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Sulfhydryl groups essential for the volume-sensitive release of taurine from astrocytes

Authors
Journal
Neuroscience Letters
0304-3940
Publisher
Elsevier
Publication Date
Volume
176
Issue
2
Identifiers
DOI: 10.1016/0304-3940(94)90091-4
Keywords
  • Taurine
  • Nem
  • Mercurial Reagent
  • Volume Regulation
  • Pcmbs
  • Mersalyl

Abstract

Abstract The volume-sensitive [ 3H]taurine efflux from cultured astrocytes was found to be strongly inhibited by the sulfhydryl group-modifying reagent N-ethylmaleimide (NEM). This maleimide inhibited taurine efflux evoked by 50% hyposmotic solutions with an IC 50 of 54 μM. The inhibition by NEM followed pseudo-first order reaction kinetics. A double log plot of the pseudo-first order constant against NEM concentration gave a linear relationship with a slope of 1.2. The data are consistent with a simple bimolecular reaction mechanism in which one molecule of NEM reacts with one sulfhydryl group per transport unit. The membrane-impermeant maleimide derivative 5-eosin maleimide did not affect the volume-stimulated taurine efflux. The sulfhydryl-modifying mercurial reagents mersalyl and p-chloro mercuribenzenesulfonate (0.5–1 mM) increased [ 3H]taurine efflux under isosmotic conditions and concomitantly decreased the hyposmolarity-evoked efflux. The results demonstrate an essential requirement for sulfhydryl groups for the volume-sensitive taurine efflux.

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