Thapsigargin is a cell-permeable sesquiterpene lactone found in the roots of Thapsia garganica. It is a tumor promoter and induces the release of intracellular stored Ca2+ without hydrolysis of inositolphospholipids via inhibition of the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA; IC50=30 nM). It may be used to distinguish between discrete intracellular Ca2+ pools. Thapsigargin-induced tumor promotion and down regulation of the EGF receptor is independent of protein kinase C activation.An inducer of stored Ca2+ release. Thapsigargin is a cell-permeable sesquiterpene lactone found in the roots of Thapsia garganica. It is a tumor promoter and induces the release of intracellular stored Ca2+ without hydrolysis of inositolphospholipids via inhibition of the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA; IC50=30 nM). It may be used to distinguish between discrete intracellular Ca2+ pools. Thapsigargin-induced tumor promotion and down regulation of the EGF receptor is independent of protein kinase C activation. An inducer of stored Ca2+ release.