NMDA receptors as a possible component of store-operated Ca2+ entry in human T-lymphocytes

Abstract

Elevation of intracellular Ca²⁺ in T-lymphocytes as a consequence of T cell antigen receptor activation triggers transcriptional programs resulting in effector cytokine secretion and immune response coordination. Increase of Ca²⁺ concentration in T-lymphocytes follows both the Ins(1,4,5)P(3)-dependent release from an intracellular store and subsequent influx from extracellular milieu. Flow cytometry and the fluorescent dye Fluo-4AM have been used to demonstrate that noncompetitive NMDA receptor antagonist (+)-MK801 inhibits Ca²⁺ influx in T cells induced by thapsigargin. Combination of thapsigargin and (+)-MK801 with following incubation does not affect Ca²⁺ mobilization from intracellular stores, while decreased Ca²⁺ entry was observed. Overall data indicate that the ion channel blocker (+)-MK801 is able to inhibit the Ca²⁺ influx and confirm our suggestion about involvement of NMDA receptor in the store-operated Ca²⁺ entry mechanisms in human T-lymphocytes. To identify the signal transduction pathways associated with NMDA receptors in mitogen-stimulated T-lymphocytes, the cells were incubated with (+)-MK801, then activity of key phosphorylated protein kinases of MAP-activated (pERK1/2, pSAPK/JNK, p-p38), Ca²⁺-dependent (pCaMKII), PI3/Akt-dependent (pGSK-3β), and PKC-activated (pPKCθ) pathways were detected. The data we obtained demonstrate that (+)-MK801 treatment leads to more prominent decrease in Ras-activated protein kinases pERK1/2 and Rac-activated proteins p-p38 and pSAPK/JNK, as compared to DAG-dependent pPKCθ and Ca²⁺-dependent pCaMKII. These results show that NMDA receptors are mainly involved in regulation of Ras/Rac-dependent signaling in T-lymphocytes.

STIM Protein-NMDA2 Receptor Interaction Decreases NMDA-Dependent Calcium Levels in Cortical Neurons

“…Gonzalez-Sanchez et al measured SOCE and performed Ca 2+ store depletion in a medium containing physiological Ca 2+ concentrations [53], while we used the more common Ca 2+ re-addition protocol [45,54]. Yet, MK801 did inhibit SOCE in human T-lymphocytes under the conditions of Ca 2+ re-addition protocol [55]. Our results show that the increase in Ca 2+ after its addition can be mainly attributed to SOCE, but an additional small influx of Ca 2+ is also possible due to the activation of synapses.…”

Immunosuppression by N-Methyl-d-Aspartate Receptor Antagonists Is Mediated through Inhibition of Kv1.3 and KCa3.1 Channels in T Cells

“…Although CRAC channels can be activated at low membrane potential, the changed membrane potential will alter open probability and conductivity compared to the normal resting membrane potential. Therefore, the reduced Ca 2ϩ response in the presence of NMDAR antagonists is, at least partially, caused by lowering the Ca 2ϩ influx and by inhibition of the positive feedback function of Ca 2ϩ -induced activation of K Ca 3.1 channels during T-cell activation (56)(57)(58)(59)(60).…”

Weft, Warp, and Weave: The Intricate Tapestry of Calcium Channels Regulating T Lymphocyte Function

“…Interestingly, NMDA receptors have been shown to be expressed on rodent and human T cells and contribute to the increase in intracellular Ca 2+ level following T cell activation (Lombardi et al, 2001; Boldyrev et al, 2004; Miglio et al, 2005, 2007; Mashkina et al, 2007, 2010). Zainullina et al (2011) further demonstrated that activation of T cells with thapsigargin, an inhibitor of a Ca 2+ -ATPase of the ER that induces Ca 2+ store depletion and activation of plasma membrane Ca 2+ channels, in the presence of an NMDA receptor antagonist did not affect the movement of Ca 2+ from intracellular stores. However, it reduced the influx of Ca 2+ from the extracellular space suggesting that NMDA receptors participate in SOCE, at least to some degree.…”

“…However, it reduced the influx of Ca 2+ from the extracellular space suggesting that NMDA receptors participate in SOCE, at least to some degree. In this scenario, the NMDA receptors may be mainly contributing to Ras/Rac-dependent signaling in T cells following TCR engagement (Zainullina et al, 2011). Analogous to neuronal synapses, a recent study of thymocytes showed that upon TCR stimulation, NMDA receptors localize to the immunological synapse (Affaticati et al, 2011).…”