veratrine and homocysteic-acid

A potassium-induced, calcium-dependent release of endogenous homocysteic acid (HCA) from rat striatal slices was demonstrated. A precolumn derivatization high-performance liquid chromatography method was developed that allowed quantitative determination of sulfur-containing amino acids at the picomole level. Intracellular recordings from cat caudate neurons during simultaneous microiontophoretic application of drugs and electrical stimulation of the corticocaudate pathway showed that (L)-HCA evoked a depolarization pattern similar to that induced by N-methyl-(D)-aspartic acid (NMDA), and both these depolarizations could be selectively inhibited by a specific NMDA antagonist, (D)-2-amino-7-phosphonoheptanoic acid [(D)-AP-7]. A selective antagonism of (L)-HCA-induced depolarizations by (D)-AP-7 was confirmed in quantitative experiments with the frog hemisected spinal cord in vitro. Small quantities of iontophoretically applied (L)-HCA, but not of quisqualate, potentiated cortically evoked EPSPs in cat caudate neurons. These observations suggest that (L)-HCA might be a candidate as an NMDA-receptor-preferring endogenous transmitter in the caudate nucleus. One possible function for such transmitter systems could be the enhancement of EPSPs.

Topics: Animals; Aspartic Acid; Calcium; Cats; Caudate Nucleus; Chromatography, High Pressure Liquid; Corpus Striatum; Drug Synergism; Electric Stimulation; Electrophysiology; Evoked Potentials; Glutamates; Glutamic Acid; Homocysteine; Iontophoresis; Oxadiazoles; Potassium; Quisqualic Acid; Rana temporaria; Rats; Veratrine

Efflux of various amino acids from rat brain slices was determined under resting or depolarizing conditions. Slices of neocortex, hippocampus, striatum, cerebellum, mesodiencephalon, pons-medulla, and spinal cord were depolarized by K+ (50 mM) or veratrine (33 micrograms/ml). The 4-N,N-dimethylamino-azobenzene-4'-isothiocyanate (DABITC) derivatization method of Chang [Biochem. J. 199, 537-545 (1981)] for HPLC was adapted for analysis of amino acids and peptides in superfusion solutions. It allowed the separation and simultaneous detection of the sulfur-containing amino acids cysteine sulfinic acid (CSA), cysteic acid (CA), homocysteine sulfinic acid (HCSA), and homocysteic acid (HCA) at the picomole level. All four were shown to be released on depolarization in a Ca2+-dependent manner from brain slices. CSA and HCSA were released from cortex, hippocampus, mesodiencephalon, and, for HCSA only, striatum. HCA release, observed in all regions, was most prominent in cortex and hippocampus. CA was slightly increased by depolarization in hippocampus and mesodiencephalon. These sulfur-containing amino acids have been shown to exert an excitatory action on CNS neurons. The fact that these sulfur-containing amino acids are released as endogenous substances from nervous tissue supports the hypothesis that they play a role in CNS neurotransmission.

Topics: Amino Acids, Sulfur; Animals; Brain; Cysteic Acid; Cysteine; Homocysteine; In Vitro Techniques; Male; Neurotransmitter Agents; Potassium; Rats; Tissue Distribution; Veratrine