GO:0044557 relaxation of smooth muscle: Mechanisms, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0044557 (relaxation of smooth muscle) describes the biological process by which the extent of smooth muscle contraction is reduced, a fundamental homeostatic mechanism in hollow organs and blood vessels.
• Nitric oxide (NO) released from endothelium or nitrergic nerves is a primary mediator of smooth muscle relaxation, acting via hyperpolarization and cyclic GMP signaling.
• Prostaglandin E2 and pulmonary surfactant act as local relaxants in airway smooth muscle, with effects conserved between human and guinea pig tissues.
• Drotaverine and multitarget inhibitors represent pharmacological tools that directly relax tracheal and other smooth muscles, highlighting therapeutic relevance.
• Adenosine and other purinergic agonists relax vascular smooth muscle through receptor-mediated pathways, contributing to blood flow regulation.
• Relaxation of smooth muscle is critical in airway diseases (asthma), vascular disorders (hypertension), and urogenital conditions (urethral obstruction), making it a key research target.
Description
Relaxation of smooth muscle (GO:0044557) is a fundamental biological process defined as the reduction in the extent of smooth muscle contraction. Smooth muscle differs from striated muscle in its much higher actin/myosin ratio, absence of conspicuous sarcomeres, and ability to contract to a much smaller fraction of its resting length. This process is essential for the normal function of hollow organs, including blood vessels, airways, gastrointestinal tract, and urogenital system. Dysregulation of smooth muscle relaxation contributes to diseases such as asthma, hypertension, and erectile dysfunction. Understanding the molecular and cellular mechanisms of relaxation is therefore critical for developing targeted therapies. This article synthesizes authoritative QuickGO data and verified PubMed literature to provide a research-grade overview of GO:0044557, covering its definition, mechanisms, key genes, disease associations, and experimental models.
relaxation of smooth muscle At A Glance
| GO ID | GO:0044557 |
|---|---|
| GO term | relaxation of smooth muscle |
| Ontology | biological_process |
| Synonym | smooth muscle relaxation |
| Definition | A process in which the extent of smooth muscle contraction is reduced. Smooth muscle differs from striated muscle in the much higher actin/myosin ratio, the absence of conspicuous sarcomeres and the ability to contract to a much smaller fraction of its resting length. |
| Major function | Reduction of smooth muscle tone in hollow organs and blood vessels |
| Key mediators | Nitric oxide, prostaglandin E2, adenosine, pharmacological agents (e.g., drotaverine) |
| Associated diseases | Asthma, hypertension, urethral obstruction, ocular hypertension |
| Research methods | Organ bath myography, calcium imaging, patch clamp, CRISPR knockout models |
What Is GO:0044557?
GO:0044557, relaxation of smooth muscle, is the biological process in which the extent of smooth muscle contraction is reduced. Smooth muscle is characterized by a high actin-to-myosin ratio, the absence of conspicuous sarcomeres, and the ability to contract to a much smaller fraction of its resting length compared to striated muscle. This process is synonymous with smooth muscle relaxation and is essential for regulating organ tone and diameter in response to physiological signals.
Why Is relaxation of smooth muscle Important in Cell Biology?
Relaxation of smooth muscle is a central physiological process that controls the diameter and tone of hollow organs and blood vessels. It is essential for maintaining normal blood pressure, airway patency, gastrointestinal motility, and urogenital function. Dysregulation of this process underlies major human diseases, including asthma, hypertension, and erectile dysfunction. Pharmacological modulation of smooth muscle relaxation is a cornerstone of therapy for these conditions, with agents such as drotaverine and multitarget inhibitors showing efficacy in preclinical models. Thus, understanding the molecular mechanisms of GO:0044557 is critical for both basic physiology and translational medicine.
• Controls vascular tone and blood pressure; NO-mediated relaxation is a key regulator of arterial diameter.
• Regulates airway diameter; impaired relaxation contributes to asthma and bronchoconstriction.
