Vasomotion
Encyclopedia
Vasomotion is the spontaneous oscillation in tone of blood vessel
s, independent of heart beat
, innervation
or respiration
. While vasomotion was first observed by Jones in 1852, the complete mechanisms responsible for its generation and its physiological importance remain to be elucidated, however several hypothesis have been put forth.
(Ca2+) concentration exhibits periodic oscillations in vascular smooth muscle
cell
s, this is thought to be due Ca2+ release from intercellular stores due to inositol tri-phosphate and ryanodine 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.
Gap junction
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 hypothesis 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
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 endothlial 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.
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
and diabetic
patients displaying altered flow patterns as compared to normotensive vessels.
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s, independent of heart beat
Cardiac cycle
The cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next. The frequency of the cardiac cycle is described by the heart rate. Each beat of the heart involves five major stages...
, innervation
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
or respiration
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
. While vasomotion was first observed by Jones in 1852, the complete mechanisms responsible for its generation and its physiological importance remain to be elucidated, however several hypothesis have been put forth.
Mechanism
Intercellular calciumCalcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
(Ca2+) concentration exhibits periodic oscillations in vascular smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s, this is thought to be due Ca2+ release from intercellular stores due to inositol tri-phosphate and ryanodine 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.
Gap junction
Gap junction
A gap junction or nexus is a specialized intercellular connection between a multitude of animal cell-types. It directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells....
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 hypothesis 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
Endothelium
The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart...
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 endothlial 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 hypothesis 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 then 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 ATPAdenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
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
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
and diabetic
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
patients displaying altered flow patterns as compared to normotensive vessels.
See also
- VasoconstrictionVasoconstrictionVasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in...
- VasodilationVasodilationVasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...
- VasospasmVasospasmVasospasm refers to a condition in which blood vessels spasm, leading to vasoconstriction. This can lead to tissue ischemia and death . Cerebral vasospasm may arise in the context of subarachnoid hemorrhage. Symptomatic vasospasm or delayed cerebral ischemia is a major contributor to...