Visceral smooth muscle (VSM)

Visceral smooth muscle, also known as single-unit smooth muscle, is a type of non-striated muscle found in the walls of hollow internal organs such as the stomach, intestines, bladder, and uterus (StatPearls, 2023, NBK526125). Unlike multi-unit smooth muscle, the cells in visceral smooth muscle are connected by gap junctions, allowing them to contract as a single coordinated unit or functional syncytium (Britannica, 2024). Its primary biological function is to facilitate involuntary movements like peristalsis and the regulation of organ volume through sustained, rhythmic contractions (NIH, 2022). In clinical pharmacology, this tissue is not a single molecular target but rather a physiological site containing various receptors, such as muscarinic and adrenergic receptors, and ion channels like L-type calcium channels (PubMed, 2021, PMC8143845). Drugs targeting these components are used to treat conditions like overactive bladder, irritable bowel syndrome, and asthma. Because these receptors are often expressed across multiple organ systems, therapeutic intervention can lead to systemic safety concerns such as hypotension, dry mouth, or gastrointestinal distress.

Other names

Unitary smooth muscleSingle-unit smooth muscleInvoluntary muscle

Pharmacological agents typically modulate visceral smooth muscle tone by acting as agonists or antagonists on G protein-coupled receptors (such as muscarinic M3 or adrenergic beta-2 receptors) or by blocking voltage-gated calcium channels to influence intracellular calcium concentrations and subsequent cross-bridge cycling.