• Modulates urethral and urogenital smooth muscle, affecting micturition and erectile function.
• Influences ocular trabecular meshwork and ciliary muscle, relevant to intraocular pressure and glaucoma.
• Adenosine-mediated relaxation regulates coronary and systemic blood flow.
• Pharmacological targeting of relaxation is used in treating asthma, hypertension, and gastrointestinal spasms.
• Maturation and developmental changes affect airway smooth muscle relaxation mechanisms.
• Prostaglandin E2 and pulmonary surfactant act as local relaxants in the lung.
• Nitric oxide donors are used experimentally to study relaxation in various smooth muscle types.
• Drotaverine is a clinically used smooth muscle relaxant, validating the therapeutic potential of this process.
What Happens During relaxation of smooth muscle?
Initiation by Nitric Oxide and Endothelial Factors
In simple terms: Nitric oxide is a gas that tells smooth muscle to relax.
Nitric oxide (NO) derived from the endothelium diffuses into smooth muscle cells and causes hyperpolarization and relaxation of arterial smooth muscle. This mechanism is a primary pathway for vasodilation. In urethral smooth muscle, NO donors and nitric oxide itself induce relaxation through differential mechanisms, highlighting tissue-specific signaling. Similarly, release of nitric oxide relaxes trabecular meshwork and ciliary muscle, affecting aqueous humor outflow.
Role of Prostaglandins and Surfactant
In simple terms: Local chemicals like prostaglandin E2 and surfactant help airways relax.
Pulmonary surfactant and prostaglandin E2 (PGE2) promote relaxation of airway smooth muscle in both human and male guinea pig tissues. These agents act locally to counteract bronchoconstriction, and their effects are conserved across species, making them relevant for asthma research.
Pharmacological Relaxation by Drotaverine and Multitarget Inhibitors
In simple terms: Certain drugs can directly relax smooth muscle.
Drotaverine, a clinically used antispasmodic, exerts a relaxant effect on airway smooth muscle, as assessed in experimental models. Multitarget inhibitors designed as tracheal smooth muscle relaxants show potential for treating respiratory conditions. These pharmacological tools confirm that relaxation can be induced independently of endogenous signaling.
Adenosine and Purinergic Signaling
In simple terms: Adenosine is a molecule that helps blood vessels relax.
Adenosine relaxes isolated vascular smooth muscle, contributing to the regulation of vascular tone. This purinergic pathway operates alongside NO-mediated relaxation and provides an additional layer of control over blood flow.
Maturation and Developmental Aspects
In simple terms: The ability of smooth muscle to relax changes as the body matures.
Mechanisms of airway smooth muscle relaxation during maturation differ between young and adult animals, with age-dependent changes in signaling pathways. This has implications for pediatric respiratory diseases and for understanding how relaxation capacity develops.
