Comparison of the effects of thapsigargin, 2,5-di-(tertbutyl)- 1,4-hydroquinone and cyclopiazonic acid on calcium release from rat liver endoplasmic reticulum
Abstract
The effects of three novel intracellular Ca2+-ATPase inhibitors on Ca2+ efflux from rat liver endoplasmic
reticulum (ER) were compared. The three inhibitors: thapsigargin (TG); 2,5-di-(tert-butyl)-1,4-hydroquinone (DBHQ) and
cyclopiazonic acid (CPA) released Ca2+ to various extents from the ER. Thapsigargin caused a slow but extensive release of
Ca2+ from the ER, releasing almost all the Ca2+ accumulated by the vesicles during the uptake phase. The other two
inhibitors did not release all the Ca2+ accumulated during the uptake phase. Furthermore, cyclopiazonic acid did not prevent
the re-uptake of the Ca2+ added after the release process. These findings suggest that there may be some intracellular Ca2+
stores which are insensitive to DBHQ and cyclopiazonic acid
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