You have prepared lipid micelles that possess a leaky Na+ion channel, and, for purposes of experimentation,...

You have prepared lipid micelles that possess a leaky Na+ion channel, and, for purposes of experimentation, the cytosolic sides of the channels are facing outward. Predict what will happen with the Na+ ion movement and the probable impact on thedevelopment of an action potential across the micelle membrane if(a) there were an equivalent amounts of Na+ ions on both sides of the membrane, (b)a greater Na+ ion concentration inside the micelle, and (c) a greater concentration of Na+ions outside the micelle. Explain you answer in each case.

Expert Solution

Answer:

Explanation: The answers for the question are explained in the column 3 and 4 of the below table. But in order to understand that, the behaviour in the normal lipid micells whose cytosolic sides are facing inwards are explained in column 2

Brief synopsis about Sodium ions and its concentration in action potential:

1. Extracellular fluids (ECF) contains high concentration of Sodium ions (along with Chloride ions)

2. During depolarization phase, Voltage gated Sodium channels open and causes influx of sodium ions into the cytosol

3. In the next step, there is outflux of sodium ions (as inactivatation gates of voltage gated sodium channel are closed), resulting in cell repolarization occurs.

4. Sodium channel is now closed and inactivation gate of sodium channel is open. Sodium ions pass through passive channels bringing back the resting membrane potential

In the given question leakage channels (also called as Passive channels) are altered. Passive channels are responsible for bringing back the resting membrane potential.

Condition	Normal lipid micelles (Cytosolic sides facing inwards)	Experimental micelles (cytosolic sides of channels facing outwards)	Explanation
a. Equivalent amounts of Na+ ions on both sides of the membrane	No change or no movement of sodium ions	No change or no movement of sodium ions	as the channel is a passive channel, the movement of ions is based on concentration gradient. Since there is no concentration gradient, there is no net movement
b. Greater Na+ ions inside the micelle	Movement of sodium ions from inside of the to the outside. Aided by Na+ K+ ATP ase pump which brings K+ to diffuse sodium outside	Movement of sodium ions from inside to the outside. Since there is only Na+ leak channels and no mention about the Na+ K+ ATPase pump, there is slow movement of sodium ions which delays to get the resting membrane potential	Usually the movement of sodium ions is solely based on concentration gradient in sodium leak channels.
c. Greater concentration of Na+ ions outside the micelle	In normal cells there are only few Sodium leak channels, hence, there is slow diffusion of sodium ions into the cytosol. This is countered by Na+K+ ATP ase pump which moves sodium out and potassium in	In the given case of altered cell there is continous influx of sodium ions into the cytosol owing to concentration gradient. This is not countered by Na+K+ ATP ase pump	Since sodium leak channels are passive and function by concentration gradient, the sodium ions move from outside to inside in the given lipid micelle

gladiator answered 2 years ago

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