CN2011 Exam 2 Key - Exam questions 1. (AD) Evoked release...

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Exam questions 1. (AD) Evoked release of synaptic vesicles is a specialized form of the constitutive membrane trafficking pathway. Briefly describe a) the core fusion machinery shared by constitutive and evoked release including the names of the key proteins used for synaptic vesicle release and their localization, b) two key specializations of evoked synaptic vesicle release, c) the molecular mechanisms mediating the two specializations in (b), and (d) the utility of these specializations for efficient synaptic transmission. Sample answer a) The SNARE complex is essential for both constitutive and evoked release. For synaptic vesicle release, the SNARE complex includes synaptobrevin (VAMP), SNAP-25, and syntaxin. Synaptobrevin is a synaptic vesicle protein while SNAP-25 and syntaxin are on the presynaptic plasma membrane. b) 1) release occurs at active zones 2) release is calcium dependent c) 1) active zones—Munc-13 directs SNARE complex assembly to active zones by binding the active zone protein RIM. RIM binds calcium channels. This physically links releasable synaptic vesicles to sites of calcium entry. 2) calcium dependence—when calcium binds synaptotagmin then synaptotagmin binds lipids and the SNARE complex, promoting fusion. Complexin also promotes calcium- dependent release, in part by acting as a fusion clamp to inhibit spontaneous synaptic vesicle fusion. d) 1) limiting release to active zones ensures that transmitter is released directly opposite the postsynaptic density, so that postsynaptic transmitter receptors see a high concentration of transmitter 2) calcium-dependence of release allows action potentials to trigger release. This has many advantages including 1) allowing information about excitability in the presynaptic cell to be transmitted to the postsynaptic cell and 2) allowing for the synchronous release of transmitter from many release sites. 2. (SM) You record in current clamp from a postsynaptic neuron and stimulate a presynaptic input. The resting potential of the recorded cell is -80 mV. The postsynaptic potential depolarizes the target cell by 5 mV at peak and decays with a time constant of 30 ms. A. Propose the necessary experiments to determine whether the PSP is excitatory or inhibitory. B. You conclude that the channels underlying the PSP close with a deactivation time constant of 30 ms. Why is this conclusion flawed? Assuming you have any technique available to you discussed in lectures, what is a better experiment to determine the deactivation time of the synaptic conductance? A. You must know the reversal potential of the synaptic conductance relative to the voltage threshold for action potential initiation. Action potential threshold can be determined by direct depolarizing current injection and measuring the voltage of the action potential upswing. Second, voltage clamp the cell and measure the reversal potential of the PSC. If the reversal potential is positive to the voltage threshold for action potentials, the PSP is
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This note was uploaded on 02/27/2012 for the course BIO 5571 taught by Professor P.taghert during the Fall '11 term at Washington University in St. Louis.

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CN2011 Exam 2 Key - Exam questions 1. (AD) Evoked release...

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