Mechanisms of cerebrospinal fluid secretion by the choroid plexus epithelium: Application to various intracranial pathologies

Abstract

The choroid plexus (CP) is a small yet highly active epithelial tissue located in the ventricles of the brain. It secretes most of the CSF that envelops the brain and spinal cord. The epithelial cells of the CP have a high fluid secretion rate and differ from many other secretory epithelia in the organization of several key ion transporters. One striking difference is the luminal location of, for example, the vital Na⁺-K⁺-ATPase. In recent years, there has been a renewed focus on the role of ion transporters in CP secretion. Several studies have indicated that increased membrane transport activity is implicated in disorders such as hydrocephalus, idiopathic intracranial hypertension, and posthemorrhagic sequelae. The importance of the CP membrane transporters in regulating the composition of the CSF has also been a focus in research in recent years, particularly as a regulator of breathing and hemodynamic parameters such as blood pressure. This review focuses on the role of the fundamental ion transporters involved in CSF secretion and its ion composition. It gives a brief overview of the established factors and controversies concerning ion transporters, and finally discusses future perspectives related to the role of these transporters in the CP epithelium.

Keywords: blood‐cerebrospinal fluid barrier; cerebrospinal fluid composition; cerebrospinal fluid pH; cerebrospinal fluid secretion; choroid plexus epithelium; ion transporters.

FIGURE 1

Schematic presentation of the ion contents of cerebrospinal fluid (CSF), choroid plexus epithelial cells (CPEC), and plasma in the rat (Johanson et al., 1992).

FIGURE 2

Schematic presentation of choroid plexus epithelial cells (CPEC), showing characteristic basolateral interdigitations facing the fenestrated capillaries and the cell contacts at the luminal cerebrospinal fluid (CSF)‐facing side, cell–cell contacts indicating proper polarization of the epithelial cell. Ion transporters involved in CSF secretion across the CPEC membranes are shown. Please see the text for details.

FIGURE 3

Schematic presentation of a selection of the transporters involved in pH regulation in the choroid plexus (CP). Please see the text for details.