Regulated internalization of NMDA receptors drives PKD1-mediated suppression of the activity of residual cell-surface NMDA receptors.

Background: Constitutive and regulated internalization of cell surface proteins has been extensively investigated. The regulated internalization has been characterized as a principal mechanism for removing cell-surface receptors from the plasma membrane, and signaling to downstream targets of receptors. However, so far it is still not known whether the functional properties of remaining (non-internalized) receptor/channels may be regulated by internalization of the same class of receptor/channels.

Locally released small (non-protein) ninhydrin-reacting molecules underlie developmental differences of cultured medullary versus spinal dorsal horn neurons.

Neurons located in the trigeminal subnucleus caudalis (Vc) play crucial roles in pain and sensorimotor functions in the orofacial region. Because of many anatomical and functional similarities with the spinal dorsal horn (SDH), Vc has been termed the medullary dorsal horn--analogous to the SDH. Here, we report that when compared with embryonic SDH neurons in culture, neurons isolated from the Vc region showed significantly slower growth, lower glutamate receptor activity, and more cells undergoing cell death.

Regulation of voltage-gated sodium current by endogenous Src family kinases in cochlear spiral ganglion neurons in culture.

Voltage-gated sodium (Na+) and potassium (K+)channels have been found to be regulated by Src family kinases(SFKs).However, how these channels are regulated by SFKs in cochlear spiral ganglion neurons (SGNs) remains unknown.Here, we report that altering the activity of endogenous SFKs modulated voltage-gated Na+, but not K+, currents recorded in embryonic SGNs in culture.

The regulation of N-methyl-D-aspartate receptors by Src kinase.

Src family kinases (SFKs) play critical roles in the regulation of many cellular functions by growth factors, G-protein-coupled receptors and ligand-gated ion channels. Recent data have shown that SFKs serve as a convergent point of multiple signaling pathways regulating N-methyl-d-aspartate (NMDA) receptors in the central nervous system. Multiple SFK molecules, such as Src and Fyn, closely associate with their substrate, NMDA receptors, via indirect and direct binding mechanisms.

THE ROLE OF INTRACELLULAR SODIUM (Na) IN THE REGULATION OF CALCIUM (Ca)-MEDIATED SIGNALING AND TOXICITY.

It is known that activated N-methyl-D-aspartate receptors (NMDARs) are a major route of excessive calcium ion (Ca(2+)) entry in central neurons, which may activate degradative processes and thereby cause cell death. Therefore, NMDARs are now recognized to play a key role in the development of many diseases associated with injuries to the central nervous system (CNS). However, it remains a mystery how NMDAR activity is recruited in the cellular processes leading to excitotoxicity and how NMDAR activity can be controlled at a physiological level.

The NMDA receptor NR1 subunit is critically involved in the regulation of NMDA receptor activity by C-terminal Src kinase (Csk).

Previous studies have shown that Csk plays critical roles in the regulation of neural development, differentiation and glutamate-mediated synaptic plasticity. It has been found that Csk associates with the NR2A and 2B subunits of N-methyl-D-aspartate receptors (NMDARs) in a Src activity-dependent manner and serves as an intrinsic mechanism to provide a "brake" on the induction of long-term synaptic potentiation (LTP) mediated by NMDARs. In contrast to the NR2A and 2B subunits, no apparent tyrosine phosphorylation is found in the NR1 subunit of NMDARs.

Characterization of neuronal Src kinase purified from a bacterial expression system.

Neuronal Src (n-Src) is an alternative isoform of Src kinase containing a 6-amino acid insert in the SH3 domain that is highly expressed in neurons of the central nervous system (CNS). To investigate the function of n-Src, wild-type n-Src, constitutively active n-Src in which the C-tail tyrosine 535 was mutated to phenylalanine (n-Src/Y535F) and inactive n-Src in which the lysine 303 was mutated to arginine in addition to the mutation of Y535F (n-Src/K303R/Y535F), were expressed and purified from Escherichia coli BL21(DE3) cells. We found that all three types of n-Src constructs expressed at very high yields (∼500 mg/L) at 37°C, but formed inclusion bodies.