Key Genes Involved in GO:0044557 relaxation of smooth muscle
The following genes and proteins are central to the regulation and execution of relaxation of smooth muscle (GO:0044557), based on verified literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| NOS3 | Endothelial nitric oxide synthase; produces NO that diffuses to smooth muscle | Target for vascular relaxation studies; KO models show impaired vasodilation |
| NOS1 | Neuronal nitric oxide synthase; produces NO in nitrergic nerves | Involved in urethral and gastrointestinal relaxation |
| PTGS2 | Cyclooxygenase-2; synthesizes prostaglandin E2 | PGE2-mediated airway relaxation; target for asthma research |
| ADORA2A | Adenosine A2A receptor; mediates adenosine-induced relaxation | Vascular relaxation studies; KO models alter blood flow |
| ADORA2B | Adenosine A2B receptor; contributes to adenosine signaling | Potential role in vascular and airway relaxation |
| GUCA1A | Guanylate cyclase activator; regulates cGMP production | Downstream of NO signaling in smooth muscle relaxation |
| PRKG1 | cGMP-dependent protein kinase; mediates NO-induced relaxation | Key effector of NO-cGMP pathway; KO models show impaired relaxation |
| MYLK | Myosin light chain kinase; phosphorylates myosin to promote contraction | Inhibition leads to relaxation; target for pharmacological studies |
| PPP1R12A | Myosin phosphatase regulatory subunit; dephosphorylates myosin | Promotes relaxation by opposing MYLK |
| CALD1 | Caldesmon; actin-binding protein that inhibits actomyosin ATPase | Regulates relaxation via actin cytoskeleton |
| ACTA2 | Alpha-actin; major contractile protein in smooth muscle | High actin/myosin ratio is a hallmark of smooth muscle |
| MYH11 | Smooth muscle myosin heavy chain; motor protein | Contraction and relaxation depend on myosin cycling |
| KCNMA1 | Large-conductance calcium-activated potassium channel; promotes hyperpolarization | Hyperpolarization leads to relaxation; target for vasodilators |
| ABCC9 | SUR2 subunit of KATP channels; modulates membrane potential | KATP channel opening causes relaxation; involved in vascular tone |
| PLN | Phospholamban; regulates SERCA calcium pump | Calcium reuptake into SR promotes relaxation |
| ATP2A2 | SERCA2 calcium pump; lowers cytosolic calcium | Essential for relaxation by reducing intracellular Ca2+ |
| RYR2 | Ryanodine receptor; releases calcium from SR | Calcium sparks modulate relaxation in smooth muscle |
| GUCY1A1 | Soluble guanylate cyclase subunit; produces cGMP in response to NO | Central to NO-mediated relaxation |
How Is relaxation of smooth muscle Regulated?
Relaxation of smooth muscle is tightly regulated by multiple signaling pathways. Nitric oxide produced by endothelial or neuronal nitric oxide synthases diffuses into smooth muscle cells and activates soluble guanylate cyclase, leading to cGMP production and activation of protein kinase G, which reduces intracellular calcium and promotes myosin light chain phosphatase activity. Prostaglandin E2 and pulmonary surfactant act through G-protein coupled receptors to increase cAMP and relax airway smooth muscle. Adenosine signals via A2A and A2B receptors to relax vascular smooth muscle. Additionally, maturation affects the expression and function of these pathways, altering relaxation capacity during development. Pharmacological agents such as drotaverine and multitarget inhibitors can bypass endogenous signaling to directly induce relaxation.
relaxation of smooth muscle and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| NOS3 | Hypertension; impaired NO-mediated vasodilation | Endothelial-specific KO mouse; organ bath myography |
| PTGS2 | Asthma; reduced PGE2-mediated airway relaxation | Airway smooth muscle-specific KO; guinea pig tracheal rings |
| ADORA2A | Vascular disorders; altered adenosine relaxation | Global KO mouse; isolated aortic rings |
| NOS1 | Urethral obstruction; impaired nitrergic relaxation | Neuronal NOS KO mouse; urethral smooth muscle strips |
| MYLK | Asthma; increased contractility due to MYLK overactivity | Smooth muscle-specific KO; tracheal rings |
Asthma and Airway Hyperresponsiveness
Impaired relaxation of airway smooth muscle contributes to bronchoconstriction in asthma. Prostaglandin E2 and pulmonary surfactant promote relaxation in human and guinea pig airways, suggesting therapeutic potential. Drotaverine and multitarget inhibitors have been assessed for their relaxant effects on tracheal smooth muscle, highlighting their relevance for asthma treatment. Maturational changes in relaxation mechanisms may affect pediatric asthma severity.
Hypertension and Vascular Disorders
Nitric oxide-mediated relaxation of arterial smooth muscle is critical for blood pressure regulation. Endothelial NO causes hyperpolarization and relaxation, and its dysfunction leads to hypertension. Adenosine also relaxes vascular smooth muscle, providing an additional regulatory pathway. Targeting these pathways is a major therapeutic strategy for vascular diseases.
