The Histamine 3 (Ha) Receptor is a G-protein linked receptor that, in its active
ID: 3165852 • Letter: T
Question
The Histamine 3 (Ha) Receptor is a G-protein linked receptor that, in its active conformation, interacts with a G-protein leading to (among other effects) closing Ca2 channels that otherwise let Ca*2 into a cell: i.e. Ha receptor activation leads to a decreass in lower) Ca2 influx. The Ha receptor is important in regulation of how much neurotransmitter neurons release into synapses and dysregulation of Hs receptor activity is implicated in a number of neurological disorders including narcolepsy, A Tourette's syndrome and schizophrenia. For each condition described below, indicate whether a cell (in a cell culture) that expresses the Ha receptor will have () higher, (i) lower or (iil equal Car2 influx as a comparable cell not exposed to any compound binding the Ha receptor. Assume that all the ligands bind in the same location on the protein surface, unless otherwise indicated (1 point each, binding constants from Parsons and Ganellin, 2006 or Wikipedia, accessed 11 April 2018) Addition (to a concentration of 10 HM) of histamine which binds the active state of the Hs receptor, with a Ks of 5 HM, but not to the inactive state (A) Addition (to a concentration of 0.5 nM) of Clobenpropit, which binds both the active and inactive states of the Ha receptor with a Ke of 0.6 nM (B) (C) Addition of histamine (to a concentration of 10 nM) and Clobenpropit (to a concentration of 1 nM). (D) Addition of histamine (to a concentration of 10 HM) and Clobenpropit (to a concentration of 0.5 nM) Addition of Pitolisant (to a concentration of 1 nM) which binds the inactive form of the H3 receptor with a Ke of 0.2 nM (E)Explanation / Answer
Please find the answers below:
Answer A: Since clobenpropit is an antagonist of histamine receptor, it will prevent influx of calcium ions even when it binds to the receptor in inactive state.
Answer B: Higher influx of calcium will be experienced since the active state of the receptor will promote further inward movement of calcium ions.
Answer C: Enhanced influx of calcium will be experienced since histamine and clobenpropite both will promote opening of the calcium channels in this case.
Answer D: A sudden blockage of calcium influx will be experienced due to active binding of clobenpropit to the histamine receptors in presence of histamine.
Answer E: Increase in total calcium influx will be experienced since pitolisant favors opening of these receptors.
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