Regulatory volume increase in epithelial cells isolated from the mouse fourth ventricle choroid plexus involves Na+–H+ exchange but not Na+–K+–2Cl− cotransport

The aim of this study was to determine the ability of choroid plexus epithelial cells to volume regulate when exposed to hypertonic solutions, and furthermore to identify the ion transporters involved in any volume regulation. Experiments were performed on cells freshly isolated, using the enzyme dispase, from the mouse fourth ventricle choroid plexus. Cell volume was measured using a video-imaging method. Cells used in this study were all of a similar morphology and had a mean volume of 0.71 pl. Cells shrank when superfused with hypertonic solutions to a minimum relative cell volume of 0.84 ± 0.01 (n = 8) in 3 min. They then exhibited a regulatory volume increase (RVI) to reach a relative volume of 0.92 ± 0.02 over the following 12 min. The RVI was HCO3−-dependent, that is it was not observed in hepes-buffered solutions. A post-regulatory volume decrease RVI (post-RVD RVI) was also observed in cells following exposure to hypotonic solutions. The RVI and post-RVD RVI were inhibited by 10 µM 5-(N-ethyl-N-isopropyl) amiloride or 10 μM 5-(N-methyl-N-isobutyl) amiloride, both selective inhibitors of Na+–H+ exchange (NHE). They were also inhibited by the anion transport inhibitor 100 µM 2,2′-(1,2-ethenediyl) bis (5-isothiocyanatobenzenesulfonic acid). The Na+–K+–2Cl− cotransporter inhibitor, 10 µM bumetanide, was without effect on either the RVI or the post-RVD RVI. The data indicate that NHE, probably in combination with Cl−–HCO3− exchangers, contributes to RVI in choroid plexus epithelial cells.