Urogenital and Ocular Disorders
Relaxation of urethral smooth muscle is essential for normal micturition; impaired relaxation can cause urinary retention. Nitric oxide donors relax urethral smooth muscle through differential mechanisms. In the eye, relaxation of trabecular meshwork and ciliary muscle by nitric oxide affects aqueous humor outflow and intraocular pressure, relevant to glaucoma.
From relaxation of smooth muscle-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of NOS3 impair arterial relaxation? | NOS3 knockout mouse; aortic ring myography |
| Does PTGS2 deletion affect airway relaxation? | PTGS2 knockout mouse; tracheal smooth muscle organ bath |
| Can point mutation in PRKG1 alter NO sensitivity? | PRKG1 point-mutation knock-in mouse; vascular reactivity |
| Does overexpression of ADORA2A enhance adenosine relaxation? | Transgenic overexpression mouse; coronary flow measurement |
| Does tagged MYLK knock-in reveal localization during relaxation? | MYLK-GFP knock-in mouse; live-cell imaging |
| Does smooth muscle-specific knockout of ATP2A2 delay relaxation? | Conditional ATP2A2 KO mouse; calcium imaging |
How to Study the relaxation of smooth muscle Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Organ bath myography | Isometric force of smooth muscle strips | Quantifying relaxation responses to drugs or NO donors |
| Calcium imaging | Intracellular calcium concentration | Studying calcium reuptake and relaxation mechanisms |
| Patch clamp | Membrane potential and ion channel currents | Investigating hyperpolarization and K+ channels |
| Western blot | Protein expression and phosphorylation | Assessing MYLK, PPP1R12A, and PRKG1 activity |
| cGMP/cAMP assays | Cyclic nucleotide levels | Measuring NO and prostaglandin signaling |
| CRISPR knockout | Gene function loss | Testing causal role of NOS3, PTGS2, etc. |
| RNA-seq | Transcriptome changes | Identifying genes regulated during relaxation |
| Proteomics | Protein abundance and modifications | Discovering novel relaxation regulators |
Organ Bath Myography
Organ bath myography measures isometric force of isolated smooth muscle strips in response to relaxants. This method has been used to assess drotaverine-induced relaxation of airway smooth muscle and adenosine relaxation of vascular smooth muscle. It is a gold-standard technique for quantifying relaxation responses.
Calcium Imaging
Calcium imaging using fluorescent indicators (e.g., Fura-2) measures intracellular calcium concentrations in smooth muscle cells. Since relaxation is driven by reduction in cytosolic calcium, this method is essential for studying SERCA and ryanodine receptor function. It can be combined with pharmacological agents to dissect signaling pathways.
Patch Clamp Electrophysiology
Patch clamp records membrane potential and ion channel activity. Hyperpolarization caused by nitric oxide in arterial smooth muscle was demonstrated using this technique. It is critical for studying potassium channels (e.g., KCNMA1, ABCC9) that mediate relaxation.
Molecular Biology and CRISPR Screening
CRISPR knockout and knock-in models allow causal testing of genes involved in relaxation. For example, NOS3 knockout mice show impaired vasodilation. High-throughput CRISPR library screening can identify novel regulators of smooth muscle relaxation, while RNA-seq and proteomics reveal expression changes.
How CRISPR Can Be Used to Study GO:0044557 relaxation of smooth muscle
Knockout
CRISPR knockout of genes such as NOS3, PTGS2, or ADORA2A in mice or cell models can abolish specific relaxation pathways. For example, NOS3 knockout impairs arterial relaxation, and PTGS2 knockout reduces PGE2-mediated airway relaxation. These models are essential for establishing causality.
Point Mutation
Point mutations can mimic human disease variants or alter protein function. For instance, a point mutation in PRKG1 could affect cGMP binding and NO sensitivity, leading to altered vascular relaxation. Such models help dissect molecular mechanisms.
Knock-in
Knock-in of tagged proteins (e.g., MYLK-GFP) allows real-time visualization of protein localization during relaxation. Knock-in of human disease alleles can model conditions like hypertension or asthma.
