Presynaptic alpha-2 receptors on stimulation decrease the release of nor-epinephrine by certain mechanisms where as activation of beta presynaptic receptors increase or facilitates the nor epinephrine an effect which is opposite to the alpha receptors How does this facilitation of nor-epinephrine occur by the pre-synaptic beta receptors

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    $\begingroup$ This a very interesting question! I'm assuming the "presumptive" is a typo for presynaptic. I don't know what you mean by 'hetero tropic interaction' in this context (I thought that was for enzymes) but still, the alpha2 presynaptic acts by coupling with the Gi, thereby reducing Ca+2 and reducing vesicle release. How the beta presynaptic acts, I couldn't find out.. But increasing the calcium doesn't seem to be probable because beta receptrors couple with Gs and hence increase cAMP. Whether cAMP can induce vesicular fusion, that I don't know $\endgroup$ – Polisetty Nov 5 '16 at 6:33
  • $\begingroup$ @polisetty I looked heterotrpoic interaction to find that the alpha-2 receptors located presynaptically for the cholinergic neuron but postsynaptically to the sympathetic neuron inhibit the release of acetylcholine by binding to the gi specifically in the intestine where there is close proximity of the sympathetic and cholinergic neurons. Though the term hetertropic interaction might just be an interaction and not a mechanism for inhibition of neurotransmitter release. $\endgroup$ – Annette Black Nov 12 '16 at 11:19

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