How does Serotonin effect Potassium.My professor told us that in the axon termin

Question

How does Serotonin effect Potassium.My professor told us that in the axon terminus serotonin will block Potassium from leaving because the inside of the terminus is -70 and if Potassium leaves that -70 would become even more negative and cause a decrease in the number of neurotransmitters released. But the membrane potential for Potassium is -94.2mV so I was thinking the -70 would become more positive if the Potassium left. Am I supposed to be looking at the cytosolic and interstitial numbers for potassium instead?

Explanation / Answer

If more potassium ions moves out of the cell,inspite of the fact that membrane potential inside the membrane is -70, then it will become more negative. It is not that if potassium ions have positive charge on them then the potential would also be positive. Negative values means, the relative abundance of one ion with respect to other ions across the both sides of the membrane. This would mean that if more potassium ions exits the cell, there will lesser amount of these ions inside, and so, more negative value of the membrane potential.

Serotonin is also a neuromodulator which is released into the synaptic cleft with the help of K+ ions as mediator. Serotonin first binds to Na+ present outside and then by the expense of energy of Na+/K+ pump, k+ ultimately helps in the serotonin release. Apart from this, release of any neurotransmitter reuqires the membrane to be depolarised (which is governed by Na+ and K+ ions only).

You are supposed to be looking at the inside of the cell because K+ is present in higher amounts towards inside and Na+ is present in higher amounts towards outside.

As it is stated in the question that potential for K+ is -94.2mV, so if the resting membrane potential is -70mv and further more K+ ions exits the cell then the potential will be more negative (not more positve) as there will be more deficiency of positive ions inside.

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