Sulfhydryl groups essential for the volume-sensitive release of taurine from astrocytes.
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 IC50 of 54 microM. 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.
Institute of Cell Physiology, National University of Mexico, Mexico City.
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A
Martínez
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Muñoz-Clares
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G
Guerra
J
J
Morán
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Pasantes-Morales
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism; D003470:Culture Media; D004594:Electrophysiology; D005033:Ethylmaleimide / Q000494:pharmacology; D007700:Kinetics; D051381:Rats; D013438:Sulfhydryl Compounds / Q000494:pharmacology*; D013654:Taurine / Q000378:metabolism*
D003470:Culture Media; D013438:Sulfhydryl Compounds; D013654:Taurine; D005033:Ethylmaleimide