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Investigation of bicarbonate independent mechanisms, involved in the secretion of cerebrospinal fluid in rats
Author(s) -
Bouzinova Elena V.,
Aalkjaer Christian,
Praetorius Jeppe
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a764-a
Subject(s) - amiloride , bicarbonate , intracellular ph , sodium–hydrogen antiporter , choroid plexus , chemistry , epithelial sodium channel , epithelial polarity , intracellular , secretion , cerebrospinal fluid , apical membrane , sodium , microbiology and biotechnology , cytosol , endocrinology , medicine , biochemistry , biology , membrane , enzyme , organic chemistry , central nervous system
Cerebrospinal fluid (CSF) is produced with a rate of about 3.4 μl/min in rats (Chodobski et al., 1998) of which the majority is secreted by the choroid plexus epithelium (CP) in the four brain ventricles. The apically localized Na + /K + ATPase mediates the Na + secretion and the driving force for the less well established basolateral Na + uptake into the CP cells. The involvement of Na + /H + exchange (NHE) in CP‐mediated CSF formation has been suggested previously but NHE proteins have not been detected. Thus, we aimed to investigate the importance of bicarbonate independent Na + uptake in intracellular pH regulation in CP using an intracellular fluorescent pH indicator. Amiloride (600 μM), EIPA (50 μM), HOE 694 (10 μM) were used to block NHE. Experiments on enzymatically isolated cells revealed Na + dependent pH i recovery in the absence of HCO 3 − /CO 2 that was sensitive to amiloride (600 μM), whereas the more specific NHE1 blockers EIPA (50 μM), HOE 694 (10 μM) had no effect on pH i recovery. The mRNA encoding NHE1 and NHE8 was detected in rat CP, and at least NHE1 also in an isolated epithelial preparation. The results suggest that Na + /H + exchange in CP may be mediated by NHE1, although the relative insensitivity to NHE inhibitors may suggest the involvement of another NHE. In conclusion, NHE proteins can not be excluded as basolateral Na + entry mechanisms in CP‐mediated CSF secretion.