Alpha subunit of calcium/calmodulin-dependent protein kinase enhances excitatory amino acid and synaptic responses of rat spinal dorsal horn neurons

Abstract

1. Here we report that in acutely isolated rat spinal dorsal horn (DH) neurons, the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA)/kainate and N-methyl-D-aspartate (NMDA) receptors can be regulated by endogenous and exogenous calcium/calmodulin-dependent protein kinase II (CaM-KII). Intracellularly applied, the alpha-subunit of CaM-KII enhanced AMPA/kainate and NMDA currents recorded with the use of the whole cell patch-clamp technique. 2. Microcystin, a nonselective phosphatases inhibitor, also enhances AMPA and NMDA responses. 3. Conventional intracellular recordings were made from substantia gelatinosa neurons in spinal cord slices to determine the effect of intracellular application of CaM-KII on excitatory synaptic potentials evoked by electrical stimulation of primary afferent fibers. Excitatory synaptic transmission was enhanced by CaM-KII, which is consistent with the importance of phosphorylation of the postsynaptic AMPA/kainate and NMDA receptor-ion complexes in the short- and long-term changes in synaptic transmission.

Calcium/calmodulin-dependent kinase II and long-term potentiation enhance synaptic transmission by the same mechanism.

“…The present results demonstrate that in hippocampal pyramidal cells in situ, CaM-K II enhances EPSCs and that this enhancement is due, at least in part, to an enhancement of AMPA receptor sensitivity, thus extending previous results in Al Extracellular cultured neurons (15) and spinal cord neurons (27). CaM-K II also caused an increase in the frequency of spontaneous EPSCs and a reduction in the number of failures of evoked responses.…”

“…(iv) One of the targets for CaM-K II is the AMPA receptor itself. Thus, activated CaM-K II can phosphorylate AMPA receptors in the postsynaptic density and can enhance responses to AMPA receptor agonists in cultured hippocampal neurons (15) and acutely isolated dorsal root ganglion neurons (27 evoked by activating GluRl receptors expressed in oocytes are also enhanced by CaM-K II (28).…”

Transition from Reversible to Persistent Binding of CaMKII to Postsynaptic Sites and NR2B

“…In contrast, NR2B can be phosphorylated directly by autonomous activity of bound CaMKII , which may serve to maintain the receptor in the phosphorylated state. Indeed, there is evidence that CaMKII activity can potentiate NMDAR currents (Kitamura et al, 1993;Kolaj et al, 1994). Several other CaMKII substrates are found in tight complexes with NMDARs (Yoshimura et al, 2000), and some may be directly phosphorylated by the autonomous activity of an NR2B-bound kinase subunit.…”

Nucleotides and Phosphorylation Bi-directionally Modulate Ca2+/Calmodulin-dependent Protein Kinase II (CaMKII) Binding to the N-Methyl-d-aspartate (NMDA) Receptor Subunit GluN2B

“…Binding to GluN2B keeps CaMKII in an active conformation, which allows phosphorylation of GluN2B even after the initial Ca 2ϩ stimulus has subsided, and even when T286 is no longer phosphorylated (15,17,31,32). In turn, CaMKII activity is thought to regulate NMDA-receptor currents (33)(34)(35). Remarkably, the major CaMKII phosphorylation site on GluN2B, S1303 (36), is located within the major CaMKII binding site on the receptor (15,27, for review see 4,5), and S1303 phosphorylation has been shown to interfere with CaMKII binding (27,37).…”