Drosophila tachykinin receptor, a neurokinin receptor cloned from the fruit fly Drosophila melanogaster, is a G-protein-coupled receptor, which upon activation by a peptide agonist induces a transient increase in the concentration of intracellular calcium. The functional assay based on aequorin-derived luminescence triggered by receptor-mediated changes in Ca(2+) levels was used to examine and compare the effect of tachykinin-related peptides from different species. Among the endogenous Drosophila peptides, Drm-TK I induced the strongest calcium response. The most potent tachykinin-related peptides from Leucophaea maderae, Locusta migratoria, and Calliphora vomitoria, were partial agonists at the Drosophila tachykinin receptor