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Effects of Valproate on K+‐Evoked Serotonin Release and Intracellular Ca 2+ Elevation in Rat Hippocampus.
Author(s) -
Murakarni Takuya,
Okada Motohiro,
Kawata Yuko,
Mizuno Kazuhisa,
Wada Kazumaru,
Kancko Sunao
Publication year - 2000
Publication title -
epilepsia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.687
H-Index - 191
eISSN - 1528-1167
pISSN - 0013-9580
DOI - 10.1111/j.1528-1157.2000.tb02231.x
Subject(s) - chemistry , hippocampal formation , hippocampus , neurotransmitter , biophysics , intracellular , endocrinology , medicine , analytical chemistry (journal) , biochemistry , biology , chromatography , receptor
Purpose : Several investigations have suggested that voltagescnsitive Ca + channcl (VSCC) subtypes activities modulate seizure threshold. In addition, it is well established that presynaptic VSCC activity regulates the releases of neurotransmitters. We have already demonstrated that several types of inonoamine (MA) releases are regulated by N‐, P‐, and Q‐type VSCC subtypes. Specifically, our findings have shown that basal and Ca 2 ‐evoked MA rclease arc rcgulated by N‐type VSCC, whereas K+‐evoked MA rclcase is regulated by P/Q‐ type VSCC. Therefore, to clarify the mechanisms of anticpileptic action of valproate (VPA), the present study determined the effect of VPA on K+‐evoked hippocampal neurotransmitter rclease and intracellular Ca 2+ mobilization. Methods : To study thc elfects of VPA (700pM or 3.5inM) on K+‐evoked (SO and 100 mM) elevation of intraccllular Ca 2+ levels, we prepared the rat hippocampal brain sliccs (350 pm thick) loaded with 100 pM Fura‐2/AM. lntracellular Ca 2+ levels were determined using fluorescence microscopy with digital fluorescencc analyzer system. The microscope was equipped with a computer‐driven interfcrence filter cxchange system, and 340 or 380 nm filters were usc for measurement. Then, 3401380 nm fluorescence ratio was calculated by tligital fluorescence analyzer (Argus‐50). Fura‐2 loaded hippocampal slices were pcrfused continuously with 37°C oxygenated A‐CSF at 2ml/min flow rate. Slices were alternately excited with 340 and 380 nm light. The ratio or 2 signals was used to determine the change in intracellular free Ca 2+ . The effects of 3 mM VPA (estimated eflective concentration in the brain tissue: 693 pM) on 50 and 100 mM K+‐cvoked hippocam pal 5‐HT relcasc were deterinincd by in vivo microdialysis with ECD‐HPLC system in freely moving rats. A concentric dialysis probe was implanted into the hippocampus. The perfusion rate was always llp, 1/min, using modified Ringer's solution (MRS). MRS containing 50 or 100 mM K+ was perrused for 20 minutes. Results : Fifty and I00 mM K+‐evoked stimulation produced the elevation of intracellular Ca 2+ levels. Prc‐superfusion with therapeutic (700/AM) and supratherapcutic (3.5 mM) levels of VPA inhibited both 50 and I00 mM K+ ‐evoked elcvation of hippocampal intraccllular Ca 2+ levels in a concentration‐dependent manner (p