Topiramate Affects the Ability of cAMP-Activated Protein Kinase to Phosphorylate Glutamate Receptors Activated by Kainate.
Abstract number :
1.022
Submission category :
Year :
2001
Submission ID :
2730
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
M. ängehagen, M.Sc., Institute of Clinical Neuroscience, Göteborg, Sweden; R. Shank, Ph.D., The RW Johnson Pharmaceutical Research Institute, Spring House, PA; E. Hansson, Ph.D., Institute of Clinical Neuroscience, Göteborg, Sweden; L. Rönnbäck, M.D., Ph.
RATIONALE: The antiepileptic drug topiramate (TPM) is known to have several mechanisms of action, one being an allosteric inhibition of kainate/AMPA receptors. The mechanism of this inhibition is not known, but it has been postulated that TPM may bind to AMPA/kainate receptors at sites phosphorylated by cAMP-activated protein kinase (PKA). This hypothesis stipulates that TPM can bind to these sites only in the dephosphorylated state, and predicts that the activity of TPM should be inversely related to the level of PKA activation. To test this hypothesis we examined the effects of a PKA activator (forskolin) and inhibitor (H89) on the ability of TPM to inhibit kainate-induced increases in intracellular Ca2+.
METHODS: The study was conducted using mixed neuronal/astroglial primary cortical cultures from rat pups, and kainate-induced changes in [Ca2+][sub]i[/sub] were monitored with the Ca2+ sensitive probe fura-2/AM using a micro-spectrofluorometric imaging system. Kainate (100 [mu]M) was bath applied to the cells after pretreatment with TPM (100 [mu]M), forskolin (10 [mu]M) or H89 (5 [mu]M).
RESULTS: TPM alone reduced the kainate-induced [Ca2+][sub]i[/sub] response by 30% (P[lt]0.001). Pretreatment with forskolin alone enhanced the [Ca2+][sub]i[/sub] response by 39% (P[lt]0.05). A combination of forskolin and TPM did not significantly affect the kainate-induced [Ca2+][sub]i[/sub] response. Pretreatment with H89 reduced the kainate-induced [Ca2+][sub]i[/sub] response by 63% (P[lt]0.001), and simultaneous exposure to both H89 and TPM reduced the [Ca2+][sub]i[/sub] response by 82 % (P[lt]0.05 when compared to H89 alone).
CONCLUSIONS: The results show that under our experimental conditions TPM inhibits PKA modulation of kainate-induced changes in [Ca2+][sub]i[/sub]. Conclusive proof of the hypothesis will require a demonstration that TPM selectively interacts with kainate/AMPA receptor sites sensitive to PKA-induced phosphorylation.
Support: The RW Johnson Pharmaceutical Research Institute., Spring House PA 19477, USA.