N-methyl-d-aspartate receptors in human erythroid precursor cells and in circulating red blood cells contribute to the intracellular calcium regulation

Abstract

The presence of N-methyl-D-aspartate receptor (NMDAR) was previously shown in rat red blood cells (RBCs) and in a UT-7/Epo human myeloid cell line differentiating into erythroid lineage. Here we have characterized the subunit composition of the NMDAR and monitored its function during human erythropoiesis and in circulating RBCs. Expression of the NMDARs subunits was assessed in erythroid progenitors during ex vivo erythropoiesis and in circulating human RBCs using quantitative PCR and flow cytometry. Receptor activity was monitored using a radiolabeled antagonist binding assay, live imaging of Ca 2ϩ uptake, patch clamp, and monitoring of cell volume changes. The receptor tetramers in erythroid precursor cells are composed of the NR1, NR2A, 2C, 2D, NR3A, and 3B subunits of which the glycine-binding NR3A and 3B and glutamate-binding NR2C and 2D subunits prevailed. Functional receptor is required for survival of erythroid precursors. Circulating RBCs retain a low number of the receptor copies that is higher in young cells compared with mature and senescent RBC populations. In circulating RBCs the receptor activity is controlled by plasma glutamate and glycine. Modulation of the NMDAR activity in RBCs by agonists or antagonists is associated with the alterations in whole cell ion currents. Activation of the receptor results in the transient Ca 2ϩ accumulation, cell shrinkage, and alteration in the intracellular pH, which is associated with the change in hemoglobin oxygen affinity. Thus functional NMDARs are present in erythroid precursor cells and in circulating RBCs. These receptors contribute to intracellular Ca 2ϩ homeostasis and modulate oxygen delivery to peripheral tissues.

Therapeutic Potential ofα7 Nicotinic Acetylcholine Receptors

“…However, expression of mRNAs in different tissues surprisingly revealed that genes encoding for ligand-gated ion channels are not exclusively expressed in neurons but can also be expressed in many other cell types. As an example, NMDA receptors are also expressed in red blood cells (Makhro et al, 2013). However, when considering biologic questions from a broader perspective, it became obvious that cells from different tissues might exploit the vast repertoire of membrane proteins encoded in the genome.…”

Functional plasticity of the N-methyl-d-aspartate receptor in differentiating human erythroid precursor cells

“…This strongly indicates the presence of multiple Ca 2+ uptake pathways in EPCs during differentiation (52). We have recently reported the presence of N -methyl- d -aspartate receptors (NMDARs) in human progenitor cells and have shown that these nonselective, ligand-gated cation channels mediate Ca 2+ uptake in EPCs (18, 35). …”

“…Indeed, these receptors have been reported in a variety of cells and tissues, including osteoclasts, megakaryocytes, leucocytes, and RBCs (28, 35, 37, 39, 41). NMDARs are formed of glycine-binding subunits GluN1 and GluN3A/3B, and glutamate-binding subunits GluN2A/2B/2C/2D (12, 46, 59).…”

Cardiac N-methyl d-aspartate Receptors as a Pharmacological Target

“…We have shown that subunit composition of cardiac NMDARs differs substantially from that in the brain (50) and resembles that in erythroid precursors and red cells (51). Mapping of the NMDAR subunits expression pattern within the heart chambers revealed that cardiac receptors formed by the GluN3A-GluN2D/2B with lower abundance of GluN1, 2A and 2C that are present at low levels in certain areas of the heart only ( Table 3).…”