Cysteine: Depolarization‐Induced Release from Rat Brain In Vitro

Abstract

Compounds released on depolarization in a Ca2+-dependent manner from rat brain slices were screened to identify candidates for neuroactive substances. Lyophilized superfusates were analyzed by reversed-phase HPLC after derivatization with 9-fluorenyl N-succinimidyl carbonate. One of the compounds that showed an increase of concentration in superfusates in the presence of iodoacetamide was identified as the cysteine (Cys) derivative, S-carboxamidomethylcysteine, by fast atom bombardment mass spectrometry and other methods. This stable Cys derivative originates from endogenous, extracellular Cys. The finding led to a method for quantification of Cys in superfusates by immediate cooling of the superfusates to 0 degrees C and reaction of Cys with N-ethylmaleimide. Depolarization-induced Ca2+-dependent release of Cys was most prominent in the neocortex, followed by the mesodiencephalon, striatum, and cerebellum. This suggests that Cys is released from a neuronal compartment and might be involved in neurotransmission.

Screening of Thiol Compounds: Depolarization‐Induced Release of Glutathione and Cysteine from Rat Brain Slices

“…Compared with the previously published data on Cys release (Keller et al, 1989), which are qualitatively similar, our data show some quantitative differences. Under resting conditions, only about one-half to one-third of the concentrations measured by Keller et al (1989) were detected. This discrepancy can be explained partly by the longer equilibration time (50 min) used here to superfuse the slices before collecting samples compared to that used by Keller et al (30 min).…”

“…A large portion of both thiols released was in the reduced form (85-100%). This suggests that not only Cys, which has been reported previously to be released on depolarization (Keller et al, 1989), but also reduced GSH is released from a neuronal compartment and might participate in neuronal transmission. The oxidized portion could result from release of disulfide compounds (cystine, GSSG, mixed disulfides).…”

“…Furthermore, thiol compounds-in particular, cysteine (Cys) and glutathione (GSH) (Li et al, 1954;Li and Manning, 1955)-are good ligands for transition metal ions such as Zn2+ and could therefore have an indirect effect on receptors and channels sensitive to such ions. Our group previously reported a Ca2+-dependent release of Cys from rat brain slices (Keller et al, 1989). In the present study we screened for other sulfhydryl compounds possibly involved in neurotransmission.…”

Sulphur-containing excitatory amino acids in intercellular communication

“…A CaZ+ -dependent K+-induced release of cysteine [7] and of GSH [8] has been demonstrated in various rat brain structures. Although the neuroactivity of cysteine is still under investigation, preliminary results show that cysteine could act on the metabotropic glutamate receptor [ 121.…”

“…Such compounds were then chemically identified and their biological effects as well as their cellular localization investigated. This approach shed a new light on a few sulphur-containing compounds such as HCA and cysteine sulphinic acid (CSA), as well as cysteine [7] and glutathione (GSH) [8]. HCA, an analogue of glutamate, and CSA, an analogue of aspartate, have been recognized as neuroexcitants for more than 30…”