Are claudin-5 tight-junction proteins in the blood-brain barrier porous?
Abstract
The capillaries of the brain are particularly special, as they are not
simply conduits for blood, but are primarily responsible to ensure that
the neurons function in a strictly regulated homeostatic interstitium.
Brain endothelial cells (BECs) express a plethora of ion channels on its
luminal and abluminal surfaces, namely: potassium (K+
) channels (i.e.,
Kir2 and Kv1), chloride (Cl–)/bicarbonate (HCO3–) channels, as well as a number of ion-solute exchangers (Redzic et al., 2011). These channels essentially prioritize vectorial transendothelial transport, especially for the regulation of K+ flux across the blood-brain barrier (BBB) (Redzic et al., 2011). The differences between the K+ concentration of the brain interstitium and plasma is only 2 mM to 4 mM, but the maintenance of this ionic concentration difference provides a constancy for the neuronal resting membrane potential, their associated firing thresholds and the preservation of a constant level of neuronal excitability.