Synaptic ligands

Synaptic Transmission. Figure 1 Synaptic transmission. The presynaptic terminal contains voltage-dependent Na Superscript and Ca2+ channels, vesicles with a vesicular neurotransmitter transporter VNT, a plasmalemmal neurotransmitter transporter PNT, and a presynaptic G protein-coupled receptor GPCR with its G protein and its effector E the inset also shows the vesicular H+ pump. The postsynaptic cell contains two ligand-gated ion channels LGIC, one for Na+ and K+ and one for Cl-, a postsynaptic GPRC, and a PNT. In this synapse, released transmitter is inactivated by uptake into cells. 

Of the several classes of receptors for endogenous chemical signals [3], two are used as postsynaptic receptors in synaptic transmission ligand-gated ion channels (LGICs) and G protein-coupled receptors (GPCRs Fig. 1). Due to the large number of transmitters and the existence of several receptor types for almost all, postsynaptic receptor activation is the most diversified step of synaptic transmission. Table 1 shows selected neurotransmitter receptors. 

In addition to the pre-synaptic effects, CX3CL1 modulates the functional properties of ligand-gated channels at post-synaptic sites. In SK-N-SH cells, a human neuroblastoma cell line, CX3CL1 reduces the amplitude of NMDA-induced calcium transients (Deiva et al. 2004). In these cells, CX3CL1 application causes a PTX insensitive transient increase in the intracellular Ca " concentration dependent on... 

Figure 2.5. The synapse. GPCR = guanine nucleotide-binding protein-coupled receptor, LGICR = ligand-gated ion channel receptor, SB = synaptic bouton, T = neurotransmitter, YOC = voltage-operated ion channel protein, YOCC = voltage-operated calcium channel protein, Ast = astrocyte, AA = axoaxonal synapse, ASD = axosomatic or axodendritic synapse. GPCR 1 = receptor protein, 2 = G-protein, 3 = enzyme, 4 = ion channel protein.

It has been observed that the IP3-R can be activated in the absence of its ligand, I(1,4,5)P3> by a group of proteins termed Ca2+-binding proteins (CaBPs), a subfamily of E-F hand-containing proteins known as neuronal Ca2+ sensors [17]. These proteins are exclusively expressed in neurons and are particularly enriched in synaptic/dendritic fields. 

Cyclic AMP can be viewed as subserving two major functions in the nervous system. First, cAMP mediates some short-term aspects of synaptic transmission some rapid actions of certain neurotransmitters on ion channels that do not involve ligand-gated channels are mediated through cAMP. 

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