The V-ATPase is expressed in the choroid plexus and mediates cAMP-induced intracellular pH alterations

TY - JOUR

T1 - The V-ATPase is expressed in the choroid plexus and mediates cAMP-induced intracellular pH alterations

AU - Christensen, Henriette L

AU - Păunescu, Teodor G

AU - Matchkov, Vladimir

AU - Barbuskaite, Dagne

AU - Brown, Dennis

AU - Damkier, Helle H

AU - Praetorius, Jeppe

N1 - © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

PY - 2017/1/1

Y1 - 2017/1/1

N2 - The cerebrospinal fluid (CSF) pH influences brain interstitial pH and, therefore, brain function. We hypothesized that the choroid plexus epithelium (CPE) expresses the vacuolar H+-ATPase (V-ATPase) as an acid extrusion mechanism in the luminal membrane to counteract detrimental elevations in CSF pH. The expression of mRNA corresponding to several V-ATPase subunits was demonstrated by RT-PCR analysis of CPE cells (CPECs) isolated by fluorescence-activated cell sorting. Immunofluorescence and electron microscopy localized the V-ATPase primarily in intracellular vesicles with only a minor fraction in the luminal microvillus area. The vesicles did not translocate to the luminal membrane in two in vivo models of hypocapnia-induced alkalosis. The Na+-independent intracellular pH (pHi) recovery from acidification was studied in freshly isolated clusters of CPECs. At extracellular pH (pHo) 7.4, the cells failed to display significant concanamycin A-sensitive pHi recovery (i.e., V-ATPase activity). The recovery rate in the absence of Na+ amounted to <10% of the pHi recovery rate observed in the presence of Na+. Recovery of pHi was faster at pHo 7.8 and was abolished at pHo 7.0. The concanamycin A-sensitive pHi recovery was stimulated by cAMP at pH 7.4 in vitro, but intraventricular infusion of the membrane-permeant cAMP analog 8-CPT-cAMP did not result in trafficking of the V-ATPase. In conclusion, we find evidence for the expression of a minor fraction of V-ATPase in the luminal membrane of CPECs. This fraction does not contribute to enhanced acid extrusion at high extracellular pH, but seems to be activated by cAMP in a trafficking-independent manner.

AB - The cerebrospinal fluid (CSF) pH influences brain interstitial pH and, therefore, brain function. We hypothesized that the choroid plexus epithelium (CPE) expresses the vacuolar H+-ATPase (V-ATPase) as an acid extrusion mechanism in the luminal membrane to counteract detrimental elevations in CSF pH. The expression of mRNA corresponding to several V-ATPase subunits was demonstrated by RT-PCR analysis of CPE cells (CPECs) isolated by fluorescence-activated cell sorting. Immunofluorescence and electron microscopy localized the V-ATPase primarily in intracellular vesicles with only a minor fraction in the luminal microvillus area. The vesicles did not translocate to the luminal membrane in two in vivo models of hypocapnia-induced alkalosis. The Na+-independent intracellular pH (pHi) recovery from acidification was studied in freshly isolated clusters of CPECs. At extracellular pH (pHo) 7.4, the cells failed to display significant concanamycin A-sensitive pHi recovery (i.e., V-ATPase activity). The recovery rate in the absence of Na+ amounted to <10% of the pHi recovery rate observed in the presence of Na+. Recovery of pHi was faster at pHo 7.8 and was abolished at pHo 7.0. The concanamycin A-sensitive pHi recovery was stimulated by cAMP at pH 7.4 in vitro, but intraventricular infusion of the membrane-permeant cAMP analog 8-CPT-cAMP did not result in trafficking of the V-ATPase. In conclusion, we find evidence for the expression of a minor fraction of V-ATPase in the luminal membrane of CPECs. This fraction does not contribute to enhanced acid extrusion at high extracellular pH, but seems to be activated by cAMP in a trafficking-independent manner.

U2 - 10.14814/phy2.13072

DO - 10.14814/phy2.13072

M3 - Journal article

C2 - 28053225

SN - 2051-817X

VL - 5

JO - Physiological Reports

JF - Physiological Reports

IS - 1

M1 - e13072

ER -