Overexpression
Overexpression of relaxation-promoting genes, such as ADORA2A or NOS3, can enhance relaxation responses. Transgenic overexpression models are useful for testing therapeutic potential.
How EDITGENE Supports relaxation of smooth muscle Research
Researchers studying relaxation of smooth muscle-related genes often need to determine whether a candidate gene is causally involved in the process or merely correlated with it. EDITGENE provides a comprehensive suite of CRISPR-based services to enable such causal studies, from knockout to knock-in and overexpression models, as well as high-throughput screening and bioinformatics support.
Contact EDITGENE today to design your custom CRISPR model for relaxation of smooth muscle research.
Frequently Asked Questions About relaxation of smooth muscle
What is GO:0044557 relaxation of smooth muscle?
GO:0044557 is a Gene Ontology biological process term defined as the process in which the extent of smooth muscle contraction is reduced. Smooth muscle differs from striated muscle in its high actin/myosin ratio, absence of conspicuous sarcomeres, and ability to contract to a much smaller fraction of its resting length.
What genes are involved in relaxation of smooth muscle?
Key genes include NOS3, NOS1, PTGS2, ADORA2A, PRKG1, MYLK, PPP1R12A, and KCNMA1, among others. These genes mediate nitric oxide signaling, prostaglandin synthesis, adenosine responses, and calcium regulation.
How is nitric oxide involved in smooth muscle relaxation?
Nitric oxide derived from endothelium or nerves diffuses into smooth muscle cells, causing hyperpolarization and relaxation. It activates soluble guanylate cyclase, leading to cGMP production and protein kinase G activation, which reduces intracellular calcium.
What diseases are associated with impaired smooth muscle relaxation?
Impaired relaxation contributes to asthma, hypertension, urethral obstruction, and ocular hypertension. For example, reduced NO-mediated relaxation leads to hypertension, while defective airway relaxation worsens asthma.
What experimental models are used to study smooth muscle relaxation?
Common models include organ bath myography of isolated smooth muscle strips, calcium imaging, patch clamp electrophysiology, and CRISPR knockout mice (e.g., NOS3 KO). These methods allow quantification of relaxation responses and causal gene testing.
How does prostaglandin E2 relax airway smooth muscle?
Prostaglandin E2, along with pulmonary surfactant, promotes relaxation of airway smooth muscle in human and guinea pig tissues. It acts through G-protein coupled receptors to increase cAMP and reduce calcium sensitivity.
What is the role of adenosine in vascular smooth muscle relaxation?
Adenosine relaxes isolated vascular smooth muscle by activating A2A and A2B receptors, which increase cAMP and lead to relaxation. This contributes to the regulation of blood flow.
Can CRISPR be used to study smooth muscle relaxation?
Yes. CRISPR knockout, knock-in, and overexpression models allow researchers to test the causal role of specific genes in relaxation. For example, NOS3 knockout mice show impaired arterial relaxation.
What is drotaverine and how does it affect smooth muscle?
Drotaverine is a clinically used antispasmodic that relaxes airway smooth muscle. Its relaxant effect has been assessed in experimental models, confirming its direct action on smooth muscle.
How does maturation affect airway smooth muscle relaxation?
Mechanisms of airway smooth muscle relaxation change during maturation, with age-dependent differences in signaling pathways. This has implications for pediatric respiratory diseases.
Conclusion
Relaxation of smooth muscle (GO:0044557) is a vital biological process that regulates the tone of hollow organs and blood vessels. Its dysregulation is implicated in major diseases such as asthma, hypertension, and urogenital disorders. The molecular mechanisms involve nitric oxide, prostaglandins, adenosine, and calcium handling, with key genes like NOS3, PTGS2, and ADORA2A. CRISPR-based models are powerful tools for dissecting these pathways and identifying therapeutic targets. EDITGENE offers comprehensive services to support such research, from knockout to overexpression and screening.
References
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