Vasomotion is the spontaneous oscillation in tone of

blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...

walls, independent of heart beat,

innervation A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellula ...

. While vasomotion was first observed by

Thomas Wharton Jones Thomas Wharton Jones (9 January 1808 – 7 November 1891) was an eminent ophthalmologist and physiologist of the 19th century. Biography Jones's father was Richard Jones, a native of London. Richard Jones had moved north to St. Andrews and was ...

in 1852, the complete mechanisms responsible for its generation and its physiological importance remain to be elucidated, however several hypotheses have been put forth.

Mechanism

Intracellular

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

(Ca²⁺) concentration exhibits periodic oscillations in vascular

smooth muscle Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...

cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

s. This is thought to result from Ca²⁺ release from intracellular stores, due to

inositol triphosphate Inositol trisphosphate or inositol 1,4,5-trisphosphate abbreviated InsP3 or Ins3P or IP3 is an inositol phosphate signaling molecule. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the p ...

and

ryanodine Ryanodine is a poisonous diterpenoid found in the South American plant ''Ryania speciosa'' (Salicaceae). It was originally used as an insecticide. The compound has extremely high affinity to the open-form ryanodine receptor, a group of calcium ch ...

-sensitive channel activation. This activation has been shown to result in either Ca²⁺ "sparks", highly localized calcium increases, or "waves", global Ca²⁺ increase that propagates the length of the cell. To allow vasomotion to occur, synchronization must occur between the individual oscillations, resulting in global calcium synchronization and vessel tone oscillation.Nilsson H, Aalkjaer C. Vasomotion: mechanisms and physiological importance. Molecular Interventions. 2003; 3: 79-89.

Gap junction Gap junctions are specialized intercellular connections between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulate ...

s are thought to play a large role in this synchronization, as application of gap junction blockers has been shown to abolish vasomotion, indicating a critical role. Due to regional variations in gap junction distribution and coupling (homocellular vs. heterocellular) several hypotheses have been suggested to account for vasomotion occurrence. The "classic" mechanism of vasomotion generation is thought to be the voltage-dependent coupled model. In this model, high gap junction coupling is present between the vascular smooth muscle cells, the

endothelial The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...

cells and the endothelial to vascular smooth muscle cells. An initial depolarizing current leads to the opening of the voltage-dependent calcium channels, ultimately resulting in synchronization of individual calcium levels. When patch clamp recordings are conducted, depolarization occurs in the endothelial layer at the same time as the underlying vascular smooth muscle. The cause of the initial depolarizing current, however, remains to be determined. Mathematical modeling has pointed to the existence of 2-4 independent non-linear oscillating systems interacting to produce vasomotion. It is possible that in order for vasomotion to be generated, these systems must pass a depolarizing threshold.

Physiological role

Several possible hypotheses have been advanced to explain vasomotion. Increased flow is one possibility; mathematical modeling has shown a vessel with an oscillating diameter to conduct more flow than a vessel with a static diameter. Vasomotion could also be a mechanism of increasing the reactivity of a blood vessel by avoiding the "latch state", a low ATP cycling state of prolonged force generation common in vascular smooth muscle. Finally, vasomotion has been shown to be altered in a variety of pathological situations, with vessels from both

hypertensive Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...

and

diabetic Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level (hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased app ...

patients displaying altered flow patterns as compared to normotensive vessels.Gratton RJ, Gandley RE, McCarthy JF, Michaluk WK, Slinker BK, McLaughlin MK. Contribution of vasomotion to vascular resistance: a comparison of arteries from virgin and pregnant rats. J Appl Physiol. 1998; 85: 2255-2260.

References

{{Cardiovascular physiology Angiology Circulatory system

Mechanism

Physiological role

See also

References