MW: 650.8. Thapsigargin is a cell-permeable inhibitor of the sarco-endoplasmatic reticulum Ca2+-ATPase (SERCA). This inhibition causes the release of intracellular Ca2+ stores. Thapsigargin also inhibits autophagy. This is due to the induction of and an ER stress response, which causes downstream effects that include an accumulation of autophagosomes in the cytosol. These intermediate structures never mature into amphisomes and autolysosomes, and the autophagy process cannot be completed.