If a mutation of the gene coding for voltagegated sodium cha

If a mutation of the gene coding for voltage-gated sodium channel occurs, resulting in channels that do not have the globular part of the protein, usually referred to as the ball, these channels would not be able to inactivate. Which of the following would you expect to see in neurons expressing the mutated channel?

A. A change in the ion selectivity of the channel of the mutated channels, allowing ions other than sodium to move through it.

B. A prolonged action potential that takes longer than normal to return to resting membrane potential.

C. An outward flow of sodium ions during the initial part of the action potential.

D. A change in the voltage sensitivity of the channel so that it does not open until more depolarized voltages.

Solution

B. A prolonged action potential that takes longer than normal to return to resting membrane potential.

Before an action potential occurs, the axonal membrane is at its normal resting potential, and Na⁺ channels are in their deactivated state, blocked on the extracellular side by their activation gates. In response to an electric current (in this case, an action potential), the activation gates open, allowing positively charged Na⁺ ions to flow into the neuron through the channels, and causing the voltage across the neuronal membrane to increase.

At the peak of the action potential, when enough Na⁺ has entered the neuron and the membrane\'s potential has become high enough, the Na⁺ channels inactivate themselves by closing their inactivation gates. Closure of the inactivation gate causes Na⁺flow through the channel to stop, which in turn causes the membrane potential to stop rising. With its inactivation gate closed, the channel is said to be inactivated. With the Na⁺ channel no longer contributing to the membrane potential, the potential decreases back to its resting potential as the neuron repolarizes .

When these channels would not be able to inactivate, inactivation gates would not be closed and Na+ ions will continue to enter into the neuron which will prolong action potential