Muscarinic Receptor Stimulation of D‐aspartate Uptake Into Human SH‐SY5Y Neuroblastoma Cells Is Attenuated By Hyposmolarity

Abstract

In the present study, the ability of muscarinic cholinergic receptors (mAChRs) to regulate the uptake of glutamate (monitored as D‐aspartate) into human SH‐SY5Y neuroblastoma cells under isotonic or hypotonic conditions has been examined. In isotonic media, agonist activation of mAChRs resulted in a significant increase (250–300% of control) in the uptake of D‐aspartate and concurrently, a cellular redistribution of the excitatory amino acid transporter 3 (EAAT3) to the plasma membrane. In hypotonic media, the ability of mAChR activation to facilitate D‐aspartate uptake was significantly attenuated (40–50%) and the cellular distribution of EAAT3 was disrupted. Reduction of mAChR‐stimulated D‐aspartate uptake under hyposmotic conditions could be fully reversed upon re‐exposure of the cells to isotonic media. Under both isotonic and hypotonic conditions, mAChR‐mediated increases in D‐aspartate uptake were dependent upon cytoskeletal integrity, protein kinase C (PKC) and phosphatidylinositol 3‐kinase (PI3K) activities and the availability of intracellular Ca2+. In contrast, a dependence on extracellular Ca2+ was only observed under isotonic conditions. The results suggest that although the uptake of D‐aspartate into SH‐SY5Y cells is enhanced following mAChR activation, this process is markedly attenuated by hyposmolarity. Supported by GM007767 (DJF).