A novel tumour promoter, thapsigargin, transiently increases cytoplasmic free Ca2+ without generation of inositol phosphates in NG115-401L neuronal cells.
Thapsigargin, a sesquiterpene lactone with potent irritant and tumour-promoting activities, stimulates a rapid (within 15 s) transient increase in intracellular [Ca2+] in the NG115-401L neural cell line, as measured by the fluorescent indicator dye fura-2. This increase in cytoplasmic free [Ca2+] is concentration-dependent (ED50 around 20 nM) and occurs in the absence of extracellular Ca2+. Activation of NG115-401L cells by the inflammatory peptide bradykinin generates inositol phosphates, which parallel increases in intracellular [Ca2+]. However, the rise in cytoplasmic [Ca2+] stimulated by thapsigargin occurs in the absence of detectable production of inositol phosphates. Thapsigargin is unlike phorboid tumour promoters in that it has no action on two non-invasive indicators of phorbol stimulation of these cells, i.e. [3H]choline metabolite production and rise in intracellular pH. These data suggest that thapsigargin releases Ca2+ from an intracellular store by a novel mechanism, independent of the hydrolysis of phosphoinositides and concomitant activation of protein kinase C. Thus thapsigargin may provide a valuable tool for the analysis of intracellular signalling mechanisms.
D001920:Bradykinin / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002794:Choline / Q000378:metabolism; D004072:Digitonin / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism*; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010936:Plant Extracts / Q000494:pharmacology*; D010946:Plants, Medicinal / Q000032:analysis*; D013050:Spectrometry, Fluorescence; D013403:Sugar Phosphates / Q000378:metabolism*; D019284:Thapsigargin
D007295:Inositol Phosphates; D010936:Plant Extracts; D013403:Sugar Phosphates; D000001:Calcimycin; D019284:Thapsigargin; D004072:Digitonin; D002794:Choline; D001920:Bradykinin; D002118:Calcium