Fluid and ion transfer across the blood-brain and blood-cerebrospinal fluid barriers; a comparative account of mechanisms and roles

Autor: Stephen B. Hladky, Margery A. Barrand
Rok vydání: 2016
Předmět:
0301 basic medicine
Bicarbonate transport
Hydrostatic pressure
Choroid plexus
Review
Astrocyte endfeet
Sodium transport
Potassium regulation
0302 clinical medicine
Electroneutrality
Transcellular
Cerebrospinal Fluid
Chemistry
Brain
General Medicine
medicine.anatomical_structure
Neurology
Biochemistry
Blood-Brain Barrier
pH regulation
Paracellular transport
Ion channels
Brain interstitial fluid
Neurovascular unit
Chloride transport
Ion transporters
Blood–brain barrier
Endothelial
03 medical and health sciences
Cellular and Molecular Neuroscience
Developmental Neuroscience
Interstitial fluid
Water channels
Transcellular transport
medicine
Fluid secretion
Animals
Humans
Tight junctions
Ion transporter
Ion Transport
030104 developmental biology
Biophysics
Potassium transport
Epithelial
030217 neurology & neurosurgery
Zdroj: Fluids and Barriers of the CNS
ISSN: 2045-8118
Popis: The two major interfaces separating brain and blood have different primary roles. The choroid plexuses secrete cerebrospinal fluid into the ventricles, accounting for most net fluid entry to the brain. Aquaporin, AQP1, allows water transfer across the apical surface of the choroid epithelium; another protein, perhaps GLUT1, is important on the basolateral surface. Fluid secretion is driven by apical Na+-pumps. K+ secretion occurs via net paracellular influx through relatively leaky tight junctions partially offset by transcellular efflux. The blood–brain barrier lining brain microvasculature, allows passage of O2, CO2, and glucose as required for brain cell metabolism. Because of high resistance tight junctions between microvascular endothelial cells transport of most polar solutes is greatly restricted. Because solute permeability is low, hydrostatic pressure differences cannot account for net fluid movement; however, water permeability is sufficient for fluid secretion with water following net solute transport. The endothelial cells have ion transporters that, if appropriately arranged, could support fluid secretion. Evidence favours a rate smaller than, but not much smaller than, that of the choroid plexuses. At the blood–brain barrier Na+ tracer influx into the brain substantially exceeds any possible net flux. The tracer flux may occur primarily by a paracellular route. The blood–brain barrier is the most important interface for maintaining interstitial fluid (ISF) K+ concentration within tight limits. This is most likely because Na+-pumps vary the rate at which K+ is transported out of ISF in response to small changes in K+ concentration. There is also evidence for functional regulation of K+ transporters with chronic changes in plasma concentration. The blood–brain barrier is also important in regulating HCO3 − and pH in ISF: the principles of this regulation are reviewed. Whether the rate of blood–brain barrier HCO3 − transport is slow or fast is discussed critically: a slow transport rate comparable to those of other ions is favoured. In metabolic acidosis and alkalosis variations in HCO3 − concentration and pH are much smaller in ISF than in plasma whereas in respiratory acidosis variations in pHISF and pHplasma are similar. The key similarities and differences of the two interfaces are summarized.
Databáze: OpenAIRE
Externí odkaz: