lecture 7 - Two alpha subunits beta gamma and lambda Each...

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9/27/07 Bio 317 Neurotransmitter release Calcium initiates vesicle fusion however magnesium acts as a calcium antagonist and binds to the same site as calcium with no efficacy. Low external calcium means low vesicle release. 10,000 per vesicle (called a quantum)…each quantal release is responsible for a 1 mV depolarization or polarization. Botulism toxin works on Snare complex Postsynaptic events Neurotransmitter diffuse across synapse Binds to ligand gate ion channel changes ion permeability and equilibrium membrane potential The Ach channel opens when binded to acetylcholine. The channel is both permeable to Sodium and Potassium however there is a net influx of sodium. Increasing permeability by X units to both sodium and potassium creates a much larger increase in sodium when in relativity to potassium permeability. Nictoinic Ach receptor
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Unformatted text preview: Two alpha subunits, beta, gamma, and lambda Each subunit has 4 transmembrane alpha helices (M1-M4) and each is coded by a different gene. Negative side chains on M2 allows for cation specificity The binding sites for acetylcholine is on the alpha subunits, therefore there are two binding sites per receptor. Upon the binding of the receptor it undergoes a conformational change and opens. However if open too long it inactivates Inactivation does not occur often in this channel because Acetylcholinesterase breaks down Ach really quickly and there is usually no chance for inactivation. However if the breaking down is inhibited in some way inactivation can occur. Excitatory transmission opens cation channel, inversely inhibitory transmission opens anion channel (or potassium channel)....
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