Receptor for cysteinyl leukotrienes mediating constriction of the microvascular smooth muscle during an inflammatory response. This response is mediated via a G-protein that activates a phosphatidylinositol-calcium second messenger system. The rank order of affinities for the leukotrienes is LTD4 >> LTE4 = LTC4 >> LTB4. Widely expressed, with higher expression in the lung and skin, intermediate levels in the heart, kidney and stomach and lower levels in several other tissues. Isoform 1 is the most abundant form in all tested tissues. MK-571, a selective antagonist, was shown to inhibit eosinophilia, bronchial hyperreactivity and microvascular leakage. Zafirlukast (Accolate) and pranlukast (Onon) were also shown to be selective antagonists. Belongs to the G-protein coupled receptor 1 family.