Hippocampal CA1 pyramidal cell neurons are sensitized to depolarization by l-2-amino-4-phosphonobutanoic acid (l-AP4) following exposure to l-quisqualic acid (QUIS). It has been proposed that induction of this 'QUIS-effect' involves uptake of l-QUIS by hippocampal cells. We have used o-phthaldialdehyde (OPA) derivatization and high performance liquid chromatographic (HPLC) separation of extracts from hippocampal slices which have been exposed to varied concentrations of l-QUIS to investigate l-QUIS uptake into hippocampal slices. We observe uptake rates such that the internal concentration of l-QUIS exceeds the bath concentration within 7 min. The fact that this uptake is concentrative indicates that it is mediated by an active transport system. In addition, uptake of l-QUIS may be linked to the induction of the QUIS-effect. At low concentrations of l-QUIS (< 4 μM), the QUIS-effect is only partially induced within the 4 min incubation time which maximally induces the effect when 16 μM l-QUIS is used. However, repeated 4 min exposure periods of slices to low l-QUIS concentrations will eventually induce the QUIS-effect even when each exposure is separated by extensive washout periods. Hence induction is dependent on both concentration and total exposure time. We also examined the effects of l-α-aminoadipic acid and l-serine-O-sulfate on the rate of l-QUIS uptake. Exposure of slices to these compounds prior to treatment with l-QUIS will block the physiological effects of l-QUIS. We found that these 'pre-blocking' compound did not decrease the rate of l-QUIS uptake. However, like l-QUIS, these compounds undergo uptake and exert their effects in a manner which is dependent on both concentration and total exposure time.
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Acknowledgements. This work was supported by NIH Grant NS17944 and a Grant-in-Aid from the Graduate School of the University of Minnesota. We would like to express our appreciation to Dr. Robert Miller and Dr. Dale Branton for the use of their HPLC system and the valuable advice and assistance they provided.
- 2-Amino-4-phosphonobutanoic acid
- CA1 pyramidal cell
- Excitatory amino acid