Altered intracellular Ca²⁺ signaling has been observed in cells derived from Alzheimer's disease patients, and a possible link between -secretase activity and the content of intracellular Ca²⁺ stores has been suggested. To test this hypothesis we studied the effects of a number of -secretase inhibitors on muscarinic receptor-mediated intracellular calcium release in the human salivary gland cell line HSG. Although several inhibitors in the peptide aldehyde class partially blocked carbachol-induced Ca²⁺ transients, these effects did not appear to be due to -secretase inhibition, and overall we found no evidence that inhibition of -secretase activity had any significant effect on agonist-induced intracellular calcium release in HSG cells. In complementary experiments with presenilin-null cells we found that the reconstitution of -secretase activity by transfection with wild-type presenilin 1 likewise had no significant effect on thapsigargin-induced Ca²⁺ release. In a test of the specific hypothesis that the level of AICD, intracellular fragment of the -amyloid precursor protein (APP) resulting from -secretase cleavage, can modulate the Ca²⁺ content of the endoplasmic reticulum, we were unable to demonstrate any effect of APP siRNA on the magnitude of carbachol-induced intracellular calcium release in HSG cells. Taken together our data cast considerable doubt on the hypothesis that there is a direct link between -secretase activity and the content of intracellular Ca²⁺ stores.