Microelectrodes for measurement of intracellular [K+] and [Na+]in the choroid plexus epithelium and cerebrospinal fluid

Abstract

The choroid plexus epithelium (CPE) has recently gained increasing interest as a potential target tissue to manipulating cerebrospinal fluid (CSF) production (1). It is therefore crucial to identify the basolateral Na+ transport mechanisms that are involved in CSF secretion, as it would be accessible from the blood side and thereby hold promise for pharmacological intervention. The sodium‐bicarbonate transporter Ncbe has been identified as a basolateral Na+ importer in the CPE (2,3). Currently, there is no direct intracellular cation measurements in choroid plexus and this information is needed to establish Ncbe as the main basolateral Na+ importer. The aim of this project is to measure the [Na+] and [K+] concentration in CSF and in CPE in vivo with double‐barreled microelectrodes. Ion selective double‐barreled microelectrodes are the tool to measure directly the different ion concentrations. The reference barreled was filled with 500 mM KCl solution and the tip of ion sensitive barrel was filled with Na+ or K+ionophore and then backfilled with KCl solution. In this ongoing project, we were able to estimate extracellular [K+] to 4.08 ± 1.06 mM in CSF of mice in vivo (n=7). The study is in progress.References1: Damkier HH, Brown PD, Praetorius J. Cerebrospinal fluid secretion by the choroid plexus. Physiol Rev. 2013;93:1847‐92.2: Praetorius J, Nejsum LN, Nielsen S. A SLC4A10 gene product maps selectively to the basolateral plasma membrane of choroid plexus epithelial cells. Am J Physiol Cell Physiol. 2004;286:C601‐10.3: Damkier HH, Nielsen S, Praetorius J. Molecular expression of SLC4‐derived Na+‐dependent anion transporters in selected human tissues. Am J Physiol Regul Integr Comp Physiol. 2007;293:R2136‐46.