CA200799 CellAura fluorescent H₁ antagonist [mepyramine]

The CellAura fluorescent H₁ antagonist [mepyramine] ligand was shown to antagonize the activity of the H₁ agonist, histamine, in the recombinant CHO cell line expressing the human H₁ receptor, co-transfected with a serum response element-induced secreted placental alkaline phosphatase (SPAP) reporter gene.

For the H₁ expressing cell line, the serum-induced expression of SPAP was measured under basal and 1% serum-stimulated (maximal) conditions.

Addition of CellAura fluorescent H₁ antagonist [mepyramine] to the basal or serum-stimulated cells did not significantly alter basal and stimulated SPAP levels, demonstrating that CellAura fluorescent H₁ antagonist [mepyramine] has no intrinsic agonist activity.

To determine the apparent K_D for CellAura fluorescent H₁ antagonist [mepyramine] at histamine H₁ receptors, cells were treated with varying concentrations of histamine agonist alone, or in the presence of 1µM CellAura fluorescent H₁ antagonist [mepyramine], and the serum-induced expression of SPAP measured. The apparent K_D at H₁ was calculated from the rightward shift of the agonist response curve in the presence of CellAura fluorescent H₁ antagonist [mepyramine], compared to the response curve for the agonist alone.

Similar studies were conducted with the CellAura fluorescent H₁ antagonist [mepyramine] ligand using recombinant CHO cell lines expressing either the human H₂ receptor or the human H₃ receptor and a cyclic AMP-responsive secreted placental alkaline phosphatase (SPAP) reporter gene. The apparent K_D at H₂ was calculated in the same way to that calculated for the human H₁ receptor.