Mutations in the presenilin-1 (PS-1) gene on chromosome 14 are linked to autosomal dominant early-onset Alzheimer's disease. The amino acid sequence of PS-1 predicts an integral membrane protein and immunocytochemical studies indicate that PS-1 is localized to endoplasmic reticulum (ER). We report that expression of PS-1 mutation L286V in cultured PC12 cells exaggerates Ca2+ responses to agonists (carbachol and bradykinin) that induce Ca2+ release from ER. Cells expressing L286V exhibit enhanced elevations of [Ca2+]i following exposure to amyloid beta-peptide (A beta) and increased vulnerability to A beta toxicity. An antagonist of voltage-dependent calcium channels (nifedipine), and a blocker of Ca2+ release from ER (dantrolene), counteract the adverse consequences of the PS-1 mutation. By perturbing Ca2+ homeostasis, PS-1 mutations may sensitize neurons to A beta-induced apoptosis.