NMDA Receptors as a Possible Component of Store-Operated Ca²⁺ Entry in Human T-Lymphocytes

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L. F. Zainullina, R. S. Yamidanov, V. A. Vakhitov, and Yu. V. Vakhitova^*

Institute of Biochemistry and Genetics, Ufa Research Center of the Russian Academy of Sciences, pr. Oktyabrya 71, 450054 Ufa, Russia; fax: (347) 235-6088; E-mail: juvv73@gmail.com

^* To whom correspondence should be addressed.

Received May 12, 2011; Revision received June 22, 2011

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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)P₃-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.

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KEY WORDS: human T-lymphocytes, NMDA receptors, T cell antigen receptor, store-operated Ca²⁺ entry, signaling cascades

DOI: 10.1134/S0006297911110034

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