Fig. 5.

Transporter-mediated transport of water against an osmotic gradient. These experiments demonstrate that a sudden addition of KCl leads to an immediate inwardly-directed flux of water that proceeds against the osmotic gradient. In contrast, osmotic challenges by NaCl and mannitol, or KCl plus inhibitors of cotransporters elicit a simple osmotic shrinkage. A Cell volume changes recorded with ion-sensitive microelectrodes in salamander choroid plexus exposed to an osmotic challenge of 100 mOsm mannitol, NaCl, or KCl, as indicated in the figure. B Cell volume changes recorded with an osmotic challenge of 100 mOsm KCl with inclusion of furosemide (frusemide, 100 µM). Figure from [125] with permission. C Volume changes recorded in calcein-AM-loaded mouse choroid plexus challenged with a 100 mOsm gradient of mannitol (M), indicated by the bars. D Choroid plexus challenged with a 100 mOsm gradient of first mannitol (M), then NaCl. E Choroid plexus challenged with a 100 mOsm gradient of first mannitol (M), then KCl. F Choroid plexus challenged with 100 mOsm KCl in the presence of 10 µM bumetanide (n = 6 of each). Figure adapted from [146]