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PSYC 4750
Linda Hunter

The Basic Structure of Transmitter-Gated Channels  Four different types of polypeptides are used as subunits for the nicotinic receptor, and they are designated as: β, α, δ, and γ.  A complete mature channel is made from two α subunits, and one each of β, δ and γ.  There is one ACh binding site on each of the α subunits; the simultaneous binding of ACh to both sites is required for the channel to open  The structure of glutamate receptors resembles that of potassium channels, and this has inspired the surprising hypothesis that glutamate receptors and potassium channels evolved from a common ancestral ion channel Amino Acid-Gated Channels  Amino acid-gated channels mediate most of the fast synaptic transmission in the CNS  Several properties of these channels distinguish them from one another: o Pharmacology of their binding sites describes which transmitters affect them and how drugs interact with them o Kinetics of the transmitter binding process and channel gating determine the duration of their eff2+t o Selectivity of the ion channels determines whether they produce excitation or inhibition and whether Ca enters the cell in significant amounts o Conductance of open channels helps determine the magnitude of their effects Glutamate-Gated Channels:  3 Glutamate Receptor Subtypes: AMPA, NMDA, and Kainate  AMPA-gated and NMDA-gated channels mediate the bulk of fast excitatory synaptic transmission in the brain  AMPA-gated channels are permeable to both sodium and potassium but not calcium  AMPA channels can be activated by a rapid increase in sodium ions into the cell, thus depolarizing the cells  AMPA receptors coexist with NMDA receptors at many synapses in the brain, so most glutamate-mediated EPSPs have components contributed by both  NMDA-gated channels also cause excitation of a cell by admitting sodium, but they differ from AMPA receptors in two very important ways: o NMDA-gated channels are permeable to calcium o Inward ionic current through NMDA-gated channels is voltage dependent  If excessive amounts of calcium are released, it can trigger the death of a cell  Activation of NMDA receptors can cause widespread and lasting changes in the postsynaptic neuron  Inward ionic current through the NMDA channel is voltage dependent G-Protein-Coupled Receptors and Effectors  Transmission at the G-protein-coupled receptors involves 3 steps: o Binding of the neurotransmitter to the receptor protein o Activation of G-proteins o Activation of effector systems The Basic Structure of G-Protein-Coupled Receptors  Most G-protein-coupled receptors are simple variations on a common plan, consisting of a single polypeptide containing seven membrane-spanning alpha h
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