Modulation of suicidal erythrocyte cation channels by an AMPA antagonist

In neurons alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are heteromeric cation channels composed of different sub-units, including GluA1-GluA4. When expressed without GluA2, AMPA receptors function as Ca(2+)-permeable cation channels. In erythrocytes, activation of Ca(2+)-permeable cation channels triggers suicidal erythrocyte death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with subsequent exposure of phosphatidylserine at the cell surface. Activators of the channels and thus eryptosis include removal of extracellular Cl(-) (replaced by gluconate) and energy depletion (removal of glucose). The present study explored whether GluA1 is expressed in human erythrocytes and whether pharmacological AMPA receptor inhibition modifies Ca(2+) entry and suicidal death of human erythrocytes. GluA1 protein abundance was determined by confocal microscopy, phosphatidylserine exposure was estimated from annexin V binding, cell volume from forward scatter in FACS analysis, cytosolic Ca(2+) concentration from Fluo3 fluorescence and channel activity by whole-cell patch-clamp recordings. As a result, GluA1 is indeed expressed in the erythrocyte cell membrane. The AMPA receptor antagonist NBQX (1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide) inhibited the cation channels following Cl(-) removal and the eryptosis following Cl(-) removal or energy depletion. The present study reveals a novel action of AMPA receptor antagonists and raises the possibility that GluA1 or a pharmacologically related protein participates in the regulation of Ca(2+) entry into and suicidal death of human erythrocytes.