reddit The amount of NE released by sympathetic nerve terminals will be most strongly influenced by a change in which of the following? Alpha receptor sensitivity Alpha receptor density Extracellular [Ca2+] COMT activity

Answer: Extracellular [Ca2+]

Explanation:

The sensitivity and density of the alpha receptors serve to enhance the response to the release of norepinephrine (NE). However, they do not exert a strong influence as the concentration of calcium ions on the amount of norepinephrine (NE) released by sympathic nerve terminals.

The release of neurotransmitters depends more on either an external or internal stimulus. This results in an action potential which on reaching a nerve terminal, results in the opening of Ca²⁺ channels in the neuronal membrane. Because the extracellular concentration of Ca²⁺ is greater than the intracellular Ca²⁺ concentration, Ca²⁺ flows into the nerve terminal. This triggers a series of events that cause the vesicles containing norepinephrine (NE) to fuse with the plasma membrane and release norepinephrine (NE) into the synapse. The higher the action potential, the higher the Ca²⁺ flow into the terminals resulting in higher amount of norepinephrine (NE) into the synapse, and vice versa.

Catechol-O-methyltransferase (COMT) is one of several enzymes that degrade catecholamines such as dopamine, epinephrine, and norepinephrine. It serves a regulatory purpose to lower the concentration of norepinephrine upon its release from nerve terminals.