Osmotically induced volume changes of freshly isolated rat fflppocampal neurons
We isolated CA1 pyramidal cells (Kay & Wong, J. Neurosci. Meth. 16: 227-238, 1986) and measured il volume during changes of extracellular osmolarity (πo) as follows. (1) The image of cells filled with dye PBFI or SBFI was captured by computer and the volume of a sphere having equivalent distribution of fluorescence intensities (at isosbestic 380 nm excitation) computed. Or, (2) cells in a flow cell of 70 μ1 volume were imaged in white light and volume changes were computed as the change of the 3rd power of the normalized transverse radius. π0 was lowered by deleting NaCl from the bathing fluid and raised by adding mannitol, exposure times were 3, 5 or 30 minutes. When πO was reduced by 40-50 mOsm for 3-5 min, cells swelled on average by 15%; with πO increased by 50 mOsm cells shrank by 11%; but responses varied at AπO -50 mOsm (5 min) from 0% to 55% and at AπO -120 mOsm (3 min) from 4% to 141%. The onset of swelling was frequently delayed by several minutes from the start of hypotonie exposure. The resistance of some neurons to swelling could be explained either by limited water permeability, or by mechanical support of the plasma membrane by the cytoskeleton. Such a mechanism could protect neurons against swelling-induced damage.
Somjen, GG; Wadman, WJ; Juta, A; Borplorf, A; Aitken, PO; Kiehart, PP
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