Block of native Ca(2+)‐permeable AMPA receptors in rat brain by intracellular polyamines generates double rectification.

Abstract

1. The influence of intracellular factors on current rectification of different subtypes of native a-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs) was studied in rat brain slices by combining fast application of glutamate with patch pipette perfusion. 2. The peak current-voltage (I-V) relation of the AMPARs expressed in Bergmann glial cells of cerebellum and dentate gyrus (DG) basket cells of hippocampus was weakly rectifying in outside-out patches and nystatin-perforated vesicles, but showed a doubly rectifying shape with a region of reduced slope between 0 and +40 mV in nucleated patches. The I-V relation of AMPARs expressed in hippocampal CA3 pyramidal neurones was linear in all recording configurations. 3. Intracellular application of 25 /SM spermine, a naturally occurring polyamine, blocked outward currents in outside-out patches from Bergmann glial cells and DG basket cells in a voltage-dependent manner, generating I-V relations with a doubly rectifying shape which were similar to those recorded in nucleated patches. AMPARs in CA3 pyramidal cell patches were unaffected by 25 ,/M spermine.4. The half-maximal blocking concentration of spermine at +40 mV was 0'3 /M in Bergmann glial cell patches and 1S5,UM in DG basket cell patches, whereas it was much higher (> 100 sM) for CA3 pyramidal cell patches. Spermidine also affected current rectification, but with lower affinity. The block of outward current by polyamines following voltage jumps developed within < 0'5 ms. 5. We conclude that current rectification, rather than being an intrinsic property of the Ca2+-permeable AMPAR channel, is generated by polyamine block. a-Amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors (AMPARs) expressed in different types of neurones of the mammalian central nervous system (CNS) are molecularly diverse. Molecular cloning identified four AMPAR subunits, designated as GluR-A, -B, -C, and -D (or GluR1, 2, 3, and 4), from which the native receptors presumably are assembled. Studies on recombinant AMPARs expressed in Xenopus oocytes and human embryonic kidney (HEK 293) cells indicate that the subunit composition controls both Ca2+ permeability and current rectification. Recombinant AMPARs containing the edited GluR-B subunit show low Ca2+ permeability and linear or outwardly rectifying current-voltage (I-V) relations, whereas AMPARs lacking GluR-B exhibit high Ca2+ permeability and doubly or inwardly rectifying I-V relations (Hollmann, Hartley & Heinemann, 1991;Burnashev, Monyer, Seeburg & Sakmann, 1992b). Both functional properties are determined by the amino acid residue at the Q/R site of the pore-forming region which is either an arginine in the edited GluR-B subunit or a glutamine in the other subunits (Hollmann et at. 1991; Burnashev et al. 1992 b).For native AMPARs, the relation between CaP' permeability and current rectification is less clear than for recombinant AMPARs. In principal neurones of hippocampus and neocortex, AMPARs exhibit low Ca2+ permeability and linear or outwardly rectifying I-V ...

Subunit Composition, Kinetic, and Permeation Properties of AMPA Receptors in Single Neocortical Nonpyramidal Cells

“…Patch pipettes were pulled from borosilicate glass tubing and had a resistance of 5-10 M⍀ when filled with an internal solution containing (in mM): 144 K-gluconate, 3 MgC l 2 , 0.2 EGTA, 10 H EPES, 2 ATP, 0.2 GTP, and 100 M spermine, pH 7.2-7.4, 300 mOsm. Spermine was included because it maintains the voltage dependence of AM PARs in excised patches (Bowie et al, 1995;Kamboj et al, 1995;Koh et al, 1995). All potentials were corrected for junction potential (Ϫ12 mV) (Neher, 1992).…”

Chapter 13 Differential mechanisms of transmission and plasticity at mossy fiber synapses

“…Within the pore of AMPA receptors a single amino acid, the so-called Q/R site not only dictates their Ca permeability but also influences their sensitivity to block by both endogenous intracellular polyamines such as spermine and spermidine as well as externally applied polyamine toxins such as philanthotoxin (Bowie and Mayer, 1995;Kamboj et al, 1995;Koh et al, 1995; Isaac et al, in press). The interaction with intracellular polyamines is in part voltage-dependent, with block being greatest at depolarized potentials.…”

“…Traditionally most mechanisms of short-term synaptic plasticity are considered to be presynaptic in origin and typically arise from changes in the release probability due to accumulation of residual calcium loads, or exhaustion of the readily releasable pool of neurotransmitter. However, CP-AMPA receptors lacking the GluR2 subunit posses an unexpected and entirely postsynaptic form of short-term plasticity due to their susceptibility to block by intracellular polymines (Rozov et al, 1998;Rozov and Burnashev, 1999).Within the pore of AMPA receptors a single amino acid, the so-called Q/R site not only dictates their Ca permeability but also influences their sensitivity to block by both endogenous intracellular polyamines such as spermine and spermidine as well as externally applied polyamine toxins such as philanthotoxin (Bowie and Mayer, 1995;Kamboj et al, 1995;Koh et al, 1995; Isaac et al, in press). The interaction with intracellular polyamines is in part voltage-dependent, with block being greatest at depolarized potentials.…”

AMPA/Kainate Receptor-Mediated Downregulation of GABAergic Synaptic Transmission by Calcineurin after Seizures in the Developing Rat Brain

“…The most likely explanation for this was that Ca 2ϩ -permeable AMPARmediated activation of CaN resulted in CaN-mediated downmodulation of GABAergic inhibition. It is worth mentioning that in our voltage-clamp experiments, sIPSCs were recorded at the predicted AMPAR reversal potential (ϩ10 mV), and Ca 2ϩ -permeable AMPARs exhibit a voltage-dependent channel block by intracellular polyamines (Koh et al, 1995), resulting in smaller macroscopic currents. Thus, one might expect that Ca 2ϩ would be unable to enter recorded cells under this condition.…”