligand [11C]GR-103545 in non-human primates showed high binding potential (BPND > 1.3) in the pituitary gland, followed by insula, claustrum, and orbitofrontal cortex, with moderate binding (BPND 0.9–1.3) in nucleus accumbens, amygdala, and hippocampus. [3H]bremazocine binding showed elevated densities along the ventral edge of the nucleus accumbens and ventral putamen regions. There is evidence that distribution and/or function of this receptor may differ between sexes.

Spinal cord In spinal cord, KOR is expressed in the substantia gelatinosa and superficial laminae of the dorsal horn, where they modulate thermal nociception and chemical viscelar pain. They are concentrated in the upper laminae of the dorsal horn (laminae I–III) and within the posterolateral tract. The highest density was localized within the inner segment of lamina II, forming a dense band immediately dorsal to lamina III. 53% of KOR binding sites in the superficial dorsal horn (laminae I–II) are localized presynaptically on primary afferent terminals, with the remainder distributed postsynaptically.

Peripheral nervous system

Dorsal root ganglia KOR is present in dorsal root ganglia (DRG) in moderate expression levels in human tissue. KOR is expressed in peptidergic primary afferents genes encoding calcitonin gene-related peptide (CGRP) and substance P, as well as in populations of low-threshold mechanoreceptors that innervate hair follicles. In human DRG neurons, approximately 25% cells express OPRK1 mRNA.

Immune cells In immune cells, KOR is distributed in specific leukocyte populations. Approximately 50% of resident peritoneal macrophages express KOR, while expression decreases during lymphocyte maturation, with less than 25% of splenic T-helper or T-cytotoxic lymphocytes and only 16% of splenic B lymphocytes displaying receptor expression.

Gastrointestinal tract In the gastrointestinal tract, KOR is expressed on myenteric and submucosal plexus neurons, where they modulate intestinal motility and secretion. Both KOR and MOR mRNAs are expressed in all investigated gastrointestinal regions in one study, with the stomach and proximal colon displaying the highest expression levels, and the duodenum exhibiting the lowest. KOR in the proximal colon represented 40% of the amount found in the brain. A higher number of neurons expressing KOR-like immunoreactivity are visualized in the myenteric plexus with a smaller number in the submucosal plexus, unlike the distribution pattern of MORs.

Cardiovascular system KORs are expressed in human cardiac tissue, including cardiomyocytes, where they exert negative inotropic and lusitropic effects through pertussis toxin-sensitive Gi/o protein signaling.

Renal system Healthy human kidney expresses KOR, yet detailed cellular localization within specific nephron segments aren't investigated.

Subtypes Based on receptor binding studies, three variants of the KOR: κ1, κ2, and κ3 have been characterized via radioligand binding and regional CNS mapping. However, only one encoding cDNA has been cloned, hence these subtypes likely arise from interactions of the KOR protein with other membrane-associated proteins rather than gene duplication. Historically the understanding that KORs are encoded by a single gene reopened the question of how one receptor system could be involved in such a multiplicity of interactions and disparate profiles.

Function

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Illustrations

Worked examples

Example 1 — a first encounter with Κ-opioid receptor

Start with the simplest possible case. Write down what Κ-opioid receptor claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Κ-opioid receptor before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Κ-opioid receptor ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Κ-opioid receptor

In research: Κ-opioid receptor appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Κ-opioid receptor in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Κ-opioid receptor is common in secondary-school and first-year university syllabi. It links to neighbouring topics Genes on human chromosome 8, Kappa-opioid receptor agonists, Opioid receptors, so understanding it makes those chapters shorter.
In everyday life: Look for Κ-opioid receptor outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Κ-opioid receptor in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Κ-opioid receptor means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Κ-opioid receptor out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Κ-opioid receptor in simple terms?

Why does Κ-opioid receptor matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Κ-opioid receptor?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Κ-opioid receptor.