Efflux of Osmolyte Amino Acids during Isovolumic Regulation in Hippocampal Slices

Authors

Rodrigo Franco, Universidad Nacional Autónoma de MéxicoFollow
Octavio Quesada, Universidad Nacional Autónoma de México
Herminia Pasantes-Morales, Universidad Nacional Autónoma de MéxicoFollow

Date of this Version

5-23-2000

Citation

Published in Journal of Neuroscience Research 61:6 (September 2000), pp. 701–711; doi: 10.1002/1097-4547(20000915)61:63.0.CO;2-T.

Comments

Copyright © 2000 Wiley-Liss, Inc. Used by permission.

Abstract

The efflux of potassium (K⁺) and amino acids from hippocampal slices was measured after sudden exposure to 10% (270 mOsm), 25% (225 mOsm) or 50% (150 mOsm) hyposmotic solutions or after gradual decrease (22.5 mOsm/min) in external osmolarity. In slices suddenly exposed to 50% hyposmotic solutions, swelling was followed by partial (74%) cell volume recovery, suggesting regulatory volume decrease (RVD). With gradual hyposmotic changes, no increase in cell water content was observed even when the solution at the end of the experiment was 50% hyposmotic, showing the occurrence of isovolumic regulation (IVR). The gradual decrease in osmolarity elicited the efflux of ³H-taurine with a threshold at –5 mOsm and D-[³H]aspartate (as marker for glutamate) and at –20 mOsm for [³H]GABA. The efflux rate of [³H]taurine was always notably higher than those of [³H]GABA and D-[³H]aspartate, with a maximal increase over the isosmotic efflux of about 7-fold for [³H]taurine and 3- and 2-fold for [³H]GABA and D-[³H]aspartate, respectively. The amino acid content in slices exposed to 50% hyposmotic solutions (abrupt change) during 20 min decreased by 50.6% and 62.6% (gradual change). Taurine and glutamate showed the largest decrease. An enhancement in ⁸⁶Rb efflux and a corresponding decrease in K⁺ tissue content was seen in association with RVD but not with IVR. These results demonstrate the contribution of amino acids to IVR and indicate their involvement in this mechanism of cell volume control.