Cysteinyl leukotriene (CysLTs) induce intracellular calcium mobilization through the binding of two distinct seven-transmembrane, G protein-coupled receptors, designated CysLT1 Receptor and CysLT2 Receptor, to induce potent bronchoconstriction. Airway smooth muscle and macrophages express both receptor types, and additionally monocytes and eosinophils express CysLT1 Receptor, while cardiac Purkinje cells, adrenal medulla, peripheral blood leukocytes and brain also utilize CysLT2 Receptor. The effects of the CysLT Receptors can be blocked by antagonists, indicating a therapeutic mechanism for the treatment of asthma and allergies.