Cytotoxic actions and effects on intracellular Ca2+ and cGMP concentrations of sulphur-containing excitatory amino acids in cultured cerebral cortical neurons

Abstract

Effects of the sulphur-containing acidic amino acids (SAAs) cysteic acid (CA), homocysteic acid (HCA), cysteine sulphinic acid (CSA), homocysteine sulphinic acid (HCSA), and S-sulphocysteine (SC) on intracellular concentrations of Ca2+ ([Ca2+]i) and cGMP ([cGMP]i) as well as their cytotoxic actions were investigated in cultured cerebral cortical neurons. The glutamate receptor subtype selective antagonists APV (D-(-)-2-amino-5-phosphonopentanoate) acting on N-methyl-D-aspartate (NMDA) receptors and DNQX (6,7-dinitroquinoxaline-2,3-dione) acting on non-NMDA receptors were employed to obtain information about the involvement of glutamate receptor subtypes in these actions of the SAAs. It was found that all SAAs exerted a cytotoxic action on the neurons. The ED50 values for CSA, CA, HCSA, and HCA were around 30 to 50 microM and that for SC was about 150 microM. The glutamate transport blocker L-aspartate-beta-hydroxamate increased the efficacy of CSA and CA but had no effect on the cytotoxic actions of the remaining SAAs. In case of CA, HCA, and SC the cytotoxicity could be prevented by APV alone and for HCSA, DNQX could block the toxic action. DNQX reduced the toxicity of HCA somewhat but the presence of APV was required for complete protection. CSA toxicity could only be blocked by the combination of APV and DNQX. All SAAs induced an increase in [cGMP]i and [Ca2+]i and with regard to [Ca2+]i SC was the most potent and CA the least potent SAA. The effect of all SAAs on [cGMP]i could be blocked by APV alone whereas DNQX had no effect except in the case of HCSA where the response was blocked completely and HCA where the response was inhibited by 75%.(ABSTRACT TRUNCATED AT 250 WORDS)