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Chapter 32: Problem 8

GTP \(\gamma\) S is a nonhydrolyzable analog of GTP. Experiments with squid giant axon synapses reveal that injection of GTyS into the presynaptic end (terminal) of the neuron inhibits neurotransmitter release (slowly and irreversibly). The calcium signals produced by presynaptic action potentials and the number of synaptic vesicles docking on the presynaptic membrane are unchanged by GTP \(\gamma\) S. Propose a model for neurotransmitter release that accounts for all of these observations.

Short Answer

Expert verified
GTP \(\gamma\) S likely inhibits a later step in the neurotransmitter release process such as the fusion of the vesicle with the presynaptic membrane, which is vital for releasing neurotransmitters into the synapse. This can explain why neurotransmitter release is inhibited without affecting calcium signals or vesicle docking.

Step by step solution

01

Understanding the role of calcium and vesicles

Firstly, understand that calcium signals are typically involved in initiating neurotransmitter release, triggering the synaptic vesicles to dock and release their neurotransmitters. The fact that these are unchanged means that GTP \(\gamma\) S is not interfering with the initial triggering of neurotransmitter release or vesicle docking.
02

Identifying the inhibition of GTP \(\gamma\) S

GTP \(\gamma\) S is inhibiting neurotransmitter release, but not affecting calcium signals or docking. This means that the inhibition must be occurring further downstream in the process.
03

Formulating a model

Therefore, we can formulate a model in which GTP \(\gamma\) S is making it impossible for vesicles to merge with the presynaptic membrane - a step that is necessary for the neurotransmitters to be released into the synapse. This might be done by blocking a necessary protein, or directly interfering with vesicle membrane fusion. The exact mechanism would depend on the specific biology of the system.

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