The neurotransmitter acetylcholine is made in the cytosol...

The neurotransmitter acetylcholine is made in the cytosol and then transported into synaptic vesicles, where its concentration is more than 100 -fold higher than in the cytosol. When synaptic vesicles are isolated from neurons, they can take up additional acetylcholine added to the solution in which they are suspended, but only when ATP is present. Na $^{+}$ ions are not required for the uptake, but, curiously, raising the pH of the solution in which the synaptic vesicles are suspended increases the rate of uptake. Furthermore, transport is inhibited when drugs are added that make the membrane permeable to $\mathrm{H}^{+}$ ions. Suggest a mechanism that is consistent with all of these observations.

Key Concepts

Secondary Active Transport

Secondary active transport utilizes the energy stored in an ion gradient (in this case, the proton gradient) to move substances across the membrane without direct expenditure of ATP for the transported molecule. The neurotransmitter acetylcholine is taken up into synaptic vesicles through a transporter that exchanges protons for acetylcholine, thereby concentrating the neurotransmitter in the vesicle.

Proton Gradient (Electrochemical Gradient)

The proton gradient established by the ATP-driven pump consists of both a pH difference and an electrical potential across the vesicle membrane. This electrochemical gradient stores energy and is used to drive the uptake of neurotransmitters against their concentration gradients.

Active Transport

Active transport is a cellular process that moves substances against their concentration gradient using energy, usually derived from ATP. In neurons, this mechanism is essential for accumulating neurotransmitters like acetylcholine into synaptic vesicles, where their concentration far exceeds that in the cytosol.

ATP-Driven Proton Pump

ATP-driven proton pumps, such as vesicular H+-ATPases, use the energy from ATP hydrolysis to pump protons into synaptic vesicles. This activity creates a proton gradient (an acidic interior) that is critical for secondary transport mechanisms.

Transcript

00:01 Okay, we want to answer this question, we have to talk about acetylcholine and this experiment, okay? it says that neurotransmitter acetal chlorine is made up in the cytothol and then transported into cytopic.

00:12 So, for example, this is the axon of the neuron and this is a synaptic baron, okay, or an axon terminal.

00:20 And it is going to have here vesicles containing acetal coaling.

00:25 Okay, where here you have the skeletal muscle and here you have nickel.

00:30 In the ketene receptors.

00:32 Okay.

00:33 It says where its concentration is more than 100 full higher than in the cytos.

00:38 Okay, this is what we have up to now.

00:42 It means that the concentrations here inside the bicycles are 100 full higher than in the cytos.

00:47 What that means here.

00:49 When synatic vesicles are isolated from neurons, they can take up additional acetal calling added to the solution.

00:56 It means if we have here a solution, okay, and here we isolate it.

01:00 Basicles containing, let's make it bigger.

01:04 This is a basic called imaging and this is a container.

01:07 Here you have acetylcholine.

01:11 When senatite basicles are isolated from neurons, they can take up additional acetyl calling added to the solution.

01:16 So this is going to be the solution, and here we have a system make it like this.

01:21 Square.

01:22 The square is going to represent acetylcholine.

01:25 Okay.

01:26 They can take up additional acetylcholine added to the solution in which they are suspended, but only when 80p is present.

01:31 So this is going to use atp first...

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