Reversal in concentrations of actived CaMKII and calcineurin for long lasting stimulation

Abstract

The release of [3H]acetylcholine evoked by α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and its inhibition mediated by GABAA and glycine receptors were studied in superfused cultured rat embryo spinal cord motoneurons prelabeled with [3H]choline. AMPA elicited tritium release, possibly representing [3H]acetylcholine release in a concentration-dependent manner. The release was external Ca2+-dependent and was sensitive to Cd2+ ions, ω-conotoxin GVIA and ω-conotoxin MVIIC, but not to nifedipine, suggesting the involvement of N-, P/Q-, but not L-type Ca2+ channels. The AMPA effect was insensitive to tetrodotoxin. The glutamate receptors involved are AMPA type since the AMPA-evoked [3H]acetylcholine release was blocked by LY303070 and was potentiated by the antidesensitizing agent cyclothiazide. Muscimol inhibited completely the AMPA effect on [3H]acetylcholine release; muscimol was potentiated by diazepam and antagonized by SR95531, indicating the involvement of benzodiazepine-sensitive GABAA receptors. Glycine, acting at strychnine-sensitive receptors, also inhibited the effect of AMPA, but only in part. The inhibitory effects of muscimol and glycine are additive.We conclude that glutamate can act at AMPA receptors sited on spinal motoneurons to evoke release of acetylcholine. GABA and glycine, possibly released as cotransmitters from spinal interneurons, inhibit glutamate-evoked acetylcholine release by activating GABAA and glycine receptors on motoneurons.