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Persistent sodium current

Persistent sodium current is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Persistent sodium current rather than just read about it. In short: The persistent sodium current (INaP) (also called the "late sodium current" or "non/slow-inactivating sodium current") is a form of sub-threshold, biological electric current contributed by non-inactivating voltage-gated sodium channels found in several central neurons. INaP has been implicated in neuronal excitability, epilepsy, and neuropathic pain.

Persistent sodium current — main illustration
Persistent sodium current — illustration

Key takeaways

  • Persistent sodium current belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Persistent sodium current to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Persistent sodium current from memory before moving on to harder problems.

Reference excerpt

The persistent sodium current (INaP) (also called the "late sodium current" or "non/slow-inactivating sodium current") is a form of sub-threshold, biological electric current contributed by non-inactivating voltage-gated sodium channels found in several central neurons. INaP has been implicated in neuronal excitability, epilepsy, and neuropathic pain.

Biophysics Persistent sodium current generation is hypothesized to occur by the incomplete inactivation of the voltage-gated sodium channel current (INa), where the channel becomes constitutively active and conducts sodium, creating a "persistently active" inward sodium current. Upon depolarization, the four identical motifs of the sodium channel (which contain six transmembrane segments that include a pore-forming loop and a voltage sensor) move outward to allow for sodium influx. Sodium channels have the intrinsic ability to close rapidly following depolarization, and this current, named the "transient sodium current" is large and contributes to the bulk of the action potential. However, electrophysiological recordings which isolate INa find small amounts of current following depolarization which slowly inactivates, therefore contributing to the "persistent" or "non-inactivating" sodium current. The persistent sodium current also functions at sub-threshold voltages and is not only measured on depolarization of the membrane, and therefore may modulate neuronal excitability during the interspike interval of action potentials.

Health and disease INaP is involved in long QT syndrome, Brugada syndrome, and other inherited arrhythmias. Further, previous research has shown that increases in INaP contributes to hypoxia (medicine), demyelination, paroxysmal extreme pain disorder, and epilepsies. Pharmacological blockers of INaP are used clinically in many of these disorders. Amiodarone, while primarily blocking the human Ether-a-go-go-Related Gene potassium channel, has shown to significantly reduce persistent sodium current by 50% in cortical neurons as well as in cardiac sodium channel NaV1.5 and is used to treat arrhythmia. Cannabidiol has been used as an anti-epileptic for individuals with Dravet syndrome and may block the fast transient and persistent sodium currents, although in high concentration. GS967, also known as Prax330, is used to treat cardiac arrhythmias and surprisingly blocks the persistent sodium current in a study of Dravet syndrome which resulted in reduced seizures.

References

Illustrations

Persistent sodium current: This is a voltage-clamp recording of a voltage-gated sodium current from an acutely isolated mouse cerebellar Purkinje neuron.The "persistent sodium current" is defined in this instance as the remaining sodium current following the transient current. In this particular recording, the red trace shows a Purkinje neuron that was stepped from -90mV to 0mV for 5ms to inactivate all transient current, then repolarized at -45mV for 30ms. Here, the persistent sodium current is best measured at the end of the step. Typically, experimenters will use TTX-subtracted voltage-ramp protocols to measure the persistent sodium current
This is a voltage-clamp recording of a voltage-gated sodium current from an acutely isolated mouse cerebellar Purkinje neuron.The "persistent sodium current" is defined in this instance as the remaining sodium current following the transient current. In this particular recording, the red trace shows a Purkinje neuron that was stepped from -90mV to 0mV for 5ms to inactivate all transient current, then repolarized at -45mV for 30ms. Here, the persistent sodium current is best measured at the end of the step. Typically, experimenters will use TTX-subtracted voltage-ramp protocols to measure the persistent sodium current

Worked examples

Example 1 — a first encounter with Persistent sodium current

Start with the simplest possible case. Write down what Persistent sodium current claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Persistent sodium current before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Persistent sodium current ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Persistent sodium current

In research
Persistent sodium current appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Persistent sodium current in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Persistent sodium current is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrophysiology, so understanding it makes those chapters shorter.
In everyday life
Look for Persistent sodium current outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Persistent sodium current in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Persistent sodium current means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Persistent sodium current out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Persistent sodium current in simple terms?

The persistent sodium current (INaP) (also called the "late sodium current" or "non/slow-inactivating sodium current") is a form of sub-threshold, biological electric current contributed by non-inactivating voltage-gated sodium channels found in several central neurons. INaP has been implicated in…

Why does Persistent sodium current matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Persistent sodium current?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Persistent sodium current.

Tags

  • Electrophysiology

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