Ca²⁺ release because of stimulation of different histamine receptors in EA.hy926 endothelial cells. Cells were treated with the following histamine receptor agonists at 100μM: trifluoromethyl-phenyl-histamine (H1-selective), amthamine dihydrobromide (H2-selective), immethridine dihydrobromide (H3-selective), clobenpropit dihydrobromide (H4-selective), and histamine in the presence of mepyramine, a selective H1 antagonist. (A) Bars show the increase in [Ca²⁺]_i after stimulation with each agonist. Error bars represent SEM; n = 3 independent experiments. (B) Representative calcium traces of experiment shown in panel A.