Clonidine inhibits and phorbol acetate activates glutamate release from rat spinal synaptoneurosomes.
Glutamate is a major neural transmitter of noxious stimulation in the spinal cord. We measured glutamate release from rat spinal synaptoneurosomes by using an enzyme-linked fluorimetric assay. Glutamate was released from spinal cord synaptoneurosomes in response to the addition of 30 mM potassium chloride, 1 mM 4-aminopyridine, or 1 microM ionomycin in the presence of external calcium. There was less release of glutamate in the absence, versus the presence, of external calcium. Clonidine significantly reduced the level of glutamate released from the spinal cord synaptoneurosomes. Tetradecanoyl phorbol acetate, an activator of protein kinase C, enhanced glutamate release. Forskolin, a protein kinase A activator, had no effect on the glutamate efflux. Our data indicate that glutamate released in the spinal cord is dependent on protein kinase C but is independent of the protein kinase A pathway. They also suggest that the inhibition of glutamate release may be the underlying mechanism of antinociception by clonidine at the spinal cord level.


CONCLUSIONS
We demonstrated that synaptoneurosomes from rat spinal cord could release glutamate in response to depolarization. We showed that an activator of protein kinase C increased glutamate released from spinal cord synaptoneurosomes but that clonidine decreased it. Glutamate release may be one of the mechanisms of antinociception at the spinal cord level.
Shinomura
T
T
Department of Anesthesia, Kyoto University Hospital, Japan. shino@kuhp.kyoto-u.ac.jp
Nakao
S
S
Adachi
T
T
Shingu
K
K
D015761:4-Aminopyridine / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D003000:Clonidine / Q000494:pharmacology*; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D005969:Glutamate Dehydrogenase / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D011189:Potassium Chloride / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013050:Spectrometry, Fluorescence; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D005576:Colforsin; D018698:Glutamic Acid; D011189:Potassium Chloride; D015761:4-Aminopyridine; D005969:Glutamate Dehydrogenase; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D003000:Clonidine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium